ALBERT

Description: The main purpose of the Halogen Lamp Experiment (HALEX) was to investigate the operation of a halogen lamp during an extended period in a microgravity environment and to prove its behavior in space. The Mirror Heating Facilities for Crystal Growth and Material Science Experiments in space relies on one or two halogen lamps as a furnace to melt the specimens. The HALEX aim is to verify: full power operation of a halogen lamp for a period of about 60 hours; achievement of about 10% of its terrestrial life span; and operation of the halogen lamp under conditions similar to furnace operation.

Description: Some of the design problems that are now being addressed in consideration of a microcontroller for the upcoming GAS payload are discussed. Microcontrollers will be used to run the experiments and to collect and store the data from those experiments. Some of the requirements for a microcontroller are to be small, lightweight, have low power consumption, and high reliability. Some of the solutions that were developed to meet these design requirements are discussed. At present, the experiment is still in the design stage and the final design may change from what is presented here. The search for new integrated circuits which will do all that is needed all in one package continues.

Description: Airborne Imaging Spectrometer data from Mono Lake, California, were studied in order to establish spectral radiance of test areas under solar illumination. The objective is to provide a method of atmospheric correction for major absorbers from the spectrometer data themselves. Crucial to the analysis is radiometric calibration of the instrument. Good agreement is found between calculated and measured radiances for uniform surface targets (beaches), but simulations of atmospheric properties with LOWTRAN lead to unreasonably low values of atmospheric precipitable water. Absorptions from carbon dioxide are not detected in the AIS data, but are strongly present in the LOWTRAN model. The apparent low contrast of all atmospheric absorption bands leads to a study of contamination from overlapping spectral orders in the AIS data. The suspected contamination is shown unambiguously to be present beyond approximately 1500 nm and consists of an extra radiance term including atmospheric bands from the delta/2 wavelength interval. A rigorous removal of the unwanted spectral contamination does not seem possible for any data taken in the rock mode. Rough estimates for tree-mode observations might be pieced together is a suitable after-the-fact radiometric claibration of the instrument can be formulated.

Description: An Infrared Camera was built for astronomical observations and for testing arrays for satellite based work. The detectors are sensitive to mid infrared wavelengths. The camera was tested at the University of Arizona 61 and 90 inch telescopes and the NASA IRTF. These tests have demonstrated a sensitivity consistent with photon shot noise with an approximately 10% quantum efficiency for each pixel when the camera was used with a 1.6% spectral filter or when used with a Fabry-Perot having a resolving power of 2000. Initial measurements of read out noise, dark current, cross talk, and hysteresis were made. The detector chip in current use is a hybrid array manufactured by the Hughes Aircraft Company. Because part of the goal was to develop and advance technology, it was decided to work with a switched MOSFET array. This architecture is very promising, and the detector parameters will be quantified carefully.

Description: Preliminary results from the Hughes 58 x 62 gallium-doped silicon infrared array are presented. The device functioned predictably and repeatedly at the low temperatures for the Space Infrared Telescope Facility (SIRTF). Power dissipation was reduced to acceptable levels while still maintaining the device speed. The infrared response was excellent and the degree of anomalous effects was compatible to conventional photoconductors.

Description: The fabrication of antimony doped silicon (Si:Sb) detector arrays are described for use in 30 micron infrared imaging applications. The operation of the multiplexer readout circuit which will be used for this application is also described.

Description: The initial testing performed on the Hughes Metal Oxide Semiconductor Direct Readout (MOS DRO) with a Si:In extrinsic infrared array is described. The testing to date was of a screening nature and the results are primarily qualitative rather than quantitative. At a later date the performance optimization phase will be initiated. An encouraging result is that this response is strongly dependent on the detector temperature, to the extent that thermal transients introduced during the chip readout will affect the performance. A responsivity of 1 A/W at 2.2 microns with a bias of 15 volts, which is well below what is optimum bias, was obtained.

Description: A description of the design and performance of an imaging spectrometer intended for operation in the 7 to 14 micron wavelength range is presented. It is based upon a 16 by 16 element Si:Bi hybrid array, a circular variable filter wheel, and a microcomputer data acquisition system. The spatial-spectral photometric performances were evaluated in the laboratory as well as field tested at astronomical observatories. The performance characteristics of the system are presented as well as laboratory and astronomical images.

Description: Hybrid silicon Infrared Charge Coupled Devices (IRCCDs) are evaluated for use as viable astronomical detectors. A Si:In photoconductor array which is bump-bonded to a silicon multiplexer is described. A summary of the device parameters is given.

Description: The general architecture of the imaging array, some merits of HgCdTe-on-sapphire as a detector material, and the current status of the laboratory tests and the Short Wave Infrared (SWIR) camera are described.

Description: Highlights of the results obtained on arsenic-doped silicon blocked impurity band (BIB) detectors and arrays since the invention of the BIB concept a few years ago are presented. After a brief introduction and a description of the BIB concept, data will be given on single detector performance. Then different arrays that were fabricated will be described and test data presented.

