ALBERT

Description: The age of secondary carbonate mineralization in the martian meteorite ALH84001 was determined to be 3.90 +/- 0.04 billion years by rubidium-strontium (Rb-Sr) dating and 4.04 +/- 0.10 billion years by lead-lead (Pb-Pb) dating. The Rb-Sr and Pb-Pb isochrons are defined by leachates of a mixture of high-graded carbonate (visually estimated as approximately 5 percent), whitlockite (trace), and orthopyroxene (approximately 95 percent). The carbonate formation age is contemporaneous with a period in martian history when the surface is thought to have had flowing water, but also was undergoing heavy bombardment by meteorites. Therefore, this age does not distinguish between aqueous and impact origins for the carbonates.

Description: Hydrogen peroxide chemisorbed on titanium dioxide (peroxide-modified titanium dioxide) is investigated as a chemical analog to the putative soil oxidants responsible for the chemical reactivity seen in the Viking biology experiments. When peroxide-modified titanium dioxide (anatase) was exposed to a solution similar to the Viking labeled release (LR) experiment organic medium, CO2 gas was released into the sample cell headspace. Storage of these samples at 10 degrees C for 48 hr prior to exposure to organics resulted in a positive response while storage for 7 days did not. In the Viking LR experiment, storage of the Martian surface samples for 2 sols (approximately 49 hr) resulted in a positive response while storage for 141 sols essentially eliminated the initial rapid release of CO2. Heating the peroxide-modified titanium dioxide to 50 degrees C prior to exposure to organics resulted in a negative response. This is similar to, but not identical to, the Viking samples where heating to approximately 46 degrees C diminished the response by 54-80% and heating to 51.5 apparently eliminated the response. When exposed to water vapor, the peroxide-modified titanium dioxide samples release O2 in a manner similar to the release seen in the Viking gas exchange experiment (GEx). Reactivity is retained upon heating at 50 degrees C for three hours, distinguishing this active agent from the one responsible for the release of CO2 from aqueous organics. The release of CO2 by the peroxide-modified titanium dioxide is attributed to the decomposition of organics by outer-sphere peroxide complexes associated with surface hydroxyl groups, while the release of O2 upon humidification is attributed to more stable inner-sphere peroxide complexes associated with Ti4+ cations. Heating the peroxide-modified titanium dioxide to 145 degrees C inhibited the release of O2, while in the Viking experiments heating to this temperature diminished but did not eliminated the response. Although the thermal stability of the titanium-peroxide complexes in this work is lower than the stability seen in the Viking experiments, it is expected that similar types of complexes will form in titanium containing minerals other than anatase and the stability of these complexes will vary with surface hydroxylation and mineralogy.

Description: Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant observed from the Galileo spacecraft show absorption features resulting from hydrogen peroxide. Comparisons with laboratory measurements indicate surface hydrogen peroxide concentrations of about 0.13 percent, by number, relative to water ice. The inferred abundance is consistent with radiolytic production of hydrogen peroxide by intense energetic particle bombardment and demonstrates that Europa's surface chemistry is dominated by radiolysis.

Description: No abstract available

Description: The Mayak Production Association was the first Russian site for the production and separation of plutonium. The extensive increase in plutonium production during 1948-1955, as well as the absence of reliable waste-management technology, resulted in significant releases of liquid radioactive effluent into the rather small Techa River. This resulted in chronic external and internal exposure of about 30,000 residents of riverside communities; these residents form the cohort of an epidemiologic investigation. Analysis of the available historical monitoring data indicates that the following reliable data sets can be used for reconstruction of doses received during the early periods of operation of the Mayak Production Association: Temporal pattern of specific beta activity of river water for several sites in the upper Techa region since July 1951; average annual values of specific beta activity of river water and bottom sediments as a function of downstream distance for the whole river since 1951; external gamma-exposure rates near the shoreline as a function of downstream distance for the whole Techa River since 1952; and external gamma-exposure rate as a function of distance from the shoreline for several sites in the upper and middle Techa since 1951.

Description: An option in the long-duration exploration of space, whether on the Moon or Mars or in a spacecraft on its way to Mars or the asteroids, is to utilize a bioregenerative life-support system in addition to the physicochemical systems that will always be necessary. Green plants can use the energy of light to remove carbon dioxide from the atmosphere and add oxygen to it while at the same time synthesizing food for the space travelers. The water that crop plants transpire can be condensed in pure form, contributing to the water purification system. An added bonus is that green plants provide a familiar environment for humans far from their home planet. The down side is that such a bioregenerative life-support system--called a controlled environment life-support system (CELSS) in this paper--must be highly complex and relatively massive to maintain a proper composition of the atmosphere while also providing food. Thus, launch costs will be high. Except for resupply and removal of nonrecycleable substances, such a system is nearly closed with respect to matter but open with respect to energy. Although a CELSS facility is small compared to the Earth's biosphere, it must be large enough to feed humans and provide a suitable atmosphere for them. A functioning CELSS can only be created with the help of today's advanced technology, especially computerized controls. Needed are energy for light, possibly from a nuclear power plant, and equipment to provide a suitable environment for plant growth, including a way to supply plants with the necessary mineral nutrients. All this constitutes the biomass production unit. There must also be food preparation facilities and a means to recycle or dispose of waste materials and there must be control equipment to keep the facility running. Humans are part of the system as well as plants and possibly animals. Human brain power will often be needed to keep the system functional in spite of the best computer-driven controls. The particulars of a CELSS facility depend strongly on where it is to be located. The presence of gravity on the Moon and Mars simplifies the design for a facility on those bodies, but a spacecraft in microgravity is a much more challenging environment. One problem is that plants, which are very sensitive to gravity, might not grow and produce food in the virtual absence of gravity. However, the experience with growing super-dwarf wheat in the Russian space station Mir, while not entirely successful because of the sterile wheat heads, was highly encouraging. The plants grew well for 123 days, producing more biomass than had been produced in space before. This was due to the high photon flux available to the plants and the careful control of substrate moisture. The sterile heads were probably due to the failure to remove the gaseous plant hormone, ethylene, from the Mir atmosphere. Since ethylene can easily be removed, it should be possible to grow wheat and other crops in microgravity with the production of viable seeds. On the ground Biosphere-2 taught us several lessons about the design and construction of a CELSS facility, but Bios-3 came much closer to achieving the goals of such a facility. Although stability was never completely reached, Bios-3 was much more stable than Biosphere-2 apparently because every effort was made to keep the system simple and to use the best technology available to maintain control. Wastes were not recycled in Bios-3 except for urine, and inedible plant materials were incinerated to restore CO2 to the atmosphere. Since much meat (about 20% of calories) was imported, closure in the Bios-3 experiments was well below 100%. But then, a practical CELSS on the Moon might also depend on regular resupply from Earth. Several important lessons have been learned from the CELSS research described in this review.

Description: A major argument in the claim that life had been discovered during the Viking mission to Mars is that the results obtained in the Labeled Release (LR) experiment are analogous to those observed with terrestrial microorganisms. This assertion is critically examined and found to be implausible.

Description: Determining the source of Earth's oceans is a longstanding problem in planetary science. Possible sources of water include water ice or water of hydration of silicate minerals in the original material from which the bulk Earth accreted and water brought in by late-arriving planetesimals during the heavy bombardment period (4.5-3.8 Gyr ago) [Chyba, 1989, 1991]. Comets are an attractive source of water because their origin in the outer solar system is consistent with the long timescale for heavy bombardment. However, the high deuterium/hydrogen (D/H) ratio of the three comets that have been studied, Halley, Hyakutake, and Hale-Bopp, indicates that Earth must have had a source with a low-D/H ratio as well. Here we suggest that solar wind-implanted hydrogen on interplanetary dust particles (IDPs) provided the necessary low-D/H component of Earth's water inventory.

Description: Chemical compositions of impact melt glass veins, called Lithology C (Lith C) in Martian meteorite EET79001 were determined by electron microprobe analysis. A large enrichment of S, and significant enrichments of Al, Ca, and Na were observed in Lith C glass compared to Lithology A (Lith A). The S enrichment is due to mixing of plagioclase- enriched Lith A material with Martian soil, either prior to or during impact on Mars. A mixture of 87% Lith A, 7% plagioclase, and 6% Martian soil reproduces the average elemental abundances observed in Lith C. Shock melting of such a mixture of plagioclase-enriched, fine-grained Lith A host rock and Martian soil could yield large excesses of S (observed in this study) and Martian atmospheric noble gases (found by Bogard et al., 1983) in Lith C. These mixing proportions can be used to constrain the elemental abundance of phosphorus in Martian soil.

Description: The Techa River (Southern Urals, Russia) was contaminated in 1949-1956 by liquid radioactive wastes from the Mayak complex, the first Russian facility for the production of plutonium. The measurements of environmental contamination were started in 1951. A simple model describing radionuclide transport along the free-flowing river and the accumulation of radionuclides by bottom sediments is presented. This model successfully correlates the rates of radionuclide releases as reconstructed by the Mayak experts, hydrological data, and available environmental monitoring data for the early period of contamination (1949-1951). The model was developed to reconstruct doses for people who lived in the riverside communities during the period of the releases and who were chronically exposed to external and internal irradiation. The model fills the data gaps and permits reconstruction of external gamma-exposure rates in air on the river bank and radionuclide concentrations in river water used for drinking and other household needs in 1949-1951.

Description: Crystals of halite and sylvite within the Monahans (1998) H5 chondrite contain aqueous fluid inclusions. The fluids are dominantly sodium chloride-potassium chloride brines, but they also contain divalent cations such as iron, magnesium, or calcium. Two possible origins for the brines are indigenous fluids flowing within the asteroid and exogenous fluids delivered into the asteroid surface from a salt-containing icy object.

Description: An off-limb scan of Callisto was conducted by the Galileo near-infrared mapping spectrometer to search for a carbon dioxide atmosphere. Airglow in the carbon dioxide nu3 band was observed up to 100 kilometers above the surface and indicates the presence of a tenuous carbon dioxide atmosphere with surface pressure of 7.5 x 10(-12) bar and a temperature of about 150 kelvin, close to the surface temperature. A lifetime on the order of 4 years is suggested, based on photoionization and magnetospheric sweeping. Either the atmosphere is transient and was formed recently or some process is currently supplying carbon dioxide to the atmosphere.

Description: In the 20 years since the Viking experiments, major advances have been made in the areas of microbial systematics, microbial metabolism, microbial survival capacity, and the definition of environments on earth, suggesting that life is more versatile and tenacious than was previously appreciated. Almost all niches on earth which have available energy, and which are compatible with the chemistry of carbon-carbon bonds, are known to be inhabited by bacteria. The oldest known bacteria on earth apparently evolved soon after the formation of the planet, and are heat loving, hydrogen and/or sulfur metabolizing forms. Among the two microbial domains (kingdoms) is a great deal of metabolic diversity, with members of these forms being able to grow on almost any known energy source, organic or inorganic, and to utilize an impressive array of electron acceptors for anaerobic respiration. Both hydrothermal environments and the deep subsurface environments have been shown to support large populations of bacteria, growing on energy supplied by geothermal energy, thus isolating these ecosystems from the rest of the global biogeochemical cycles. This knowledge, coupled with new insights into the history of the solar system, allow one to speculate on possible evolution and survival of life forms on Mars.

Description: Utilization of extraterrestrial resources, or In-Situ Resource Utilization (ISRU), is viewed as an enabling technology for the exploration and commercial exploitation of our solar system. It is fundamental to any program of extended human presence and operation on other extraterrestrial bodies that we learn how to utilize the indigenous resources. The chief benefits of ISRU are that it can reduce the mass, cost, and risk of robotic and human exploration while providing capabilities that the enable commercial development of space. A key subset of ISRU which has significant cost and risk reduction benefits for robotic and human exploration, and which requires a minimum of infrastructure, is In-Situ Consumable Production (ISCP). ISCP involves acquiring, manufacturing, and storing propellants for planetary ascent or Earth return vehicles, gases and water for crew and life support, and fuel cell reagents for power generation by using resources available at the site of exploration. Since propellant mass typically makes up 60 to 80% of the ascent or Earth return vehicle mass, In-Situ Propellant Production (ISPP) on the Lunar or Mars surface can significantly reduce the overall mass for the return vehicle needed to be brought from Earth. Systems analyses of human Mars missions have indicated that solely producing propellants on the surface of Mars by processing atmospheric carbon dioxide can reduce the initial mission mass required in low Earth orbit by approximately 20% as compared to carrying all required propellant to the Mars surface from Earth. An even greater leverage can occur for Mars missions when in-situ water can be processed.