Description: The 32 x 32 HgCdTe array manufactured by Rockwell International was proven to be a highly competitive detector type for use at wavelengths shorter than 2.5 microns. The goal of a K=+16 sky survey using this array attached to the Steward Observatory Transit Telescope is clearly within reach. The detector material exhibits high quantum efficiency and low dark currents indicating that its usefulness may extend beyond its use with a CCD readout on groundbased telescopes.

Description: In infrared astronomy observations, one of the key detector performance parameters is the dark current which, together with the optics, establishes the fundamental limit of a space-based instrument. This technical note summarizes an effort to measure dark current performance of the MLA/Short Wave Infrared photovoltaic HgCdTe array (2.5 micron cutoff) at temperatures from 65 to 120 K. The preliminary results indicate that dark current decreased systematically to 100 K, then the value became measurement-limited at about 3.0 E-18 A/pixel, or 19 electrons/sec/pixel.

Description: A program of testing aimed at the evaluation of systems that have the potential to provide the level of performance required for use in space-based instruments was undertaken and their usefulness appraised for astronomy. The results of the first phase of the program to characterize selected pixels of a HgCdTe photovoltaic array detector were reported.

Description: The Infrared Space Observatory (ISO), an approved and funded project of the European Space Agency (ESA), will be an astronomical satellite observatory operating at wavelengths from 3 to 200 microns. The ISO Project and its status are summarized. The overall goals are outlined, the scientific instruments are described, and the current activities are summarized.

Description: The Infrared Space Observatory (ISO) satellite will contain a 60 cm telescope. A 4 faces pyramid mirror feeds each experiment with a 3 arc minute part of the telescope field of view. The camera system is described. The arrays for the 3 to 5 and 5 to 17 micron channel are also discussed.

Description: Experience gained in operating infrared detector arrays for high sensitivity astronomical applications at the University of Rochester are summarized. Progress made in operating the 32 x 32 InSb array with bump-bonded Silicon CCD readout is described. Astronomical work done with the 32 x 32 camera is also described. Plans for the future, including improvements for the 32 x 32 camera system as well as implementing a new generation of 58 x 62 InSb array using switched-MOSFET direct readout multiplexing system in the place of the older CCD technology is discussed.

Description: Bolometers are still the detectors of choice for low background infrared observations at wavelengths longer than 200 microns. In the low background limit, bolometers become more sensitive as their operating temperature decreases, due to fundamental thermodynamic laws. The adiabatic demagnetization technique was evaluated by building a bolometer detection system operating at a wavelength of 1 millimeter for use at a ground based telescope. The system was fit checked at the telescope and is expected to take its first data in November, 1985.

Description: Photovoltaic indium antimonide (PV InSb) detector technology has matured over the past several years to enable a wide variety of applications to use this high-performance detector material to advantage. The operating conditions for most of the applications to date for back-side illuminated PV InSb arrays have encompassed focal plane temperatures ranging from 40 to approximately 95 K, with the majority in the narrower range between 60 and 80 K. Background flux conditions have ranged from 10 to the 10th power ph/sq cm/sec to 10 to the 16th power ph/sq cm/sec, most typically between 10 to the 12th power and 10 to the 14th power ph/sq cm/sec. Appropriately, the array parameters were optimized for maximum performance over these temperature and background ranges. The key parameters which were peaked in this process were the resistance-area product of the detectors and their quantum efficiency. The Space Infrared Telescope Facility (SIRTF) Infrared Array Camera requirements, however, present very low temperature and background operating conditions, plus the need for very high signal to noise ratios. Preliminary analysis indicates that back-side illuminated PV InSb arrays can be optimized for operation under these conditions, and some performance projections will be presented.

Description: Bolometer elements were built and tested using NTD germanium and ion-implanted Si thermometer elements. The thermal links were made using aluminum wires and NbC(x)N(y) coated carbon fibers. The temperature dependence of the detector resistance, lead thermal conductivity, and heat capacity were measured. The dependence of the detector resistance on applied electric field was also measured. This, combined with the current-voltage curve for the detector, allowed the calculation of the detector responsivity. Known amounts of energy were deposited into the detector by allowing X-rays from the decay of Fe-55 to be thermalized in the detector. In the best-measured case, the predicted pulse height/measured height was 1.04 + or - .05. The noise at frequencies above 25 Hz in the NTD Ge was near that predicted by thermodynamics. The noise below 25 Hz has a 1/f character and may be in the carbon fiber/bolometer junction. The implanted detectors show some 1/f noise which depends on the total thermometer volume. Comparison between noise measurements and theory will be presented.