Description: Mars 2001 presents an exciting opportunity for advances in radiation risk management of a future human mission to Mars. The mission timing is particularly fortuitous, coming just after solar maxinuun, when there will be a high probability to observe significant solar particle events (SPEs). A major objective of this mission is to characterize the Martian radiation environment to support future human missions to Mars. In addition, the MARIE instruments on the Lander and Orbiter, designed to measure the energetic particle flux at Mars, can be used during the cruise phase to provide multipoint observations of SPEs in the critical region of the heliosphere (1 to 1.5 AU) needed to reduce the in-flight radiation risk to a future Mars-bound crew.

Description: Protection against the hazards from exposure to ionizing radiation remains an unresolved issue in the Human Exploration and Development of Space (HEDS) enterprise [1]. The major uncertainty is the lack of data on biological response to galactic cosmic ray (GCR) exposures but even a full understanding of the physical interaction of GCR with shielding and body tissues is not yet available and has a potentially large impact on mission costs. "The general opinion is that the initial flights should be short-stay missions performed as fast as possible (so-called 'Sprint' missions) to minimize crew exposure to the zero-g and space radiation environment, to ease requirements on system reliability, and to enhance the probability of mission success." The short-stay missions tend to have long transit times and may not be the best option due to the relatively long exposure to zero-g and ionizing radiation. On the other hand the short-transit missions tend to have long stays on the surface requiring an adequate knowledge of the surface radiation environment to estimate risks and to design shield configurations. Our knowledge of the surface environment is theoretically based and suffers from an incomplete understanding of the physical interactions of GCR with the Martian atmosphere, Martian surface, and intervening shield materials. An important component of Mars surface robotic exploration is the opportunity to test our understanding of the Mars surface environment. The Mars surface environment is generated by the interaction of Galactic Cosmic Rays (GCR) and Solar Particle Events (SPEs) with the Mars atmosphere and Mars surface materials. In these interactions, multiple charged ions are reduced in size and secondary particles are generated, including neutrons. Upon impact with the Martian surface, the character of the interactions changes as a result of the differing nuclear constituents of the surface materials. Among the surface environment are many neutrons diffusing from the Martian surface and especially prominent are energetic neutrons with energies up to a few hundred MeV. Testing of these computational results is first supported by ongoing experiments at the Brookhaven National Laboratory but equally important is the validation to the extent possible by measurements on the Martian surface. Such measurements are limited by power and weight requirements of the specific mission and simplified instrumentation by necessity lacks the full discernment of particle type and spectra as is possible with laboratory experimental equipment. Yet, the surface measurements are precise and a necessary requisite to validate our understanding of the surface environment. At the very minimum the surface measurements need to provide some spectral information on the neutron environment. Of absolute necessity is the precise knowledge of the detector response functions for absolute comparisons between the computational model of the surface environment and the detector measurements on the surface.

Description: There are many similarities between the Mars Surveyor '01 (MS '01) landing site selection process and that of Mars Pathfinder. The selection process includes two parallel activities in which engineers define and refine the capabilities of the spacecraft through design, testing and modeling and scientists define a set of landing site constraints based on the spacecraft design and landing scenario. As for Pathfinder, the safety of the site is without question the single most important factor, for the simple reason that failure to land safely yields no science and exposes the mission and program to considerable risk. The selection process must be thorough, defensible and capable of surviving multiple withering reviews similar to the Pathfinder decision. On Pathfinder, this was accomplished by attempting to understand the surface properties of sites using available remote sensing data sets and models based on them. Science objectives are factored into the selection process only after the safety of the site is validated. Finally, as for Pathfinder, the selection process is being done in an open environment with multiple opportunities for community involvement including open workshops, with education and outreach opportunities.

Description: Mars Pathfinder, the first low-cost, quick Discovery class mission to be completed, successfully landed on the surface of Mars on July 4, 1997, deployed and navigated a small rover, and collected data from 3 science instruments and 10 technology experiments. The mission operated on Mars for 3 months and returned 2.3 Gbits of new data, including over 16,500 lander and 550 rover images, 16 chemical analyses of rocks and soil, and 8.5 million individual temperature, pressure and wind measurements. The rover traversed 100 m clockwise around the lander, exploring about 200 square meters of the surface. The mission captured the imagination of the public, and garnered front page headlines during the first week. A total of about 566 million internet "hits" were registered during the first month of the mission, with 47 million "hits" on July 8th alone, making the Pathfinder landing by far the largest internet event in history at the time. Pathfinder was the first mission to deploy a rover on Mars. It carried a chemical analysis instrument, to characterize the rocks and soils in a landing area over hundreds of square meters on Mars, which provided a calibration point or "ground truth" for orbital remote sensing observations. The combination of spectral imaging of the landing area by the lander camera, chemical analyses aboard the rover, and close-up imaging of colors, textures and fabrics with the rover cameras offered the potential of identifying rocks (petrology and mineralogy). With this payload, a landing site in Ares Vallis was selected because it appeared acceptably safe and offered the prospect of analyzing a variety of rock types expected to be deposited by catastrophic floods, which enabled addressing first-order scientific questions such as differentiation of the crust, the development of weathering products, and the nature of the early Martian environment and its subsequent evolution. The 3 instruments and rover allowed seven areas of scientific investigation: the geology and geomorphology of the surface, mineralogy and geochemistry of rocks and soils, physical properties of surface materials, magnetic properties of airborne dust, atmospheric science including aerosols, and rotational and orbital dynamics of Mars. Scientists were assembled into 7 Science Operations Groups that were responsible for requesting measurements by the 3 instruments, rover and engineering subsystems for carrying out their scientific investigations and for analyzing the data and reporting on their findings. The spacecraft was launched on December 4, 1996 and had a 7 month cruise to Mars, with four trajectory correction maneuvers. The vehicle entered the atmosphere directly following cruise stage separation. Parachute deployment, heatshield and lander separation, radar ground acquisition, airbag inflation and rocket ignition all occurred before landing at 2:58 AM true local solar time (9:56:55 AM PDT). The lander bounced at least 15 times up to 12 in high without airbag rupture, demonstrating the robustness of this landing system. Reconstruction of the final landing sequence indicates that the parachute/backshel1/1ander was tilted due to a northwest directed wind and wind shear, which resulted in the lander bouncing about I km to the northwest and initially downhill about 20 m from where the solid rockets fired. Two anomalously bright spots located in the lander scene are likely the heatshield, which continued in a ballistic trajectory about 2 km downrange (west southwest), and the backshell/parachute, which stayed nearer to where the rockets fired. Unconnected disturbed soil patches in the scene indicate that the final few bounces of the lander were from the east-southeast and were followed by a gentle roll to the west before coming to rest on the base petal. The location of the lander away from where the solid rockets fired and considerations of the exhaust products used to inflate the airbags and their fate, indicate that the Pathfinder landing system is one of the cleanest designed leaving the local area essentially contaminant free. The radio signal from the low-=gain antenna was received at 11:34 AM PDT indicating a successful landing.

Description: The Pathfinder Sojourner rover successfully acquired images that provided important and exciting information on the geology of Mars. This included the documentation of rock textures, barchan dunes, soil crusts, wind tails, and ventifacts. It is expected that the Marie Curie rover cameras will also successfully return important information on landing site geology. Critical to a proper analysis of these images will be a rigorous determination of rover location and orientation. Here, the methods that were used to compute rover position for Sojourner image analysis are reviewed. Based on this experience, specific recommendations are made that should improve this process on the '01 mission.

Description: Thunderstorms separate charge. Most places they lift positive charge or lower negative, a few places they lift negative or lower positive. The electrical generator is stronger in some parts of the cloud than in others. Our long term goal is to map this generator. Cloud physicists tell us that uncharged ice and water particles become charged by collision, and that the charge transferred depends on size, temperature and humidity. There is still some disagreement about exactly how the charge transferred depends on size, temperature, and humidity. In principle, if we knew this ice physics, and also knew the distribution of particles everywhere in the storm, and the winds everywhere and the temperature and humidity everywhere, then we could compute everywhere the electrical power of the thunderstorm generator. In practice it is difficult to know all these things, particularly the distribution of particles, so it is difficult to use real thunderstorms to falsify cloud electrification theories. We here take one small step towards computing that map of electrical generator power, by relating radar reflectivity profiles of 2000 storms to lightning flash rates of those storms. This small step by itself doesn't falsify any existing electrification theories; it merely places weak constraints on the relation of electric generator power to cloud ice.

Description: Two primary detection techniques (optical and RF) have a proven capability for detecting lightning from low earth orbit. However, the lightning processes that generate the optical and RF signals are vastly different providing significantly different information content from each sensor type. Because of the intervening ionosphere, low frequency RF components do not reach satellite altitudes. As a consequence, many of the processes associated with the major energy release of a lightning event (i.e. return strokes, k-changes, recoil streamers, etc), in all likelihood contribute little to the RF signal arriving at the satellite. The optical output from lighting, on the other hand, has been shown to be highly correlated with the energetic, charge-transferring processes mentioned above. On the down side, the optical energy, while essentially unaffected by the atmosphere once it emerges from the cloud, is heavily scattered within the cloud. While there is little absorption by the cloud, the great optical depth makes the total light energy emerging from the cloud to be dependent on where in the cloud the lightning occurred. Analyses suggest that when lightning is confined to the lowest regions of the cloud, the light is strongly attenuated and detection becomes problematic. Fortunately, the vast majority of lightning flashes are comprised of channels that propagate through the middle of the cloud and higher. These flashes produce bright signals at the top of a cloud and are readily detectable. Presently, we have two optical instruments in orbit. The Optical Transient Detector (OTD) has been orbiting the earth since April, 1995, while the Lightning Imaging Sensor (LIS) was launched on the Tropical Rainfall Measuring Mission (TRMM) in November of 1997. Both instruments are relatively small, solid state optical imagers, designed specifically to detect and locate lightning activity from low earth orbit with high detection efficiency and location accuracy.

Description: For the past century, scientists have made quantitative measurements of lightning discharges. In the process, they refined the definition of a lightning unit, or basic quantum of lightning, in order to base it on observable parameters. In this paper, we will use cluster analysis to derive a basic spatial and temporal definition or scale length for the unit of lightning. We will use data from three different systems that detected pulses from the same storm complex over Central Oklahoma during June, 1998. Since the different instruments detect lightning in different ways with different resolutions, there may not be a single definition of the unit of lightning that can be applied to all three systems. However, common components can be found since all instrumentation are detecting aspects of the same phenomenon.

Description: This presentation discusses the problem of local air quality as it is affected by modern aircraft engine exhaust and the objective of this workshop. It begins with a discussion on the nature and sources of particulates and aerosols. The problems, and the technical considerations of how to regulate the aircraft emissions, are reviewed. There is no local (i.e., state or county) regulations of the aircraft operations. Amongst the conclusions are: (1) there is an inadequate database of information regarding the emittants from aircrafts. (2) That data which does exist represents older engines and aircraft, it is not representative of the advanced and future fleet.

Description: Earth-based radar data remain an important part of the information set used to select and certify spacecraft landing sites on Mars. Constraints on robotic landings on Mars include: terrain elevation, radar reflectivity, regional and local slopes, rock distribution and coverage, and surface roughness, all of which are addressed by radar data. Indeed, the usefulness of radar data for Mars exploration has been demonstrated in the past. Radar data were critical in assessing the Viking Lander 1 site, and more recently, the Mars Pathfinder landing site.

Description: Over its 3,500 km length, Valles Marineris exhibits an enormous range of geologic and environmental diversity. At its western end, the canyon is dominated by the tectonic complex of Noctis Labyrinthus; while in the east it grades into an extensive region of chaos where scoured channels and streamlined islands provide evidence of catastrophic floods that spilled into the northern plains. In the central portion of the system, debris derived from the massive interior layered deposits of Candor and Ophir Chasmas spills into the central trough. In other areas, 6 km-deep exposures of Hesperian and Noachian-age canyon wall stratigraphy have collapsed in massive landslides that extend many tens of kilometers across the canyon floor. Ejecta from interior craters, aeolian sediments, and possible volcanics emanating from structurally controlled vents along the base of the scarps, further contribute to the canyon's geologic complexity. Following the initial rifting that gave birth to Valles Marineris, water appears to have been a principal agent in the canyon's geomorphic development an agent whose significance is given added weight by its potential role in both sustaining and preserving evidence of past life. In this regard, the interior layered deposits of Candor, Ophir, and Hebes Chasmas, have been identified as possible lucustrine sediments that may have been laid down in long-standing ice-covered lakes. The potential survival and growth of native organisms in such an environment, or in the aquifers whose disruption gave birth to the chaotic terrain and outflow channels to the north and east of the canyon, raises the possibility that fossil indicators of life may be present in the local sediment and rock. Because of the enormous distances over which these diverse environments occur, identifying a single landing site that maximizes the opportunity for scientific return is not a simple task. However, given the fluvial history and narrow geometry of the canyon, the presence of a single exit at its eastern end provides an opportunity for sampling that appears unequaled elsewhere in the system.

Description: It has been demonstrated during the past years that by its configuration, extended history of water ponding and sedimentary deposition, Gusev crater is one of the most favorable sites to consider for the incoming exploration of Mars. It provides exceptional possibilities to document the evolution of water, climate changes, and possibly the evolution of life on Mars through time. Because of all these reasons, it is probably one of the most interesting sites to target for sample return missions and human exploration, but as well, it is by all means an excellent target for the Surveyor '01, in spite of the current imposed mission constraints, as we propose to demonstrate.

Description: The NASA Ames' Center for Mars Exploration (CMEX) serves to coordinate Mars programmatic research at ARC in the sciences, in information technology and in aero-assist and other technologies. Most recently, CMEX has been working with the Institute for Human and Machine Cognition at the University of West Florida to develop a new kind of web browser based on the application of concept maps. These Cmaps, which are demonstrably effective in science teaching, can be used to provide a new kind of information navigation tool that can make web or CD based information more meaningful and more easily navigable. CMEX expects that its 1999 CD-ROM will have this new user interface. CMEX is also engaged with the Mars Surveyor Project Office at JPL in developing an Internet-based source of materials to support the process of selecting landing sites for the next series of Mars landers. This activity -- identifying the most promising sites from which to return samples relevant to the search for evidence of life -- is one that is expected to engage the general public as well as the science community. To make the landing site data easily accessible and meaningful to the public, CMEX is planning to use the IHMC Cmap browser as its user interface.

Description: The Thermal Emission Spectrometer (TES) instrument on the Mars Global Surveyor (MGS) mission has identified an accumulation of crystalline hematite (alpha-Fe2O3) that covers an area with very sharp boundaries approximately 350 by 350-750 km in size centered near 2 S latitude between 0 and 5 W longitude (Sinus Meridiani). The depth and shape of the hematite fundamental bands in the TES spectra show that the hematite is relatively coarse grained (〉 5-10 microns). The spectrally-derived areal abundance of hematite varies with particle size from approx. 10% for particles 〉 30 microns in diameter to 40-60% for unpacked 10 micron powders. The hematite in Sinus Meridiani is thus distinct from the fine-grained (diameter 〈 5-10 microns), red, crystalline hematite considered, on the basis of visible and near-IR data, to be a minor spectral component in Martian bright regions. A map of the hematite index has been constructed using TES data from 11 orbits, including the six in which hematite was detected and five orbits that passed nearby that showed no evidence of hematite. The boundaries of the hematite-rich region are sharp at spatial scales of about 10 km. Within this region there are spatial variations in spectral band depth of a factor of two to three. At the present time the hematite-rich region has not been completely mapped. However, by using the bounding orbits to the east and west in which hematite was not detected, we can establish that this region covers an area that is between 350 and 750 km in length and over -350 km in width (1.2 x 10(exp 5) to 2.6 x 10(exp 5 sq km). The hematite-rich surface discovered by TES closely corresponds with smooth-surfaced unit ('sm') that appears to be the surface of a layered sequence. The presence of small mesas superposed on 'sm' and the degraded nature of the small impact craters suggests that material has been removed from this unit. These layered materials do not appear to be primary volcanic products (i.e., lava flows) because there are no associated lava flow lobes, fronts or pressure ridges; there are no fissures or calderae, nor any other features that can be interpreted as volcanic within 'sm'. Bowl-shaped depressions in 'sm' and the remnant mesas on top of a portion of this unit suggest that deflation has removed material that was once above the present surface of 'sm'. The most likely cause of the deflation is wind, which suggests that the layered materials are relatively friable. In summary, Sinus Meridiani hematite is closely associated with a smooth, layered, friable surface that is interpreted to be sedimentary in origin.

Description: One of the goals of the Mars Pathfinder mission was to sample a diversity of rocks deposited by the Ares and Tiu Vallis floods. It was hoped that ancient highlands and younger lowlands material could be studied, as well as a diversity of rocks within these regions. Although Pathfinder found rocks that exhibited a number of textures and morphologies, several factors precluded the identification of a petrologic suite of rocks, if it was present. Namely among these were 1) The lack of geologic context for the rocks examined, 2) instrument limitations, and 3) pervasive dust and possible weathering finds. Based on the Pathfinder experience and incorporating recent results from Mars Global Surveyor and previous missions, two landing sites are proposed that can potentially overcome this problem and offer samples of ancient and recent Martian rock. The first site is at the dichotomy boundary, where ancient highlands and more recent lowlands meet. The second site is at the Ares Vallis headlands, where some of the source materials for the Pathfinder landing site may have been derived. Both of these sites meet the remote sensing and elevation constraints of the 2001 Lander mission but exhibit significant slopes and potential hazards in places. However, a properly placed ellipse can alleviate much of the concern, thereby offering two exciting sites that otherwise would not be chosen.

Description: Our Survey area comprises the Sinus Sabeus NW quadrangle that includes most of the Schiaparelli crater and part of the Arabia SW region (3 N to 15 S Lat.) and (0 to 337.5 W long.) and covers all regions that show a potential hydrogeological link with the Schiaparelli impact structure. This area is hereafter defined as the Schiaparelli Crater Region. The Schiaparelli crater region is one of the most documented MOC targets. Up to now, MGS MOC camera took two dozen images at an average of 5m/pxl resolution that not only provide an exceptional insight on the local geology and morphology, but give also key-elements to assess landing safety criteria. In addition, the MOLA topographic profile No. 23 passes through part of the crater basin allowing the adjustment of the elevation as previously known from the Viking mission (USGS I-2125, 1991). Beyond the Mars Polar Lander mission that will land next December, the future missions (2001 APEX, 2003, and 2005) are led by a series of science objectives and engineering constraints that must be considered in order to select landing sites that will fulfill the Surveyor Program's objectives. The search for a sound and safe candidate-site (without ending up with the usual "safe but boring" or "fascinating but too risky" site) is usually limited by the data available to the investigator, by the data accuracy (e.g. poor image resolution, poor altimetry), and the lack of crucial information for science and safety that can be derived from them. The Schiaparelli region provides an exception to this recurrent pattern. We listed the preliminary constraints for landing site selection identified for the Surveyor '01 mission, in terms of safety requirements and data needed and compared them against the existing information and/or data already available for the Schiaparelli region. The engineering constraints of '03 and '05 are not designated yet but, since they are also related to atmospheric density and Lander designs, we will assume that these points will be comparable to '01. The main difference will reside in the rover design, the Rocky-7 class rover being bigger than Marie Curie ('01) will be able to overcome bigger obstacles. We listed then the main objectives of the Surveyor Program and compared them with the potential offered by the Schiaparelli Crater Region to document them. Within the survey area, the Schiaparelli impact crater is 2.5 S/343.3 W (USGS 1-1376, MC-20 NW, 1981) and occupies a significant surface area. The crater has been proposed as a potential candidate-site in the past years. The purpose of this study is to show that, not only the Schiaparelli Crater would be a high-priority target, but that the region where it is located offer several very-high potential back-up sites, all within science and engineering constraints, that make this region probably the most promising candidate area so far.

Description: Wind and water vapor are two major factors driving the Earth's atmospheric circulation, and direct measurement of these factors is needed for better understanding of basic atmospheric science, weather forecasting, and climate studies. Coherent lidar has proved to be a valuable tool for Doppler profiling of wind fields, and differential absorption lidar (DIAL) has shown its effectiveness in profiling water vapor. These two lidar techniques are generally considered distinctly different, but this paper explores an experimental combination of the Doppler and DIAL techniques for measuring both wind and water vapor with an eye-safe wavelength based on a solid-state laser material. Researchers have analyzed and demonstrated coherent DIAL water vapor measurements at 10 micrometers wavelength based on CO2 lasers. The hope of the research presented here is that the 2 gm wavelength in a holmium or thulium-based laser may offer smaller packaging and more rugged operation that the CO2-based approach. Researchers have extensively modeled 2 um coherent lasers for water vapor profiling, but no published demonstration is known. Studies have also been made, and results published on the Doppler portion, of a Nd:YAG-based coherent DIAL operating at 1.12 micrometers. Eye-safety of the 1.12 micrometer wavelength may be a concern, whereas the longer 2 micrometer and 10 micrometer systems allow a high level of eyesafety.

Description: The Athena Precursor Experiment (APEX) is a suite of scientific instruments for the Mars Surveyor Program 2001 (MSP'01) lander. The major elements of the APEX pay load are: (1) Pancam/Mini-TES, a combined stereo color imager and mid-infrared point spectrometer. (2) An Alpha-Proton-X-Ray Spectrometer (APXS) for in-situ elemental analysis. (3) A Mossbauer Spectrometer for in-situ determination of the mineralogy of Fe-bearing rocks and soils. (4) A Magnet Array that can separate magnetic soil particles from non-magnetic ones.

Description: Triboelectric charging of nonconducting materials followed by sudden electrostatic discharge (ESD) can damage electronic equipment and become ignition hazard to combustible materials. Mars atmosphere has near zero humidity and therefore natural charge bleeding to surroundings is anticipated to be limited. Potential mitigation of ESD problems has been conjectured based upon strong extraterrestrial radiation on Mars compared to earth. A hypothesis was formulated that ESD problem is less significant in simulated Mars condition since strong radiation and presence of argon will generate an ionized environment; this will be conducive to rapid bleeding of static charge into the surroundings.

Description: The Mars Environmental Compatibility Assessment (MECA) will evaluate the Martian environment for soil and dust-related hazards to human exploration as part of the Mars Surveyor Program 2001 Lander. Sponsored by the Human Exploration and Development of Space (HEDS) enterprise, MECA's goal is to evaluate potential geochemical and environmental hazards that may confront future martian explorers, and to guide HEDS scientists in the development of high fidelity Mars soil simulants. In addition to objectives related to human exploration, the MECA data set will be rich in information relevant to basic geology, paleoclimate, and exobiology issues. The integrated MECA payload contains a wet-chemistry laboratory, a microscopy station, an electrometer to characterize the electrostatics of the soil and its environment, and arrays of material patches to study the abrasive and adhesive properties of soil grains. MECA is allocated a mass of 10 kg and a peak power usage of 15 W within an enclosure of 35 x 25 x 15 cm (figures I and 2). The Wet Chemistry Laboratory (WCL) consists of four identical cells that will accept samples from surface and subsurface regions accessible to the Lander's robotic arm, mix them with water, and perform extensive analysis of the solution. Using an array of ion-specific electrodes (ISEs), cyclic voltammetry, and electrochemical techniques, the chemistry cells will wet soil samples for measurement of basic soil properties of pH, redox potential, and conductivity. Total dissolved material, as well as targeted ions will be detected to the ppm level, including important exobiological ions such as Na, K+, Ca++, Mg++, NH4+, Cl, S04-, HC03, as well as more toxic ions such as Cu++, Pb++, Cd++, Hg++, and C104-. MECA's microscopy station combines optical and atomic-force microscopy (AFM) to image dust and soil particles from millimeters to nanometers in size. Illumination by red, green, and blue LEDs is augmented by an ultraviolet LED intended to excite fluorescence in the sample. Substrates were chosen to allow experimental study of size distribution, adhesion, abrasion, hardness, color, shape, aggregation, magnetic and other properties. To aid in the detection of potentially dangerous quartz dust, an abrasion tool measures sample hardness relative to quartz and a hard glass (Zerodur).

Description: Severe storms often have high flash rates (in excess of one flash per second) and are dominated by intracloud lightning activity. In addition to the extraordinary flash rates, there is a second distinguishing lightning characteristic of severe storms that seems to be important. When the total lightning history is examined, one finds sudden increases in the lightning rate, which we refer to as lightning "jumps," that precede the occurrence of severe weather by ten or more minutes. These jumps are typically 30-60 flashes/min, and are easily identified as anomalously large derivatives in the flash rate. This relationship is associated with updraft intensification and updraft strength is an important factor in storm severity (through the accumulation of condensate aloft and the stretching of vorticity). In several cases, evidence for diminishment of midlevel rotation and the descent of angular momentum from aloft is present prior to the appearance of the surface tornado. Based on our experience with severe and tornadic storms in Central Florida, we believe the total lightning may augment the more traditional use of NEXRAD radars and storm spotters. However, a more rigorous relation of these jumps to storm kinematics is needed if we are to apply total lightning in a decision tree that leads to improved warning lead times and decreased false alarm rates.