Description: The first IR Detector Technology Workshop took place at NASA Ames Research Center on July 12 and 13, 1983. The conclusions presented at that meeting are still valid. More was learned about the physics of hopping conduction at very low temperatures which will be important for bolometer design and operation at ever decreasing temperatures. Resistivity measurements were extended down to 50 mK. At such low temperatures, precise knowledge of the neutron capture cross sections sigma (sub n) of the various Ge isotopes is critical if one is to make an accurate prediction of the dopant concentrations and compensation, and therefore resistivity, that will result from a given irradiation. An empirical approach for obtaining the desired resistivity material is described and the process of conducting a set of experiments which will improve the knowledge of the effective sigma (sub n) values for a given location in a particular reactor is discussed. A wider range of NTD Ge samples is now available. Noise measurements on bolometers with ion implanted contacts show the no 1/f noise component appears down to 1 Hz and probably lower.

Description: Ge:Be photoconductors were optimized for the 30 to 50 micron wavelength range. Crystal growth of detector quality material requires good control of both the Be and residual impurity doping. Detective quantum efficiencies of n sub d = 46% at 5 A/W were achieved at a photon background of 10 to the 8th power p/s. The responsivity of Ge:Be detectors can be strongly temperature-dependent when the residual shallow levels in the material are closely compensated. Transient responses on the order of approximately 1 second were observed in some materials. The role of residual shallow impurities on the performance of photoconductors doped with semi-deep and deep impurities is discussed.

Description: One of the four focal plane instruments of the Infrared Space Observatory (ISO) is ISOPHOT, a photopolarimeter for the wavelength region 3 to 200 microns. Each experiment occupies a quadrant of the focal plane. The telescope beam is directed into each experiment by means of a pyramid mirror and by tilting the satellite. The diameter of the unvignetted field of view is 3 arcmin or 7.85 mm in the focal plane (1 mm = 23 arcsec). The temperatures provided are 3 K for cooling the detector systems and 8 K for the experiment structure. Available detectors are described along with the current status of the experiment.

Description: A new approach to infrared detector readout has appeared with the development of integrating JFET amplifiers. This brief progress report includes results on the operation of commercially available devices at a temperature of 40 K, on their sensitivity and on an effort to develop a new JFET with properties optimized for cryogenic applications. Even with presently available devices it will be shown that for applications such as the Space Infrared Telescope Facility (SIRTF), the most strigent sensitivity requirements of noise currents as low as 1 electron/sec in less than 100 seconds of integration can be met.

Description: The Space Infrared Telescope Facility (SIRTF) is envisioned as a next generation space observatory for observations between 2 and 700 microns. In order to address many of the important scientific questions in areas such as cosmology, star formation, and galaxy evolution, infrared detectors of unparalleled sensitivity will be required. Dark current measurements are described for a number of different discrete photoconductive detectors that may be of importance at the very low backgrounds expected with SIRTF.

Description: Requirements for background-limited (BLIP) detectors are discussed in terms of number of photons falling on each pixel, dark current, high detective quantum efficiencies, large numbers of pixels, and array size.

Description: The Space Shuttle Challenger was observed spectroscopically in two passes over Maui during the Spacelab 2 mission. Through most of one of the passes strong bands centered at 1.52 and 1.69 microns, tentatively identified as OH bands, were detected. The average luminosity of the Shuttle in the 1.45 to 1.75 micron range was roughly equal to that of a star of magnitude +5.5. The luminosity was much lower during part of the pass. Spectra from 0.65 to 2.4 microns were obtained during the second pass. These showed that most of the nonthermal emission is in the 1.2 to 2.2 micron range as would be expected for vibrationally excited OH.

Description: Airborne Imaging Spectrometer (AIS) data were collected 30 August 1985 from a desert shrub community in central Oregon. Spectra from artificial targets placed on the test site and from bare soil, big sagebrush (Artemesia tridentata wyomingensis), silver sagebrush (Artemesia cana bolander), and exposed volcanic rocks were studied. Spectral data from grating position 3 (tree mode) were selected from 25 ground positions for analysis by Principal Factor Analysis (PFA). In this grating position, as many as six factors were identified as significant in contributing to spectral structure. Channels 74 through 84 (tree mode) best characterized between-class differences. Other channels were identified as nondiscriminating and as associated with such errors as excessive atmospheric absorption and grating positin changes. The test site was relatively simple with the two species (A. tridentata and A. cana) representing nearly 95% of biomass and with only two mineral backgrounds, a montmorillonitic soil and volcanic rocks. If, as in this study, six factors of spectral structure can be extracted from a single grating position from data acquired over a simple vegetation community, then AIS data must be considered rich in information-gathering potential.

Description: Airborne Imaging Spectrometer (AIS) data were acquired over an area of freshwater wetlands in Central California on September 23, 1985. Plant samples were subsequently collected along the flight line with the goal of relating plant tissue chemistry to spectral reflectance in the near-infrared region. It was determined that a consistent relationship existed between spectral response and plant tissue chemistry. This was especially evident in the 1500 to 1700 nm region.