Description: The Lightning Imaging Sensor (LIS) is a NASA Earth Observing System (EOS) instrument on the Tropical Rainfall Measuring Mission (TRMM) platform designed to acquire and investigate the distribution and variability of total lightning (i.e., cloud-to-ground and intracloud) between q35' in latitude. Since lightning is one of the responses of the atmosphere to thermodynamic and dynamic forcing, the LIS data is being used to detect deep convection without land-ocean bias, estimate the precipitation mass in the mixed phased region of thunderclouds, and differentiate storms with strong updrafts from those with weak vertical motion.

Description: The Optical Transient Detector (OTD) is a space-based instrument specifically designed to detect and locate lightning discharges (intracloud and cloud-to-ground) as it orbits the Earth. A statistical examination of OTD lightning data reveals that nearly 1.2 billion flashes occurred over the entire earth during the one year period from September 1995 through August 1996. This translates to an average of 37 lightning flashes occurring around the globe every second, which is well below the traditional estimate of 100 flashes per second. An average of 75% of the global lightning activity during the year occurs between 30' S and 30' N. An analysis of the annual lightning distribution reveals that an average of 82% of the lightning flashes occur over the continents and 18% over the oceans, which translates to an average land-ocean flash density ratio of nearly 11.

Description: The lightning frequency model developed by Baker, Christian and Latham (1995) has been refined and extended, in an effort to provide a more realistic framework from which to examine computationally the relationships that might exist between lightning frequency f (which is now being routinely measured from satellites, using NASA/MSFC devices) and a variety of cloud physical parameters, including precipitation rate, updraught speed and non-precipitating ice content. Model results indicate the existence of a simple relationship between lightning frequency f and the upward flux of ice crystals into the thunderstorm anvil. It follows that, for a particular situation, one can assign a specific mass of non-precipitating ice to an individual lightning stroke. Therefore it may prove possible - using satellite measurements of global lightning - to estimate the atmospheric loading of ice crystals in thunderstorm anvils: a parameter of climatological importance. Early results from this work are presented, together with further studies of the relationships between f and other thundercloud parameters.

Description: A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.

Description: It is well known that most tropical cyclones (TCs) that make landfall along the Gulf coast of the United States spawn at least a few tornadoes. Although most landfalling TCs generate fewer than a dozen such tornadoes, a small proportion produce large swarm outbreaks, with as many as 25 or more tornadoes. Usually, these major outbreaks occur in large, intense hurricane-strength TCs, but on 15-17 August 1994 Tropical Storm Beryl spun off 37 tornadoes along its path from the Florida panhandle through the mid-Atlantic states. Some 32 of these tornadoes occurred on 16 August 1994 from eastern Georgia to southern Virginia, with most of these taking place in South Carolina. Beryl's 37 tornadoes moved it into what was at that time fifth place historically in terms of TC tornado productivity. The Beryl outbreak is especially noteworthy in that at least three of the tornadoes achieved peak intensity of F3 on the Fujita damage intensity scale. Although no fatalities resulted from the Beryl outbreak, at least 50 persons suffered injuries, and property damages totalled more than $50 million . The Beryl outbreak is a good example of a TC whose greatest danger to the public is its post-landfall severe weather. In this respect, and in the character of its swarm outbreak of tornadoes, it resembles another large tornado outbreak spawned by a relatively weak TC, Hurricane Danny of 1985). In the Danny outbreak, numerous shallow mini-supercell storms were found to have occurred, and it was noted that, because of the storms' relatively shallow depth, cloud-to-ground (CG) lightning was negligible. Better observations of future TC tornado outbreaks, especially with modern surveillance tools such as Doppler radars and the National Lightning Detection Network (NLDN), were recommended. Although the Beryl tornado outbreak is not the first set of TC-spawned tornado storms to be observed with the NLDN, it is one of the largest and likely the most intense such outbreak. The purpose of this paper is to document the NLDN-derived CG lightning characteristics of Beryl's tornadic storms, and to see how they compare with observations of CG lightning activity in other types of severe storms. In particular, we attempt to quantify the CG flash rates of TC tornadic cells, and to discover if there are any characteristics of their CG activity that may be useful to operational forecasters seeking to distinguish which cells are most likely to produce severe weather.

Description: The problem of retrieving ligntning, ground-strike location on a spherical Earth surface using a network of 4 or more time-of-arrival (TOA) sensors is considered, It is shown that this problem has an analytic solution and therefore does not require the use of nonlinear estimation theory (e.g., minimization). The mathematical robustness of the analytic solution is tested using computer-generated lightning sources and simulated TOA measurement errors. A summary of a quasi-analytic extension of the spherical Earth solution to an oblate spheroid Earth geometry is also provided.

Description: This study summarizes the results of an analysis of data from the LIS instrument on the TRMM platform. The data for the Indian summer monsoon season is examined to study the seasonal patterns of the geographic and diurnal distribution of lightning storms. The storms on the Tibetan plateau show a single large diurnal peak at about 1400 local solar time. A region of Northern Pakistan has two storm peaks at 0200 and 1400 local solar time. The morning peak is half the magnitude of the afternoon peak. The region south of the Himalayan Mountains has a combined diurnal cycle in location and time of storm occurrence.

Description: We have developed a new set of eight electric field mills that were flown on a NASA ER-2 high-altitude aircraft. During the Third Convection And Moisture EXperiment (CAMEX-3; Fall, 1998), measurements of electric field, storm dynamics, and ice microphysics were made over several hurricanes. Concurrently, the TExas-FLorida UNderflights (TEFLUN) program was being conducted to make the same measurements over Gulf Coast thunderstorms. Sample measurements are shown: typical flight altitude is 20km. Our new mills have an internal 16-bit A/D, with a resolution of 0.25V/m per bit at high gain, with a noise level less than the least significant bit. A second, lower gain channel gives us the ability to measure fields as high as 150 kV/m.

Description: The assignments and charges to the three workgroups are discussed. The three workgroups were: (1) Trace Chemistry, (2) Instrumentation, (3) Venues and procedures.

Description: We presented results from the SASS Near-Field Interactions Flight (SNIF-III) Experiment which was conducted during May and June 1997 in collaboration with the Vermont and New Jersey Air National Guard Units. The project objectives were to quantify the fraction of fuel sulfur converted to S(VI) species by jet engines and to gain a better understanding of particle formation and growth processes within aircraft wakes. Size and volatility segregated aerosol measurements along with sulfur species measurements were recorded in the exhaust of F-16 aircraft equipped with F-100 engines burning fuels with a range of fuel S concentrations at different altitudes and engine power settings. A total of 10 missions were flown in which F-16 exhaust plumes were sampled by an instrumented T-39 Sabreliner aircraft. On six of the flights, measurements were obtained behind the same two aircraft, one burning standard JP-8 fuel and the other either approximately 28 ppm or 1100 ppm S fuel or an equal mixture of the two (approximately 560 ppm S). A pair of flights was conducted for each fuel mixture, one at 30,000 ft altitude and the other starting at 35,000 ft and climbing to higher altitudes if contrail conditions were not encountered at the initial flight level. In each flight, the F-16s were operated at two power settings, approx. 80% and full military power. Exhaust emissions were sampled behind both aircraft at each flight level, power setting, and fuel S concentration at an initial aircraft separation of 30 m, gradually widening to about 3 km. Analyses of the aerosol data in the cases where fuel S was varied suggest results were consistent with observations from project SUCCESS, i.e., a significant fraction of the fuel S was oxidized to form S(VI) species and volatile particle emission indices (EIs) in comparably aged plumes exhibited a nonlinear dependence upon the fuel S concentration. For the high sulfur fuel, volatile particle EIs in 10-second-old-plumes were 2 to 3 x 10 (exp 17) / kg of fuel burned and exhibited no obvious trend with engine power setting or flight altitude. In contrast, about 8-fold fewer particles were observed in similarly aged plumes from the same aircraft burning fuel with 560 ppm S content and EIs of 1 x 10(exp 15)/ kg of fuel burned were observed in the 28 ppm S fuel case. Moreover, data recorded as a function of plume age indicates that formation and growth of the volatile particles proceeds more slowly as the fuel S level is reduced. For example, ultrafine particle concentrations appear to stabilize within 5 seconds after emission in the 1100 ppm S cases but are still increasing in 20-second old plumes produced from burning the 560 ppm S fuel.

Description: The mapping of the lightning optical pulses detected by the Lightning Imaging Sensor (LIS) is compared with the radiation sources by Lightning Detection and Ranging (LDAR) and the National Lightning Detection Network (NLDN) for three thunderstorms observed during and overpasses on 15 August 1998. The comparison involves 122 flashes including 42 ground and 80 cloud flashes. For ground flash, the LIS recorded the subsequent strokes and changes inside the cloud. For cloud flashes, LIS recorded those with higher sources in altitude and larger number of sources. The discrepancies between the LIS and LDAR flash locations are about 4.3 km for cloud flashes and 12.2 km for ground flashes. The reason for these differences remain a mystery.

Description: Since April 1995, lightning activity around the globe has been monitored with the Optical Transient Detector (OTD). The OTD observations acquired during the one year period from September 1995 through August 1996 have been used to statistically determine the number of flashes that occur over the Earth during each hour of the diurnal cycle, expressed both as a function of local time and universal time. The globally averaged local [il,htnina activity displays a peak in late afternoon (1500-1800 local time) and a minimum in the morning hours (0600- 1000 local time) consistent with convection associated with diurnal heating. No diurnal variation is found for oceanic storms. The diurnal lightning distribution (universal time) for the globe displays a variation of about 35% about its mean as compared to the Carnegie curve which has a variation of only 15% above and below the mean.

Description: Total lightning observations made by the Optical Transient Detector (OTD) of a tornadic thunderstorm that occurred over Oklahoma on 17 April 1995 are presented. The average flash rate of the tornadic storm during the 3.2 min observation period was 45 flashes/min, with a flash rate density of 1.16 x 10(exp -4)/s sq km. The total flash rate was almost 18 times higher than the cloud-to-ground rate measured by the National Lightning Detection Network (NLDN). In addition, total lightning rates were observed to decrease prior to tornadic development.

Description: In recent years, atmospheric conductivity and electric field measurements over thunderstorms have been made at 20 km with a high altitude aircraft. After compensating for the effects of aircraft charging induced by external electric fields no significant variations in ambient conductivity above thunderstorms have been found. These Gerdien results contrast strongly with the large (and frequent) conductivity variations reported in studies using relaxation probe techniques.

Description: The El Nino Southern Oscillation (ENSO) is a climate anomaly responsible for world-wide weather impacts ranging from droughts to floods. In the United States, warm episode years are known to produce above normal rainfall along the Southeast US Gulf Coast and into the Gulf of Mexico, with the greatest response observed in the October-March period of the current warm-episode year. The 1997-98 warm episode, notable for being the strongest event since 1982-83, presents our first opportunity to examine the response to a major ENSO event and determine the variation of wintertime thunderstorm activity in this part of the world. Due to the recent launch of a lightning sensor on NASA's Tropical Rainfall Measuring Mission (TRMM) in November 1997 and the expanded coverage of the National Lightning Detection Network (NLDN), we are able to examine such year-to-year changes in lightning activity with far greater detail than ever before.

Description: The overall focus of our research is to document long-term elevation change of the Greenland ice sheet using satellite altimeter data. In addition, we are investigating seasonal and interannual variations in the ice-sheet elevations to place the long-term measurements in context. Specific objectives of this research include: 1) Developing new techniques to significantly improve the accuracy of elevation-change estimates derived from satellite altimetry. 2) Measuring the elevation change of the Greenland ice sheet over a 10-year time period using Seasat (1978) and Geosat GM (1985-86) and Geosat ERM (1986-88) altimeter data. 3) Quantifying seasonal/interannual variations in the elevation-change estimates using the continuous time series of surface elevations from the Geosat GM and ERM datasets. 4) Extending the long-term elevation change analysis to two decades by incorporating data from the ERS-1/2 missions (1991-99) and, if available, the Geosat-Follow On (GFO) mission (1998-??).

Description: The Second Workshop on Stratospheric Models and Measurements Workshop (M&M II) is the continuation of the effort previously started in the first Workshop (M&M I, Prather and Remsberg [1993]) held in 1992. As originally stated, the aim of M&M is to provide a foundation for establishing the credibility of stratospheric models used in environmental assessments of the ozone response to chlorofluorocarbons, aircraft emissions, and other climate-chemistry interactions. To accomplish this, a set of measurements of the present day atmosphere was selected. The intent was that successful simulations of the set of measurements should become the prerequisite for the acceptance of these models as having a reliable prediction for future ozone behavior. This section is divided into two: model experiment and model descriptions. In the model experiment, participant were given the charge to design a number of experiments that would use observations to test whether models are using the correct mechanisms to simulate the distributions of ozone and other trace gases in the atmosphere. The purpose is closely tied to the needs to reduce the uncertainties in the model predicted responses of stratospheric ozone to perturbations. The specifications for the experiments were sent out to the modeling community in June 1997. Twenty eight modeling groups responded to the requests for input. The first part of this section discusses the different modeling group, along with the experiments performed. Part two of this section, gives brief descriptions of each model as provided by the individual modeling groups.

Description: The presence of ice in permanently shadowed depressions near the lunar poles and determination of its properties will significantly influence both the near- and long-term prospects for lunar exploration and development. Since data from the Lunar Prospector spacecraft indicate that water ice is likely present (the instrument measures hydrogen strongly suggests the presence of water), it is important to understand how to extract it for beneficial use, as well as how to preserve it for scientific analysis. Two types of processes can be considered for the extraction of water ice from the lunar poles. In the first case, energy is transported into the shadowed regions, ice is constrain models of impacts on the lunar surface and processed in-situ, and water is transported out of the cold trap. In the second case, ice-containing regolith can be mined in the cold trap, transported outside the cold trap, and the ice extracted in a location with abundant solar energy. A series of conceptual implementations has been examined and criteria have been developed for the selection of systems and subsystems for further study.

Description: The first microscopic sedimentological studies of the Martian surface will commence with the landing of the Mars Polar Lander (MPL) December 3, 1999. The Robotic Arm Camera (RAC) has a resolution of 25 um/p which will permit detailed micromorphological analysis of surface and subsurface materials. The Robotic Ann will be able to dig up to 50 cm below the surface. The walls of the trench will also be inspected by RAC to look for evidence of stratigraphic and / or sedimentological relationships. The 2001 Mars Lander will build upon and expand the sedimentological research begun by the RAC on MPL. This will be accomplished by: (1) Macroscopic (dm to cm): Descent Imager, Pancam, RAC; (2) Microscopic (mm to um RAC, MECA Optical Microscope (Figure 2), AFM This paper will focus on investigations that can be conducted by the RAC and MECA Optical Microscope.

Description: The '03-05 mission to Mars will include many of the elements already discussed for the '0 1 mission. The Athena payload has been adopted for the analysis and selection of samples, and the will include many of the same measurements to be performed during the '01 mission. In addition, the missions will include yet to be determined experiments to be done on or from the lander. Several groups are now competing for instruments and science to be done on the lander for both '03 and '05.

Description: The DART ("Dust Accumulation and Removal Test") package is an experiment which will fly as part of the MIP experiment on the Mars-2001 Surveyor Lander. Dust deposition could be a significant problem for photovoltaic array operation for long duration emissions on the surface of Mars. Measurements made by Pathfinder showed 0.3% loss of solar array performance per day due to dust obscuration. The DART experiment is designed to quantify dust deposition from the Mars atmosphere, measure the properties of settled dust, measure the effect of dust deposition on the array performance, and test several methods of mitigating the effect of settled dust on a solar array. Although the purpose of DART (along with its sister experiment, MATE) is to gather information critical to the design of future power systems on the surface of Mars, the dust characterization instrumentation on DART will also provide significant scientific data on the properties of settled atmospheric dust.

Description: The Mars Environmental Compatibility Assessment (MECA) is an instrument suite that will fly on the Mars Surveyor 2001 Lander Spacecraft. MECA is sponsored by the Human Exploration and Development of Space (HEDS) program and will evaluate potential hazards that the dust and soil of Mars might present to astronauts and their equipment on a future human mission to Mars. Four elements constitute the integrated MECA payload: a microscopy station, patch plates, an electrometer, and the wet chemistry laboratory (WCL). The WCL consists of four identical cells, each of which will evaluate a sample of Martian soil in water to determine conductivity, pH, redox potential, dissolved C02 and 02 levels, and concentrations of many soluble ions including sodium, potassium, magnesium, calcium and the halides. In addition, cyclic voltammetry will be used to evaluate reversible and irreversible oxidants present in the water/soil solution. Anodic stripping voltammetry will be used to measure concentrations of trace metals including lead, copper, and cadmium at ppb levels. Voltammetry is a general electrochemical technique that involves controlling the potential of an electrode while simultaneously measuring the current flowing at that electrode. The WCL experiments will provide information on the corrosivity and reactivity of the Martian soil, as well as on soluble components of the soil which might be toxic to human explorers. They will also guide HEDS scientists in the development of high fidelity Martian soil simulants. In the process of acquiring information relevant to HEDS, the WCL will assess the chemical composition and properties of the salts present in the Martian soil.

Description: Martian surface composition and processes are under study through analysis of spectral, magnetic and chemical data from Mars and analysis of laboratory analog materials. The focus of this study is on potential lander/rover measurements of weathered volcanic tephra and hydrothermal rocks because these samples resulted from processes that may have occurred on Mars. Fine-grained particles from these sources may be responsible for origination of the dust/soil on Mars that is shaping the planet's surface character. Alteration on the surface of Mars likely includes both chemical and physical interactions of soil particles and rock surfaces. Many of the minerals present in hydrothermal samples may be associated with organisms and may be useful as indicators of life or environments supportive of life on Mars. Characterization of the spectroscopic properties in the visible/near-infrared (VIS/NIR) and mid-infrared (IR) regions using reflectance, emittance and Raman, as well as the thermal properties of minerals thought to be present on Mars are being performed in order to identify them remotely. Particular interest is directed toward locating minerals, and hence landing sites, important to Astrobiology.

Description: The Mars Surveyor 2001 mission to Mars was initially a key element in the Mars sample return sequence of missions. A capable rover, carrying the Cornell Athena instruments would be placed on Mars to roam over several kilometers, select samples, and place them in a cache for return by a subsequent mission. Inevitably, budget constraints forced descopes. At one critical point, the landed payload consisted only of the HEDS (Human Exploration and Development of Space) payloads selected for testing environmental properties of the surface for future human exploration. Then Congress intervened and put back some of the funding that had been deleted. NASA next redefined the payload to include as many of the Athena instruments as possible, to be distributed between the lander deck and a Sojourner class rover. This payload would then be placed on a modified version of the Mars Polar Lander rather than on the much larger, and more expensive, lander that had been originally designed for the mission. With this functionality restored the '01 mission remains an important and pivotal element of the Mars Surveyor program. It completes the Mars Observer objectives with the gamma ray spectrometer mapping. This mission will largely complete the global characterization phase of Mars exploration and mark the beginning of focused surface exploration leading to return of the first samples and the search for evidence of past Martian life. MSP'01 also is the first mission in the combined Mars exploration strategy of the HEDS and Space Science Enterprises of NASA. This mission, and those to follow, will demonstrate technologies and collect environmental data that will provide the basis for a decision to send humans to Mars. The NASA exploration strategy for Mars includes orbiters, landers and rovers launched in 2001 and 2003 and a sample return mission to be launched in 2005, returning a sample by 2008. The purpose of the rovers is to explore and characterize sites on Mars. The 2003 and 2005 missions will select rocks, soil, and atmosphere for return to earth.

Description: Solid (soot) and liquid (presumed sulfate) particle emissions from aircraft engines may have serious impacts on the atmosphere. While the direct radiative impact of these particles is expected to be small relative to those from natural sources (Atmospheric Effects of Subsonic Aircraft: Interim Assessment of the Advanced Subsonic Technology Program, NASA Ref. Pub. 1400, 1997), their indirect effects on atmospheric chemistry and cloud formation may have a significant impact. The potential impacts of primary concern are the increase of sulfate surface area and accelerated heterogeneous chemical reactions, and the potential for either modified soot or sulfate particles to serve as cloud nuclei which would change the frequency or radiative characteristics of clouds. Volatile (sulfate) particle concentrations measured behind the Concorde aircraft in flight in the stratosphere were much higher than expected from near-field model calculations of particle formation and growth. Global model calculations constrained by these data calculate a greater level of stratospheric ozone depletion from the proposed High speed Civil Transport (HSCT) fleet than those without particle emission. Soot particles have also been proposed as important in heterogeneous chemistry but this remains to be substantiated. Aircraft volatile particle production in the troposphere has been shown by measurements to depend strongly on fuel sulfur content. Sulfate particles of sufficient size are known to provide a good nucleating surface for cloud growth. Although pure carbon soot is hydrophobic, the solid particle surface may incorporate more suitable nucleating sites. The non-volatile (soot) particles also tend to occupy the large end of aircraft particle size spectra. Quantitative connection between aircraft particle emissions and cloud modification has not been established yet, however, even small changes in cloud amount or properties could have a significant effect on the radiative balance of the atmosphere.

Description: The objectives of this work are to measure the ice discharge of the Greenland Ice Sheet close to the grounding line and/or calving front, and compare the results with mass accumulation and ablation in the interior to estimate the ice sheet mass balance.

Description: The primary constituents of the Earth's atmosphere are molecular nitrogen and molecular oxygen. Ozone is created when ultraviolet light from the sun photodissociates molecular oxygen into two oxygen atoms. The oxygen atoms undergo many collisions but eventually combine with a molecular oxygen to form ozone (O3). The ozone molecules absorb ultraviolet solar radiation, primarily in the wavelength region between 200 and 300 nanometers, resulting in the dissociation of ozone back into atomic oxygen and molecular oxygen. The oxygen atom reattaches to an O2 molecule, reforming ozone which can then absorb another ultraviolet photon. This sequence goes back and forth between atomic oxygen and ozone, each time absorbing a uv photon, until the oxygen atom collides with and ozone molecule to reform two oxygen molecules.

Description: We have selected four areas in Valles Marineris as potential landing sites for the 2001 mission. After 20 years of analyses, the formation of the Valles Marineris system of troughs and its associated deposits still has not been sufficiently explained. They could have formed by collapse, as tectonic grabens, or in two stages involving ancestral collapse basins later cut by grabens. Understanding all aspects of the Valles Marineris, in particular the interior layered deposits, would significantly contribute to deciphering the internal and external history of Mars. The deposits have been postulated to be remnants of wall rock, lacustrine deposits, mass wasting deposits, eolian deposits, carbonate deposits, or volcanic deposits. Because an understanding of the formation of Valles Marineris and its interior deposits is so important to deciphering the history of Mars, we have proposed landing sites for the 2001 mission on flat shelves of interior deposits in Melas Chasma.

Description: Our objective is to propose a landing site that the Mars Surveyor 2001 Lander and Curie Rover could go to on Mars that should meet the safety requirements of the spacecraft landing system and optimize surface operations (chiefly driven by power and communications requirements). This site lies between 1.5-3.5 deg S latitude, 195-198 deg W longitude, along a sharp albedo contact between the low-viscosity flow units of southern Elysium Planitia and the eroded highlands margin east of Aeolis Mensae. A relatively-bright "peninsula-like" protrusion of the eroded highlands into the south Elysium plains in this area reminds us of the head of an Ibis, and so we nickname this site "Ibishead Peninsula". This site is designed to be situated as close to a diversity of geologic units within view of the lander instruments. Based on our experience with the visibility of horizon details from the Mars Pathfinder and Viking landing sites, we stipulate that for horizon features to be resolved suitably for detailed study from the lander, they must be no more than several kilometers distant. This is so that diversity can be placed in a geologic context in a region that we feel has some exciting science potential. This objective is different from the Mars Pathfinder requirement to land at a site with a maximum chance for containing a diversity of rocks within a few tens of meters of the lander, which resulted in the selection of a "grab bag" site.

Description: One of the greatest unresolved issues concerns the evolution of Mars early in its history; during the time period that accretion was winding down but the frequency of impacting debris was still heavy. Ancient cratered terrain that has only been moderately modified since the period of heavy bombardment covers about a quarter of the planet's surface but the environment during its formation is still uncertain. This terrain was dominantly formed by cratering. But unlike on the airless Moon, the impacting craters were strongly modified by other contemporary surface processes that have produced distinctive features such as 1) dendritic channel networks, 2) rimless, flatfloored craters, 3) obliteration of most craters smaller than a few kilometers in diameter (except for post heavy-bombardment impacts), and 4) smooth intercrater plains. The involvement of water in these modification processes seems unavoidable, but interpretations of the surface conditions on early Mars range from the extremes of 1) the "cold" model which envisions a thin atmosphere and surface temperatures below freezing except for local hydrothermal springs; and 2) the "warm" model, which invokes a thick atmosphere, seasonal temperatures above freezing in temperate and equatorial regions, and at least occasional precipitation as part of an active hydrological cycle. The nature of hydrologic cycles, if they occurred on Mars, would have been critically dependent on the environment. The resolution of where along this spectrum the actual environment of early Mars occurred is clearly a major issue, particularly because the alternate scenarios have much different implications about the possibility that life might have evolved on Mars.