Description: Airborne Imaging Spectrometer (AIS) data were acquired in 1985 over the Bonanza Creek Experimental Forest, Alaska for the analysis of canopy characteristics including biochemistry. Concurrent with AIS overflights, foliage from fifteen coniferous and deciduous forest stands were analyzed for a variety of biochemical constituents including nitrogen, lignin, protein, and chlorophyll. Preliminary analysis of AIS spectra indicates that the wavelength region between 1450 to 1800 namometers (nm) displays distinct differences in spectral response for some of the forest stands. A flat field subtraction (forest stand spectra - flat field spectra) of the AIS spectra assisted in the interpretation of features of the spectra that are related to biology.

Description: Airborne Imaging Spectrometer (AIS) data were collected over the fossil hot spring deposit at Ivanhoe, Nevada in order to determine the surface distribution of NH4-bearing minerals. Laboratory studies show that NH4-bearing minerals have characteristic absorption features in the near-infrared (NIR). Ammonium-bearing feldspars and alunites were observed at the surface of Ivanhoe using a hand-held radiometer. However, first look analysis of the AIS images showed that the line was about 500 m east of its intended mark, and the vegetation cover was sufficiently dense to inhibit preliminary attempts at making relative reflectance images for detection of ammonium minerals.

Description: The Airborne Imaging Spectrometer (AIS) was flown over granitic, volcanic, and calc-silicate terrain around the Mary Kathleen Uranium Mine in Queensland, in a test of its mineralocial mapping capabilities. An analysis strategy and restoration and enhancement techniques were developed to process the 128 band AIS data. A preliminary analysis of one of three AIS flight lines shows that the data contains considerable spectral variation but that it is also contaminated by second-order leakage of radiation from the near-infrared region. This makes the recognition of expected spectral absorption shapes very difficult. The effect appears worst in terrains containing considerable vegetation. Techniques that try to predict this supplementary radiation coupled with the log residual analytical technique show that expected mineral absorption spectra can be derived. The techniques suggest that with additional refinement correction procedures, the Australian AIS data may be revised. Application of the log residual analysis method has proved very successful on the cuprite, Nevada data set, and for highlighting the alunite, linite, and SiOH mineralogy.

Description: The Singatse Range is composed of a series of 53 types of volcanic, plutonic, metamorphic, and sedimentary rocks. In addition the Jurassic plutonic rocks are also of economic interest for their copper mineralization which is contained in a porphyry dike swarm. The 1984 and 1985 flight results from the Airborne Imaging Spectrometer (AIS) instrument flown in the NASA/JPL C-130 aircraft are contrasted and compared. The 1984 data are less noisy than the 1985, in which many sets of vertical stripings from bad detectors can be seen. Significantly however, enough of the hydrothermal alteration patterns can be seen in each line at the mutual crossing points that one can say that the specific targets were detected in both year's flights. The spectra of both years are corrupted by the second-order effect from the grating, but 0-H bond absorption at essentially correct wavelengths for sericite and/or kaolinite can be seen.

Description: The surface mineralogy in and around Moses Rock diatreme, a kimberlite-bearing dike in SW Utah, was examined using internally calibrated Airborne Imaging Spectrometer (AIS) data. Distinct near-infrared absorption characteristics of clays, gypsum, and serpentine (a key marker for kinberlite concentration) allowed the surface units containing these components to be identified spatially and the relative abundance of each component measured. Within the dike itself, channels and dispersed components of kimberlite and blocks of country rocks were accurately determined.

Description: Analysis of Airborne Imaging Spectrometer (AIS) data acquired in Australia has revealed a number of operational problems. Horizontal striping in AIS imagery and spectral distortions due to order overlap were investigated. Horizontal striping, caused by grating position errors can be removed with little or no effect on spectral details. Order overlap remains a problem that seriously compromises identification of subtle mineral absorption features within AIS spectra. A spectrometric model of the AIS was developed to assist in identifying spurious spectral features, and will be used in efforts to restore the spectral integrity of the data.

Description: The Airborne Imaging Spectrometer (AIS) samples a region which is strongly influenced by decreasing solar irradiance at longer wavelengths and strong atmospheric absorptions. Four techniques, the Log Residual, the Least Upper Bound Residual, the Flat Field Correction and calibration using field reflectance measurements were investigated as a means for removing these two features. Of the four techniques field reflectance calibration proved to be superior in terms of noise and normalization. Of the other three techniques, the Log Residual was superior when applied to areas which did not contain one dominant cover type. In heavily vegetated areas, the Log Residual proved to be ineffective. After removing anomalously bright data values, the Least Upper Bound Residual proved to be almost as effective as the Log Residual in sparsely vegetated areas and much more effective in heavily vegetated areas. Of all the techniques, the Flat Field Correction was the noisest.