Description: Regions near Apollinaris Patera are proposed for consideration as Mars Surveyor landing sites. Gulick (1998) proposed this region at the First Mars Surveyor Landing Site workshop; Bulmer and Gregg (1998) provided additional support. Apollinaris Patera is situated on the highlands/lowlands boundary at 8.5S, 186W. The volcano itself has been mapped as Hesperian in age. The regions surrounding Apollinaris show evidence for volcanism, volcano-ice interactions, and erosion by water. Numerous valleys modified by fluvial processes dissect a large fan structure emanating from the southern flank of the volcano. Sapping valleys have formed along the southern terminus of the fan structure. Regions near Apollinaris Patera provide a unique opportunity to sample outcrop lithologies ranging from highland Noachian basement rocks, to Hesperian aged lava flows, channel and flood plain materials, to Amazonian volcanic, ash and channel deposits.

Description: Over the past year and a half, the Center for Mars Exploration (CMEX) at NASA Ames Research Center (ARC) has been working with the Mars Surveyor Project Office at JPL to promote interactions among the planetary community and to coordinate landing site activities for the Mars Surveyor Project Office. To date, CMEX has been responsible for organizing the first two Mars Surveyor Landing Site workshops, web-archiving resulting information from these workshops, aiding in science evaluations of candidate landing sites, and serving as a liaison between the community and the Project. Most recently, CMEX has also been working with information technologists at Ames to develop a state-of-the-art collaborative web site environment to foster interaction of interested members of the planetary community with the Mars Surveyor Program and the Project Office. The web site will continue to evolve over the next several years as new tools and features are added to support the ongoing Mars Surveyor missions.

Description: The Isidis basin rim may be key to understanding Mars' past with future lander missions: this area enables the mission objective to explore Mars' climatic and geologic history, including the search for liquid water and evidence of prior or extant life in ancient terrains. While two safe candidate landing sites for Mars Pathfinder were identified in Isidis Planitia, and one is being pursued for the Mars Surveyor 2001 Lander [Crumpler: 3.4 N, 277.8 W], the region around Isidis Planitia, in contrast to Tharsis for example, has only been lightly studied. The advent of new high resolution data sets provides an opportunity to reassess the geologic context of this impact basin and its rim within the Martian geologic sequence as a candidate site for studying Mars' ancient cratered terrain and ancient hydrosphere. This reexamination is warranted by the various hypotheses that Isidis was once filled with ice or water.

Description: There are many similarities between the Mars Surveyor '01 (MS '01) landing site selection process and that of Mars Pathfinder. The selection process includes two parallel activities in which engineers define and refine the capabilities of the spacecraft through design, testing and modeling and scientists define a set of landing site constraints based on the spacecraft design and landing scenario. As for Pathfinder, the safety of the site is without question the single most important factor, for the simple reason that failure to land safely yields no science and exposes the mission and program to considerable risk. The selection process must be thorough and defensible and capable of surviving multiple withering reviews similar to the Pathfinder decision. On Pathfinder, this was accomplished by attempting to understand the surface properties of sites using available remote sensing data sets and models based on them. Science objectives are factored into the selection process only after the safety of the site is validated. Finally, as for Pathfinder, the selection process is being done in an open environment with multiple opportunities for community involvement including open workshops, with education and outreach opportunities.

Description: Of the areas that meet the engineering criteria for MSP 01, only two are coincident with magnetic anomalies measured by the MAG/ER instrument on MGS. Area A is centered on about 10 deg S, 202 deg W and extends from about 7.5 deg S to 15 S. This area is associated with three bands of magnetic anomalies, two with positive values surrounding an area with negative values. Area B corresponds with a circular high positive magnetic anomaly and is centered at 13.5 deg S, 166 deg W. In addition to magnetic anomalies, the proposed sites have other attributes that make then attractive from of standpoint of meeting the objectives of the Mars Program. The landing site candidates meet the engineering requirements outlined on the Mars '01 landing site page htip://mars.jpl.nasa.gov/2001/landingsite. These are (source of data in parentheses): latitude between 3 deg N and 12 deg S, rock abundance between 5-10% (IRTM), fine-component thermal inertia 〉 4 cgs units (IRTM), topography 〈 2.5 km (MOLA). There are three exceptions: 1) Area B contains sites that lie up to about 15 deg S, 2) some sites are considered that have rock abundance values of 3-13%. 3) High resolution Viking coverage may not be available. These exceptions will be noted.

Description: The primary role of models in the assessment process is to predict changes to ozone. It is crucial therefore that the ability of the models to reproduce the actual distribution of ozone be tested. Historically, maps of the ozone column (latitude by month) have been used for this purpose. In MM I a climatology was developed for the vertical distribution of ozone for 15-60 km, based on SBUV data for 1979-80. SBUV profiles are reported with vertical resolution of approx. 5 km, but the true resolution is lower, approx. 8 km above the ozone maximum and approx. 15 km for 10-25 km. The climatology was considered valid to about 20-30% at 20 km and to 50% at 15 km. Comparisons were made with models in mixing ratio (ppm), which emphasizes the middle and upper stratosphere. A new ozone climatology was developed for the vertical distribution of ozone for MM II. Our goal was to develop a product that could be used to evaluate models in the lower stratosphere, the region where most of the ozone column resides and where most of the ozone loss is occurring, as well as the middle and upper stratosphere.

Description: The rationale for looking for prokaryote fossils in Martian materials is based on our present understanding of the environmental evolution of that planet in comparison to the history of the terrestrial environments and the development and evolution of life on Earth. On Earth we have clear, albeit indirect, evidence of life in 3.8 b.y.-old rocks from Greenland and the first morphological fossils in 3.3-3.5 b.y.-old cherts from South Africa and Australia. In comparison, Mars, being smaller, probably cooled down after initial aggregation faster than the Earth. Consequently, there could have been liquid water on its surface earlier than on Earth. With a similar exogenous and endogenous input of organics and life-sustaining nutrients as is proposed for the Earth, life could have arisen on that planet, possibly slightly earlier dm it did on Earth. Whereas on Earth liquid water has remained at the surface of the planet since about 4.4 b.y. (with some possible interregnums caused by planet-sterilising impacts before 3.8. b.y. and perhaps a number of periods of a totally frozen Earth, this was not the case with Mars. Although it is not known exactly when surficial water disappeared from the surface, there would have been sufficient time for life to have developed into something similar to the terrestrial prokaryote stage. However, given the earlier environmental deterioration, it is unlikely that it evolved into the eukaryote stage and even evolution of oxygenic photosynthesis may not have been reached. Thus, the impetus of research is on single celled life simnilar to prokaryotes. We are investigating a number of methods of trace element analysis with respect to the Early Archaean microbial fossils. Preliminary neutron activation analysis of carbonaceous layers in the Early Archaean cherts from South Africa and Australia shows some partitioning of elements such as As, Sb, Cr with an especial enrichment of lanthanides in a carbonaceous-rich banded iron sediment . More significantly, preliminary TOF-SIMS investigations of organics in the cherts reveals the presence of a biomarker, which appears to be a derivative of bacterial polymer, in the carbonaceous parts of the rocks. We conclude that a combination of morphological, isotope and biogeochemical methods can be used to successfully identify signs of life in terrestrial material, and that these methods will be useful in searching for signs of life in extraterrestrial materials.

Description: The 13 samples from Mars identified in the terrestrial meteorite collections vary from dunite to pyroxenite to microgabbro or basalt. All of these rocks appear to have formed from primitive melts with similar major element compositional characteristics; i.e., FeO-rich and Al2O3-Poor melts relative to terrestrial basalt compositions. Although all of the SNC rocks can be derived by melting of the same Al-depleted mantle, contamination of SNC's by a Rb-enriched mantle or crustal source is required to explain the different REE characteristics of SNC rocks. Thus, there are indications of an old crustal rocktype on Mars, and this rock does not appear to have been sampled. This paper focuses primarily on the composition of the SNC basalts, however, and on the compositions of rocks which could be derived from SNC basaltic melt by magmatic processes. In particular, we consider the possible compositions which could be achieved through accumulation of early-formed crystals in the SNC primitive magma. Through a set of experiments we have determined (1) melt (magma) compositions which could be produced by melt evolution as crystals are removed from batches of this magma cooling at depth, and (2) which evolved (Si02enriched, MgO-depleted) rock compositions could be produced from the SNC magma, and how these compare with the Pathfinder andesite composition. Finally, we compare the SNC magma compositions to the Mars soil composition in order to determine whether any source other than SNC is required.

Description: The Mars Surveyor 2001 Project consists of two missions to Mars, an Orbiter and a Lander, both to be launched in the spring of 2001 for October 2001 (Orbiter) and January 2002 (Lander) arrival at Mars. The Orbiter will support the Lander mission primarily as a communications relay system; the Lander will not have direct-to-Earth communications capability. Science data collected from the Orbiter will also be used to aid in the geologic interpretation of the landing site, along with data from past missions. Combining the Orbiter and Lander missions into a single Project has enabled the streamlining of many activities and an efficient use of personnel and other resources at the Jet Propulsion Laboratory and at the spacecraft contractor, Lockheed Martin Astronautics.

Description: The MINUTES instrument of the Athena Precursor Experiment (APEX) on the Mars Surveyor 2001 lander mission will perform the first thermal infrared remote sensing observations from the surface of another planet. Experience gained from this experiment will be used to guide observations from identical instruments mounted on the Athena rovers, to be launched in 2003 and 2005. The utility of infrared spectrometers in determining the mineralogic composition of geologic surfaces from airborne and spaceborne platforms has been amply demonstrated. However, relatively little experience exists in using functionally similar instruments on the ground in the context of planetary science. What work has been done on this problem has mostly utilized field spectrometers that are designed to look down on nearby target rocks. While many Mini-TES observations will be made with this type of geometry, it is likely that other observations will be made looking horizontally at the more vertically-oriented facets of rock targets, to avoid spectral contamination from dust mantles. On rover missions, the Mini-TES may also be pointed horizontally at rocks several meters away, to determine if they are worthy of approaching for in situ observations and possible sample cacheing. While these observations will undoubtedly prove useful, there are important, and perhaps unappreciated, differences between horizontal-viewing, surface-based spectroscopy and the more traditional nadir-viewing, orbit or aircraft-based observations. Plans also exist to step the Mini-TES in a rastering motion to build hyperspectral scenes. Horizontal viewing hyperspectral cubes also possess unique qualities that call for innovative analysis techniques. The effect of viewing geometry: In thermal emission spectroscopy, regardless of whether an instrument is looking down on or horizontally at a target, the same basic equation governs the radiance reaching the sensor .

Description: In a previous publication, we proposed the formation of caves at mega and microscale on Mars and emphasized their potential for the exobiology exploration. The recent MOC images have shown promising indicators that caves are actually existing on Mars. In the first section, we develop the theoretical potential formation of martian caves. Then, we show how MOC is supporting this hypothesis of their formation and the new types of environments it suggests. The existence of caves on Mars from microscale to microscale structures can be predicted according to the Mars geological and climatic history. A first global approach is to consider caves as a result of underground water activity combined with tectonic movement. They can be formed by: (1) diversion of channel courses in underground conduits; (2) fractures of surface drainage patterns; chaotic terrain and collapsed areas in general; (4) seepage face in valley walls and/or headwaters; (5) inactive hydrothermal vents and lava tubes.