Description: Spectral characteristics of semi-arid shrub communities were examined using Airborne Imaging Spectrometer (AIS) data collected in the tree mode on 23 May 1985. Mesic sites with relatively high vegetation density and distinct zonation patterns exhibited greater spectral signature variations than sites with more xeric shrub communities. Spectral signature patterns were not directly related to vegetation density or physiognomy, although spatial maps derived from an 8-channel maximum likelihood classification were supported by photo-interpreted surface features. In AIS data, the principal detected effect of shrub vegetation on the alluvial fans is to lower reflectance across the spectrum. These results are similar to those reported during a period of minimal physiological activity in autumn, indicating that shadows cast by vegetation canopies are an important element of soil-vegetation interaction under conditions of relatively low canopy cover.

Description: Airborne Imaging Spectrometer (AIS) data were acquired for several vegetation types within the humid temperate eastern United States. The spectral region covered, 0.9 to 2.1 microns, was little used in vegetation studies. A preliminary analysis of spectral curves suggests that variations between vegetation spectra may be useful for discriminating plant communities. Calibration and normalization procedures must be refined to compensate for cloud cover, detector and other system noise, and possible second-order effects.

Description: Spectral reflectance properties of deciduous oak-hickory forests covering the eastern half of the Rolla Quadrangle were examined using Thematic Mapper (TM) data acquired in August and December, 1982 and Airborne Imaging Spectrometer (AIS) data acquired in August, 1985. For the TM data distinctly high relative reflectance values (greater than 0.3) in the near infrared (Band 4, 0.73 to 0.94 micrometers) correspond to regions characterized by xeric (dry) forests that overlie soils with low water retention capacities. These soils are derived primarily from rhyolites. More mesic forests characterized by lower TM band 4 relative reflectances are associated with soils of higher retention capacities derived predominately from non-cherty carbonates. The major factors affecting canopy reflectance appear to be the leaf area index (LAI) and leaf optical properties. The Suits canopy reflectance model predicts the relative reflectance values for the xeric canopies. The mesic canopy reflectance is less well matched and incorporation of canopy shadowing caused by the irregular nature of the mesic canopy may be necessary. Preliminary examination of high spectral resolution AIS data acquired in August of 1985 reveals no more information than found in the broad band TM data.

Description: Techniques using Munsell color transformations were developed for reducing 128 channels (or less) of Airborne Imaging Spectrometer (AIS) data to a single color-composite-image suitable for both visual interpretation and digital analysis. Using AIS data acquired in 1984 and 1985, limestone and dolomite roof pendants and sericite-illite and other clay minerals related to alteration were mapped in a quartz monzonite stock in the northern Grapevine Mountains of California and Nevada. Field studies and laboratory spectral measurements verify the mineralogical distributions mapped from the AIS data.

Description: Airborne Imaging Spectrometer (AIS) data, field and laboratory spectra and samples for X-ray diffraction analysis were collected in argillically altered Tertiary volcanic rocks in the Hot Creek Range, Nevada. From laboratory and field spectral measurements in the 2.0 to 2.4 micron range and using a spectroradiometer with a 4 nm sampling interval, the absorption band centers for kaolinite were loacted at 2.172 and 2.215 microns, for montmorillonite at 2.214 micron and for illite at 2.205. Based on these values and the criteria for resolution and separtion of spectral features, a spectral sampling interval of less than 4 nm is necessary to separate the clays. With an AIS spectral sampling interval of 9.3 nm, a spectral matching algorithm is more effective for separating kaolinite, montmorillonite, ad illite in Hot Creek Range than using the location of absorption minima alone.

Description: Airborne Imaging Spectrometer (AIS) data were collected over Virginia City, Nevada; an area of gold and silver mineralization with extensive surface exposures of altered volcanic rocks. The data were corrected for atmospheric effects by a flat-field method, and compared to library spectra of various alteration minerals using a spectral analysis program SPAM. Areas of strong clay alteration were identified on the AIS images that were mapped as kaolinitic, illitic, and sericitic alterations zones. Kaolinitic alteration is distinguishable in the 2.1 to 2.4 and 1.2 to 1.5 micrometer wavelength regions. Montmorillonite, illite, and sericite have absorption features similar to each other at 2.2 micrometer wavelength. Montnorillonite and illite also may be present in varying proportions within one Ground Instantaneous Field of View (GIFOV). In general AIS data is useful in identifying alteration zones that are associated with or lie above precious metal mineralization at Virginia City.

Description: Airborne Imaging Spectrometers (AIS) data collected in 1984 and 1985 showed pronounced striping in the vertical and horizontal directions. This striping reduced the signal to noise ratio so that features of the spectra of forest canopies were obscured or altered by noise. This noise was removed by application of a notch filter to the Fourier transform of the imagery in each waveband.