Description: The primary objective of the Thermal Emission Imaging System (THEMIS) on the Mars Surveyor '01 Orbiter is to study the composition of the Martian surface at high spatial resolution. THEMIS will map the surface mineralogy using multi-spectral thermal infrared images in 8 spectral bands from 6.5 to 14.5 microns. In addition, a band centered at 15 microns will be used to map atmospheric temperatures and provide an important aid in separating the surface and atmospheric components. The entire planet will be mapped at 100 m resolution within the available data volume using a multi-spectral, rather than hyperspectral, imaging approach. THEMIS will also acquire 20 m resolution visible images in up to 5 spectral bands using a replica of the Mars 98 Orbiter (MARCI) and Lander (MARDI) cameras. Over 15,000 panchromatic (3,000 5-color), 20 x 20 km images will be acquired for morphology studies and landing site selection. The thermal-infrared spectral region contains the fundamental vibrational absorption bands of most minerals which provide diagnostic information on mineral composition. All geologic materials, including carbonates, hydrothermal silica, sulfates, phosphates, hydroxides, silicates, and oxides have strong absorptions in the 6.5-14.5 micron region. Silica and carbonates, which are key diagnostic minerals in thermal spring deposits, are readily identified using thermal-IR spectra. In addition, the ability to identify all minerals allows the presence of aqueous minerals to be interpreted in the proper geologic context. An extensive suite of studies over the past 35 years has demonstrated the utility of vibrational spectroscopy for the quantitative determination of mineralogy and petrology. The fundamental vibrations within different anion groups, such as C03, S04, P04, and SiO4, produce unique, well separated spectral bands that allow carbonates, sulfates, phosphates, silicates, oxides, and hydroxides to be readily identified. Additional stretching and bending modes involving major cations, such as Mg, Fe, Ca, and Na, allow Further mineral identification, such as the excellent discriminability of minerals within the silicate and carbonate groups.

Description: In winter, active convective clouds frequently form along the coastline of the Hokuriku district, in association with strong advection of Siberian air masses over the Sea of Japan. On the other hand, in summer, many thunderclouds form in the Kanto region in the afternoon every day. Summer and winter thunderclouds were investigated by field works, operation of the C- and X-band weather radars and a car-borne fieldmill. The investigation found a very close relation between the temporal variation of 3-dimensional radar echo and surface electric field magnitude detected by a car-borne fieldmill in the case of summer thunderclouds and winter convective clouds or thunderclouds. The study probed the close relation among radar echoes, quantity of thunderclouds and surface electric field magnitude in the summer and winter seasons. We think that summer thundercloud activity can basically be equated with winter thundercloud lightning activity, except that the magnitude of surface electric field under summer thunderclouds in the case of the Kanto region cannot be equated with that under winter thunderclouds in the case of the Hokuriku district in winter.

Description: A six year record of optical observations of lightning-induced mesospheric transient luminous events (TLEs) is available from the Yucca Ridge Field Station (YRFS) near Ft. Collins, CO. Climatological analyses reveal sprites and elves occur in a variety of convective storm types, but principally mesoscale convective systems (MCSs) and squall lines. Severe supercell storms rarely produce TLEs, except during their dissipating stage. Few TLEs are observed during storms with radar echo areas 〈7,500 sq km. Above this size there is a modest correlation with radar areal coverage. A typical High Plains storm produces 45 TLEs over a 143 interval. Sprites and most elves are associated with +CGs. The probability of a TLE increases with peak current. In six storms, 5.1% of +CGs produced TLEs, the number increasing to 32% of +CGs with 〉75 kA and 52% of +CGs with 〉100 kA peak current.

Description: Significant differences are known to exist on a global scale between continental and oceanic total lightning regional flash rates, suggesting differences in the properties of convective storms in these regimes. Lightning properties observed by the Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) over land and ocean are compared, limited to analysis over the tropics in order to simplify physical interpretation. We find that the mean flash rates of individual storms over tropical land only exceed those over ocean by a factor of 2 (far less than the observed differences in regional flash rates). However, the average nearest neighbor distance of continental thunderstorms is half that over oceans. Cloud-top lightning optical radiance in oceanic storms is also twice as large as over land, suggesting either more energetic flashes over the oceans or less intervening cloud particles.

Description: The Sampling Procedures and Venues Workgroup discussed the potential venues available and issues associated with obtaining measurements. Some of the issues included Incoming Air Quality, Sampling Locations, Probes and Sample Systems. The following is a summary of the discussion of the issues and venues. The influence of inlet air to the measurement of exhaust species, especially trace chemical species, must be considered. Analysis procedures for current engine exhaust emissions regulatory measurements require adjustments for air inlet humidity. As a matter of course in scientific investigations, it is recommended that "background" measurements for any species, particulate or chemical, be performed during inlet air flow before initiation of combustion, if possible, and during the engine test period as feasible and practical. For current regulatory measurements, this would be equivalent to setting the "zero" level for conventional gas analyzers. As a minimum, it is recommended that measurements of the humidity and particulates in the incoming air be taken at the start and end of each test run. Additional measurement points taken during the run are desirable if they can be practically obtained. It was felt that the presence of trace gases in the incoming air is not a significant problem. However, investigators should consider the ambient levels and influences of local air pollution for species of interest. Desired measurement locations depend upon the investigation requirements. A complete investigation of phenomenology of particulate formation and growth requires measurements at a number of locations both within the engine and in the exhaust field downstream of the nozzle exit plane. Desirable locations for both extractive and in situ measurements include: (1) Combustion Zone (Multiple axial locations); (2) Combustor Exit (Multiple radial locations for annular combustors); (3) Turbine Stage (Inlet and exit of the stage); (4) Exit Nozzle (Multiple axial locations downstream of the nozzle). Actual locations with potential for extractive or non-intrusive measurements depend upon the test article and test configuration. Committee members expressed the importance of making investigators aware of various ports that could allow access to various stages of the existing engines. Port locations are engine si)ecific and might allow extractive sampling or innovative hybrid optical-probe access. The turbine stage region was one the most desirable locations for obtaining samples and might be accessed through boroscope ports available in some engine designs. Discussions of probes and sampling systems quickly identified issues dependent on particular measurement quantities. With general consensus, the group recommends SAE procedures for measurements and data analyses of currently regulated exhaust species (CO2, CO, THC, NO(x),) using conventional gas sampling techniques. Special procedures following sound scientific practices must be developed as required for species and/or measurement conditions not covered by SAE standards. Several issues arose concerning short lived radicals and highly reactive species. For conventional sampling, there are concerns of perturbing the sample during extraction, line losses, line-wall reactions, and chemical reactions during the sample transport to the analyzers. Sample lines coated with quartz.or other materials should be investigated for minimization of such effects. The group advocates the development of innovative probe techniques and non-intrusive optical techniques for measurement of short lived radicals and highly reactive species that cannot be sampled accurately otherwise. Two innovative probe concepts were discussed. One concept uses specially designed probes to transfer optical beams to and from a region of flow inaccessible by traditional ports or windows. The probe can perturb the flow field but must have a negligible impact on the region to be optically sampled. Such probes are referred to as hybrid probes and are under development at AEDC for measurement in the high pressure, high temperature of a combustor under development for power generation. The other concept consists of coupling an instrument directly to the probe. The probe would isolate a representative sample stream, freeze chemical reactions and direct the sample into the analyzer portion of the probe. Thus, the measurement would be performed in situ without sample line losses due either to reactions or binding at the wall surfaces. This concept was used to develop a fast, in situ, time-of-flight mass spectrometer measurement system for temporal quantification of NO in the IMPULSE facility at AEDC. Additional work is required in this area to determine the best probe and sampling technique for each species measurement requirement identified by the Trace Chemistry Working Group. A partial list of Venues was used as a baseline for discussion. Additional venues were added to the list and the list was broken out into the following categories: (1)Engines (a) Sea Level Test Stands (b) Altitude Chambers; (2) Annular Combustor Test Stands, (3) Sector Flametube Test Stands, (4) Fundamentals Rigs/Experiments.

Description: The danger of natural and triggered lightning significantly impacts space launch operations supported by the USAF. The lightning Launch Commit Criteria (LCC) are used by the USAF to avoid these lightning threats to space launches. This paper presents a brief overview of the LCC.

Description: Although the importance of aerosols and their precursors are now well recognized, the characterization of current subsonic engines for these emissions is far from complete. Furthermore, since the relationship of engine operating parameters to aerosol emissions is not known, extrapolation to untested and unbuilt engines necessarily remains highly uncertain. 1997 NASA LaRC engine test, as well as the parallel 1997 NASA LaRC flight measurement, attempts to address both issues by expanding measurements of aerosols and aerosol precursors with fuels containing different levels of fuel sulfur content. The specific objective of the 1997 engine test is to obtain a database of sulfur oxides emissions as well as the non-volatile particulate emission properties as a function of fuel sulfur and engine operating conditions. Four diagnostic systems, extractive and non-intrusive (optical), will be assembled for the gaseous and particulate emissions characterization measurements study. NASA is responsible for the extractive gaseous emissions measurement system which contains an array of analyzers dedicated to examining the concentrations of specific gases (NO, NO(x), CO, CO2, O2, THC, SO2) and the smoke number. University of Missouri-Rolla uses the Mobile Aerosol Sampling System to measure aerosol/particulate total concentration, size distribution, volatility and hydration property. Air Force Research Laboratory uses the Chemical Ionization Mass Spectrometer to measure SO2, SO3/H2SO4, and HN03 Aerodyne Research, Inc. uses Infrared Tunable Diode Laser system to measure SO2, SO3, NO, H2O, and CO2.

Description: The goals of the trace chemistry group were to identify the processes relevant to aerosol and aerosol precursor formation occurring within aircraft gas turbine engines; that is, within the combustor, turbine, and nozzle. The topics of discussion focused on whether the chemistry of aerosol formation is homogeneous or heterogeneous; what species are important for aerosol and aerosol precursor formation; what modeling/theoretical activities to pursue; what experiments to carry out that both support modeling activities and elucidate fundamental processes; and the role of particulates in aerosol and aerosol precursor formation. The consensus of the group was that attention should be focused on SO2, SO3, and aerosols. Of immediate concern is the measurement of the concentration of the species SO3, SO2, H2SO4 OH, HO2, H2O2, O, NO, NO2, HONO, HNO3, CO, and CO2 and particulates in various engines, both those currently in use and those in development. The recommendation was that concentration measurements should be made at both the combustor exit and the engine exit. At each location the above species were classified into one of four categories of decreasing importance, Priority I through IV, as follows: Combustor exit: Priority I species - SO3:SO2 ratio, SO3, SO2, and particulates; Priority II species: OH and O; Priority III species - NO and NO2; and Priority IV species - CO and CO2. For the Engine exit: Priority I species - SO3:SO2 ratio, SO3, SO2,H2SO4, and particulates; Priority II species: OH,HO2, H2O2, and O; Priority III species - NO, NO2, HONO, and HNO3; and Priority IV species - CO and CO2. Table I summarizes the anticipated concentration range of each of these species. For particulate matter, the quantities of interest are the number density, size distribution, and composition. In order to provide data for validating multidimensional reacting flow models, it would be desirable to make 2-D, time-resolved measurements of the concentrations of the above species and, in addition, of the pressure, temperature, and velocity. A near term goal of the experimental program should be to confirm the nonlinear effects of sulfur speciation, and if present, to provide an explanation for them. It is also desirable to examine if the particulate matter retains any sulfur. The recommendation is to examine the effects on SOx production of variations in fuel-bound sulfur and aromatic content (which may affect the amount of particulates formed). These experiments should help us to understand if there is a coupling between particulate formation and SO, concentration. Similarly, any coupling with NOx can be examined either by introducing NOx into the combustion air or by using fuel-bound nitrogen. Also of immediate urgency is the need to establish and validate a detailed mechanism for sulfur oxidation/aerosol formation, whose chemistry is concluded to be homogeneous, because there is not enough surface area for heterogeneous effects. It is envisaged that this work will involve both experimental and theoretical programs. The experimental work will require, in addition to the measurements described above, fundamental studies in devices such as flow reactors and shock tubes. Complementing this effort should be modeling and theoretical activities. One impediment to the successful modeling of sulfur oxidation is the lack of reliable data for thermodynamic and transport properties for several species, such as aqueous nitric acid, sulfur oxides, and sulfuric acid. Quantum mechanical calculations are recommended as a convenient means of deriving values for these properties. Such calculations would also help establish rate constants for several important reactions for which experimental measurements are inherently fraught with uncertainty. Efforts to implement sufficiently detailed chemistry into computational fluid dynamic codes should be continued. Zero- and one-dimensional flow models are also useful vehicles for elucidating the minimal set of species and reactions that must be included in two- and three-dimensional modeling studies.

Description: This paper reviews the relationships of the programs and projects and reviews the purpose of the Engine Exhaust Trace Chemistry (EETC) Committee. The charges of the Committee are: (1) to prioritize the engine trace constituents for assessing impacts of aircraft; (2) Assess both extractive and insitu measurement techniques; and (3) Determine the best venues for performing the necessary measurements. A synopsis of evidence supporting and questions concerning the role(s) of aerosol/particulates was presented. The presentation also reviewed how sulfur oxidation kinetics interactions in the hot-section and nozzle play a role in the formation of aerosol precursors. The objective of the workshop, and its organization is reviewed.