Description: Selective absorption of electromagnetic radiation by atmospheric gases and water vapor is an accepted fact in terrestrial remote sensing. Until recently, only a general knowledge of atmospheric effects was required for analysis of remote sensing data; however, with the advent of high spectral resolution imaging devices, detailed knowledge of atmospheric absorption bands has become increasingly important for accurate analysis. Detailed study of high spectral resolution aircraft data at the U.S. Geological Survey has disclosed narrow absorption features centered at approximately 2.17 and 2.20 micrometers not caused by surface mineralogy. Published atmospheric transmission spectra and atmospheric spectra derived using the LOWTRAN-5 computer model indicate that these absorption features are probably water vapor. Spectral modeling indicates that the effects of atmospheric absorption in this region are most pronounced in spectrally flat materials with only weak absorption bands. Without correction and detailed knowledge of the atmospheric effects, accurate mapping of surface mineralogy (particularly at low mineral concentrations) is not possible.

Description: Several laboratory calibration tests were developed for the Airborne Imaging Spectrometer (AIS). The goals of these tests are to adjust the physical alignment of the detector within the optical system and set the spectral endpoints, and produce a calibration file of multipliers which equalizes the relative responses of each of the detector elements in the entire two-dimensional array. Tests are also performed as part of an ongoing effort to provide absolute radiometric calibration. The tests are described and the merits and limitations of each are discussed.

Description: The first field test of NASA's Global Positioning System (GPS) Geodetic Program took place in March of 1985. The principal objective of this test was the demonstration of the feasibility of the fiducial station approach to precise GPS-based geodesy and orbit determination. Other objectives included an assessment of the performance of the several GPS receiver types involved in these field tests and the testing of the GIPSY software for GPS data analysis. In this article, the GIPSY (GPS Inferred Positioning System) software system is described and baseline solutions are examined for consistency with independent measurements made using very long baseline interferometry.

Description: With the advent of frequent Space Transportation System Shuttle missions, photography from hyperaltitudes stands to become an accessible and convenient resource for scientists and environmental managers. As satellite products (such as LANDSAT) continue to spiral in costs, all but the most affluent consumer is finding Earth imagery from space to be more and more unavailable. Therefore, the potential for Shuttle photography to serve a wide variety of users is increasing. However, despite the popularity of photos from space as public relations tools and report illustrations, little work has been performed to prove their scientific worth beyond that as basic mapping bases. It is the hypothesis of this project that hand-held Earth photography from the Space Shuttle has potentially high scientific merit and that primary data can be extracted. In effect, Shuttle photography should be considered a major remote sensing information resource.

Description: Imagery collected on July 11, 1981 from the Advanced Very High Resolution Radiometer aboard the NOAA-7 spacecraft was used in a four-channel (channels 1 to 4) classification study for forest, agriculture/grass, and urban categories. The class signatures composing these categories were compared using the transformed divergence algorithm. Separability in all instances was found to be dominated by emitted radiation more so by channel 3 (3.55 to 3.93 microns) than by channel 4 (10.5 to 11.3 microns). Laboratory spectra obtained for the 3.55 to 3.93-micron region showed that for leaves the transmission was virtually zero, and the reflectances on the leaves and soil investigated were about three percent. Thus, emitted radiation dominated reflected radiation as the mechanism responsible for class separability in this spectral region. The enhancement in the separability contributed by channel 3 over that of channel 4 resulted primarily from the temperature dependence of the Planck function, and to a lesser extent by the increased transmission within channel 3 relative to channel 4.

Description: The weighted-shift-and-add speckle imaging technique is analyzed using simple assumptions. The end product is shown to be a convolution of the object with a typical point-spread function (psf) that is similar in shape to the telescope psf and depends marginally on the speckle psf. A filter can be applied to each data frame before locating the maxima, either to identify the speckle locations (matched filter) or to estimate the instantaneous atmospheric psf (Wiener filter). Preliminary results show the power of the technique when applied to photon-limited data and to extended objects.

Description: A general theory based on the implicit mathematical determinacy, and a corresponding algorithm, are developed to derive topographic maps from radar images as photometric arrays. Starting from a control profile, the theory produces topography by an area integration of radar brightness, and the control profile is formed under the assumption that the terrain properties are locally cylindrical. The calibration curve for pixel brightness versus incidence-angle is also produced. In the operational algorithm, topography is produced as a set of independent line integrations down each of the parallel range lines of the image using the theory for control-profile formation. An adaptive technique was employed to process SEASAT images of sand dunes, and the present method is demonstrated with a Motorola image of Crazy Jug Point in the Grand Canyon.