Description: Charged aerosol clouds allow to create strong electric fields which generate discharges. A character of appearance and development of the discharges is similar to thundercloud processes. That is why the charged aerosol clouds are used for experiments on studying of discharges in air. Experimental data on electromagnetic fields investigation produced by discharges between charged cloud and ground are considered.

Description: One of the original objectives of the Mars Orbiter Camera (MOC), as proposed in 1985, was to acquire observations to be used in assessing future spacecraft landing sites. Images obtained by the Mars Global Surveyor MOC since March 1999 provide the highest resolution views (1.5-4.5 m/pixel) of the planet ever seen. We have been examining these new data to develop a general view of what Mars is like at meter-scale within the latitudes and elevations that are accessible to the Mars Surveyor 2001 lander. Our goal is to provide guidance to the 2001 landing site selection process, rather than to use MOC images to recommend a specific landing site.

Description: Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.

Description: Artificial gravity (AG), as a means of preventing physiological deconditioning of astronauts during long-duration space flights, presents certain special challenges to the otolith organs and the adaptive capabilities of the CNS. The key issues regarding the choice of AG acceleration, radius, and rotation rate are reviewed from the viewpoints of physiological requirements and human factors disturbances. Head movements and resultant Coriolis forces on the rotating platform may limit the usefulness of economical short centrifuges for other than brief periods of intermittent stimulation.

Description: In 1996-1997 an experiment with super dwarf wheat (Greenhouse-2) was made aboard the orbital complex MIR as a part of the MIR-NASA space science program. The article deals with the main production and morphometric characteristics of plants that completed their vegetation cycle in the space flight. Lengths of the whole cycle of vegetation and its individual stages were essentially same as in ground control experiments. Dry mass of one plants equal, the number of headed shoots was in 2.7 times less in the flight harvest as compared with the control. The height of shoots was reduced by one half. No seeds were found in the heads formed in space. The architecture of heads was substantially different from what had been observed in the preceeding ground control experiments: mass of the heads was halved and lengths of inflorescence and palea awn shortened. The number of spikelets in a head reduced up to 8-10 vs. 13-14 in the controls, whereas the number of florets per a spikelet averaged 5 vs. 3 in the controls. The experiments showed that mainly the most profound changes in the productive and morphometric parameters of the super dwarf wheat plants were largely caused by the phytotoxic effects of ethylene rather than spaceflight specific factors as its concentrations in the MIR air amount to 0.3-1.8 mg/m3.

Description: A suite of protein and nonprotein amino acids were detected with high-performance liquid chromatography in the water- and acid-soluble components of an interior fragment of the Martian meteorite Nakhla, which fell in Egypt in 1911. Aspartic and glutamic acids, glycine, alanine, beta-alanine, and gamma-amino-n-butyric acid (gamma-ABA) were the most abundant amino acids detected and were found primarily in the 6 M HCl-hydrolyzed, hot water extract. The concentrations ranged from 20 to 330 parts per billion of bulk meteorite. The amino acid distribution in Nakhla, including the D/L ratios (values range from 〈0.1 to 0.5), is similar to what is found in bacterially degraded organic matter. The amino acids in Nakhla appear to be derived from terrestrial organic matter that infiltrated the meteorite soon after its fall to Earth, although it is possible that some of the amino acids are endogenous to the meteorite. The rapid amino acid contamination of Martian meteorites after direct exposure to the terrestrial environment has important implications for Mars sample-return missions and the curation of the samples from the time of their delivery to Earth.

Description: As the twentieth century closes, retrospectives cite the Apollo moon missions as one of the important events of the past 100 years. A trip to Mars, however, would be even more challenging and significant. A round-trip Mars journey would require nearly three years away from Earth, a significant leap in complexity compared to the two week long Moon trips or the record-breaking fourteen-month flight on Mir. What would be the physiologic and medical challenges of a Mars flight? Two key areas of physiology present the greatest potential problems--calcium metabolism and radiation exposure. Data from Mir missions show that bone loss continues in space despite an aggressive countermeasure program. Average losses were 0.35% per month, but some load bearing areas lost 〉1% per month. A 1% loss rate, if it continued unabated for 30 months, could produce osteoporosis. Smaller losses could still increase fracture risk. Some bone loss can be well tolerated, particularly if the bone can be regained after the mission. But the effectiveness of post-flight rehabilitation to restore the density and quality of bone after spaceflight is not well known. Bone loss estimates are based on continuous weightlessness exposure, but this is not a requirement for a Mars trip. Most of the time on a Mars trip will be spent in the 1/3 Earth's gravity environment on Mars, and either intermittent or continuous artificial gravity can be provided for the transit between planets (although at an engineering cost). The dosing of the gravity exposure (e.g. the level and duration), however, has not been established. Radiation protection also requires a balance between engineering cost and human health. Excessive shielding could add billions of dollars to the cost of a mission. Trips in interplanetary space, however, expose the crew to heavy high-energy particles from cosmic rays (HZE particles), which have a high linear energy transfer. This high energy leads to significant biological damage (e.g. chromosomal aberrations, cancer induction). A recent report from the Committee on Space Biology and Medicine notes that only one systematic study of cancer induction from high-energy particles has been conducted (using the mouse Harderian gland). Predictions of cancer risk and acceptable radiation exposure in space are extrapolated from minimal data. Other areas of physiology also present problems, such as muscle loss, cardiovascular deconditioning, and vestibular adaptation. Despite all the issues, however, a focussed, aggressive research program that uses the resources of the International Space Station should pave the way for mankind's greatest adventure--a trip to Mars.

Description: Observations of the gravity field of Mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes. The rough, elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near-isostatic compensation, whereas the smooth, low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south. The northern hemisphere shows evidence for buried impact basins, although none large enough to explain the hemispheric elevation difference. The gravitational potential signature of Tharsis is approximately axisymmetric and contains the Tharsis Montes but not the Olympus Mons or Alba Patera volcanoes. The gravity signature of Valles Marineris extends into Chryse and provides an estimate of material removed by early fluvial activity.

Description: A comparison of laboratory spectra with Galileo data indicates that hydrated sulfuric acid is present and is a major component of Europa's surface. In addition, this moon's visually dark surface material, which spatially correlates with the sulfuric acid concentration, is identified as radiolytically altered sulfur polymers. Radiolysis of the surface by magnetospheric plasma bombardment continuously cycles sulfur between three forms: sulfuric acid, sulfur dioxide, and sulfur polymers, with sulfuric acid being about 50 times as abundant as the other forms. Enhanced sulfuric acid concentrations are found in Europa's geologically young terrains, suggesting that low-temperature, liquid sulfuric acid may influence geological processes.

Description: The ability of living organisms to survive on the smaller bodies in our solar system is examined. The three most significant sterilizing effects include ionizing radiation, prolonged extreme vacuum, and relentless thermal inactivation. Each could be effectively lethal, and even more so in combination, if organisms at some time resided in the surfaces of airless small bodies located near or in the inner solar system. Deep within volatile-rich bodies, certain environments theoretically might provide protection of dormant organisms against these sterilizing factors. Sterility of surface materials to tens or hundreds of centimeters of depth appears inevitable, and to greater depths for bodies which have resided for long periods sunward of about 2 A.U.

Description: Data from both 27 sites in the Atlanta mesonet surface meteorological network and eight National Weather Service sites were analyzed for the period from 26 July to 3 August 1996. Analysis of the six precipitation events over the city during the period (each on a different day) showed that its urban heat island (UHI) induced a convergence zone that initiated three of the storms at different times of the day, i.e., 0630,0845, and 1445 EDT. Previous analysis has shown that New York City (NYC) effects summer daytime thunderstorm formation and/or movement. That study found that during nearly calm regional flow conditions the NYC UHI initiates convective activity. Moving thunderstorms, however, tended to bifurcate and to move around the city, due to its building barrier effect. The current Atlanta results thus agree with the NYC results with respect to thunderstorm initiation.

Description: Analyses of satellite, ground-based, and balloon measurements allow updated estimates of trends in the vertical profile of ozone since 1979. The results show overall consistency among several independent measurement systems, particularly for northern hemisphere midlatitudes where most balloon and ground-based measurements are made. Combined trend estimates over these latitudes for the period 1979-96 show statistically significant negative trends at ail attitudes between 10 and 45 km, with two local extremes: -7.4 +/- 2.0% per decade at 40 km and -7.3 +/- 4.6% per decade at 15 km attitude. There is a strong seasonal variation in trends over northern midlatitudes in the altitude range of 10 to 18 km, with the largest ozone loss during winter and spring. The profile trends are in quantitative agreement with independently measured trends in column ozone, the amount of ozone in a column above the surface. The vertical profiles of ozone trends provide a fingerprint for the mechanisms of ozone depletion over the last two decades.

Description: We take advantage of the May 1998 biomass burning event in Southern Mexico to test the global applicability of a smoke aerosol size model developed from data observed in South America. The Mexican event is an unique opportunity to observe well-aged, residual smoke. Observations of smoke aerosol size distribution made from vertical profiles of airborne in situ measurements show an inverse relationship between concentration and particle size that suggests the aging process continues more than a week after the smoke is separated from its fire sources. The ground-based radiometer retrievals show that the column-averaged, aged, Mexican smoke particles are larger (diameter = 0.28 - 0.33 micrometers) than the mean smoke particles in South America (diameter = 0.22 - 0.30 micrometers). However, the difference (delta - 0.06 micrometer) translates into differences in backscattering coefficient of only 4-7% and an increase of direct radiative forcing of only 10%.

Description: The SASS (Subsonic Assessment) Ozone and NO(x) Experiment (SONEX) was an airborne field campaign conducted in October-November 1997 in the vicinity of the North Atlantic Flight Corridor Lo study the impact of aircraft emissions on NOx and ozone (03). A fully instrumented NASA DC-8 aircraft was used as the primary SONEX platform. SONEX activities were closely coordinated with the European POLINAT-2 (Pollution from Aircraft Emissions in the North Atlantic Flight Corridor) program, which used a Falcon-20 aircraft and an instrumented in-service Swissair B-747. Both campaigns focused on the upper troposphere/"lowermost" stratosphere (UT/LS) as the region of greatest interest. Specific sampling goals were achieved with the aid of a state-of-the art modeling and meteorological support system, which allowed targeted sampling of air parcels with desired characteristics. A substantial impact of aircraft emissions on NO(x) and O3 in the UT/LS of the study region is shown to be present. It is further shown that the NO(x)- HO(x)-O3 relationships are highly nonlinear and must be accurately simulated to make meaningful future predictions with global models. SONEXIPOLINAT-2 results are being published in Special Sections of GRL and JGR. Here we provide a brief overview of SONEX design, implementation, and expected results to provide a context within which these publications can be understood.

Description: An analysis of nadir reflectivity Fourier spatial power spectra and autocorrelation functions at solar wavelengths and for cloudy conditions has been carried out. The data come from Landsat Thematic Mapper (TM) observations, while Monte Carlo (MC) simulations are used to aid the interpretation of the Landsat results. We show that radiative processes produce consistent signatures on power spectra and autocorrelation functions. The former take a variety of forms not shown or explained in previous observational studies. We demonstrate that the TM spectra can potentially be affected by both radiative "roughening" at intermediate scales (approx. 1 -5 km), being more prevalent at large solar zenith angles, and the already documented radiative "smoothing" at small scales (less than 1 km). These processes are wavelength dependent, as shown by systematic differences between conservative (for cloud droplets) TM band 4 (approx. 0.8 microns) and absorbing band 7 (approx. 2.2 microns): band 7 exhibits more roughening and less smoothing. This is confirmed quantitatively by comparing least-squared fitted power spectral slopes for the two bands. It is also corroborated by a slower decrease with distance of autocorrelation function values for band 4 compared to band 7. The appearance of roughening at large solar zenith angles is a result of side illumination and shadowing and adds an additional complexity to the power spectra. MC spectra are useful in illustrating that scale invariant optical depth fields can produce complex power spectra that take a variety of shapes under different conditions. We show that radiative roughening increases with the decrease of single scattering albedo and with the increase of solar zenith angle (as in the observations). For high Sun there is also a clear shift of the radiative smoothing scale to smaller values as droplet absorption increases. The shape of the power spectrum is sensitive to the magnitude and type of cloud top height variability, with the spectral signatures of decorrelation between reflectance and optical depth at large scales becoming stronger as the magnitude of cloud top variations increase. Finally, the usefulness of power spectral analysis in evaluating the skill of novel optical depth retrieval techniques in removing 3D radiative effects is demonstrated. New techniques using inverse Non-local Independent Pixel Approximation (NIPA) and Normalized Difference of Nadir Reflectivity (NDNR) yield optical depth fields which better match the scale-by-scale variability of the true optical depth field.