Description: A liquid-nitrogen cooled, multidetector Fourier transform spectrometer has been constructed to measure minor stratospheric constituents via high resolution, earth-limb emission spectroscopy from a balloon-borne platform. Cryogenic cooling, combined with the use of extrinsic silicon photoconductor detectors cooled to liquid-helium temperature, allows the detection of weak emission features of gaseous species. The spectrometer has two basic scan modes: the first mode records the continuous spectrum from 650-2100/cm with 0.2/cm resolution; the second simultaneously records four preselected narrow intervals (about 175/cm bandpass each) with 0.02/cm resolution, unapodized. Filtering of the interferogram signal is done by real-time, digital signal processing. The most important feature of this flat mirror Michelson system, with respect to remote balloon-borne operation, is the dynamic alignment system which maintains the relative parallelism of the two flat reflectors of the interferometer. Species identified to date in data obtained during a Nov. 6, 1984, flight include: CO2, O3, H2O, CH4, HNO3, N2O, NO2, NO, CCl3F (Freon-11) and CF2Cl2 (Freon-12).

Description: Photoemission and SEXAFS experiments were conducted using a double crystal monochromator at the Stanford Synchrotron Radiation Laboratory. Photoelectrons were detected using a Surface Science Laboratories SSX-100 electron analyzer, which employs a magnetic/electrostatic lens, hemispherical geometry, and a two-dimensional position-sensitive detector. In the kinetic energy range of interest (1000-2000 eV), a significant improvement in count rate was observed over a single channel cylindrical mirror analyzer system. Ten second scans of the KLL silicon Auger peak manifold were recorded at a large number of photon energies for subsequent determination of SEXAFS spectra.

Description: The use of remote sensing to discriminate, measure, and map forest damage is evaluated. TM spectal coverage, a helicopter-mounted radiometer, and ground-based surveys were utilized to examine the responses of the spruces and firs of Camels Hump Mountain, Vermont to stresses, such as pollution and trace metals. The basic spectral properties of vegetation are described. Forest damage at the site was estimated as 11.8-76.0 percent for the spruces and 19-43.8 percent for the balsam firs. Shifts in the spectra of the conifers in particular in the near IR region are analyzed, and variations in the mesophyll cell anatomy and pigment content of the spruces and firs are investigated. The relations between canopy moisture and damage is studied. The TM data are compared to aircraft data and found to be well correlated.

Description: Results of laboratory experiments with a standard multiwire imaging proportional counter (MWPC), modified to include a parallel grid preamplification stage are presented. Both argon and xenon were used as the primary absorbing gas in conjunction with a number of quench gases. It is found that extremely good energy resolution is obtained from the preamplification stage, almost independent of the ionization potential of the quench gas and over a broad range of gains. Furthermore, regardless of absorbing gas or quench agent, there was no difficulty in transferring a portion of this preamplified charge to the MWPC section for multistep mode operation. Finally, even for overall system gains greater than 10,000, the energy resolution from the second stage is found to be significantly improved, as long as the preamplification stage is operating. These results should have wide application and are of special interest for X-ray astronomy.

Description: Conventional enhancements for the color display of multispectral images are based on independent contrast modifications or 'stretches' of three input images. This approach is not effective if the image channels are highly correlated or if the image histograms are strongly bimodal or more complex. Any of several procedures that tend to 'stretch' color saturation while leaving hue unchanged may better utilize the full range of colors for the display of image information. Two conceptually different enhancements are discussed: the 'decorrelation stretch', based on principal-component (PC) analysis, and the 'stretch' of 'hue' - 'saturation' - intensity (HSI) transformed data. The PC transformation in scene-dependent, but the HSI transformation is invariant. Examples of images enhanced by conventional linear stretches, decorrelation stretch, and by stretches of HSI transformed data are compared. Schematic variation diagrams or two- and three-dimensional histograms are used to illustrate the 'decorrelation stretch' method and the effect of the different enhancements.

Description: The design and performance of a small belt-type skin-friction gage to measure wall shear-stress coefficients in wind-tunnel testing are described, summarizing the report of Vakili and Wu (1982). The sensor employs a flexible belt of variable surface characteristics; this belt, wrapped tightly around two cylinders mounted on frictionless flexures, is equipped with strain gages to estimate the deflection of the belt by the flow. An alternative approach uses IR illumination, optical fibers, and a photosensitive transistor, permitting direct measurement of the belt deflection. Drawings, diagrams, and graphs of sample data are provided.

Description: This paper describes techniques that have been developed at JPL for visualization and measurements of droplet fields in a moving airstream. The techniques have been applied to a variety of problems which include simulation of heavy rain conditions in a wind tunnel, engine ingestion of wheel spray, analysis of fuel nozzle sprays and aerodynamic breakup of non-Newtonian liquids. The approach pursued here is direct imaging using a pulsed laser illumination source, followed by digital processing of photographic images. A laser double pulse technique has been used for determination of droplet velocities. Laser induced fluorescence has been used to enhance droplet definition in photographic images. The image processing software developed is capable of distinguishing between out-of-focus and in-focus drops, retaining only the latter for size determination.

Description: The relation between the normalized difference vegetation index (NDVI) and the herbaceous vegetation in Tamasane, Shakwe, and Masama in eastern Botswana is studied using 1983-1984 AVHRR data. The procedures for Landsat MSS interpolation of ground measurements and the data processing of the AVHRR data are described. The temporal sequence AVHRR global-area coverage (GAC) composite NDVI is examined. The AVHRR GAC composite NDVI and biomass and Landsat MSS interpolations of field measurements are analyzed and compared.

Description: Normalized difference vegetation index data obtained from polar-orbiting meteorological satellites were used to compare the growing or rainy seasons of 1984 and 1985 for the Sahelian zone of Africa. A substantial difference was found between these two years, with 1985 generally having higher normalized difference vegetation index values indicating higher levels of primary production in 1985 than in 1984. 1 km data were compared for Senegal, Mali, Niger and Sudan, and 7 km data were compared for sub-Saharan Africa. The qualitative comparison of these data suggests the use of similar data to assist in centralized monitoring of rangeland conditions, to identify areas of deficiencies in primary production and provide synoptic information in support of regional drought monitoring.

Description: Red and near-infrared satellite data from the Advanced Very High Resolution Radiometer sensor have been processed over several days and combined to produce spatially continuous cloud-free imagery over large areas with sufficient temporal resolution to study green-vegetation dynamics. The technique minimizes cloud contamination, reduces directional reflectance and off-nadir viewing effects, minimizes sun-angle and shadow effects, and minimizes aerosol and water-vapor effects. The improvement is highly dependent on the state of the atmosphere, surface-cover type, and the viewing and illumination geometry of the sun, target and sensor. An example from southern Africa showed an increase of 40 percent from individual image values tothe final composite image. Limitations associated with the technique are discussed, and recommendations are given to improve this approach.

Description: Leaf structure and function are shown to result in distinctive variations in the absorption and reflection of solar radiation from plant canopies. The leaf properties that determine the radiation-interception characteristics of plant canopies are directly linked to photosynthesis, stomatal resistance and evapotranspiration and can be inferred from measurements of reflected solar energy. The effects of off-nadir viewing and atmospheric constituents, coupled with the need to measure changing surface conditions, emphasize the need for multitemporal measurements of reflected radiation if primary production is to be estimated.

Description: A versatile multifunction package, POLYSITE, developed for Goddard's Land Analysis System, is described which simplifies the process of interactively selecting and correcting the sites used to study Landsat TM and MSS images. Image switching between the zoomed and nonzoomed image, color and shape cursor change and location display, and bit plane erase or color change, are global functions which are active at all times. Local functions possibly include manipulation of intensive study areas, new site definition, mensuration, and new image copying. The program is illustrated with the example of a full TM maser scene of metropolitan Washington, DC.

Description: The degree to which the GOES-VISSR infrared data can be used to infer area-averaged soil moisture is explored for a five-day case study period. Chosen variables are transformed and incorporated into a multiple linear regression. The actual observations, rather than a simplified model, are used to determine the relationship between soil moisture and GOES-IR radiance. It is shown that a depletion coefficient of 0.92 produces an index of ground truth which is best correlated with soil moisture as inferred from GOES thermal infrared data. When all individual daily soil estimates during the case study period are averaged at each point and compared to the average observed soil moisture, the data correlate at 0.85. This implies that the algorithm can distinguish at least four categories of soil moisture.

Description: The projections of leaf areas onto a horizontal plane and onto a vertical plane are examined for their utility in characterizing canopies for sunlight penetration (direct beam only) models. These projections exactly specify the penetration if the projections on the principal plane of the normals to the top surfaces of the leaves are in the same quadrant as the sun. Inferring the total leaf area from these projections (and therefore the penetration as a function of the total leaf area) is possible only with a large uncertainty (up to + or - 32 percent) because the projections are a specific measure of the total leaf area only if the leaf angle distribution is known. It is expected that this uncertainty could be reduced to more acceptable levels by making an approximate assessment of whether the zenith angle distribution is that of an extremophile canopy.

Description: Simultaneous co-located observations from two different orbits lead to several advantages (i.e., cross calibration of sensors and a wider range of solar-zenith and sensor look angles). The question was asked how many times per year (on the average) do the sub-satellite points of two satellites simultaneously come within D kilometers of each other? For the Space Station (altitude: 500 km, inclination: 28 deg) and a Sun synchronous satellite (altitude 705 km, inclination 98.21 deg) the answers are 16, 41 and 82 times per year for encounter distances D of 20, 50, and 100 km respectively. The relationship between encounters per year and distance D is linear. The answers were obtained in two ways: (1) a closed form statistical approach which led to a simple algebraic expression, and (2) a Monte Carlo type computer solution. The largest difference between the two solutions was less than 12 percent.

Description: The technology and applications of terrestrial remote sensing (RS) are discussed in reviews and reports. Topics examined include the future of the NASA earth-sciences program, NOAA plans for earth observations in the 1990s, space RS in France, international coordination of RS satellite programs, and applications of geocoded imagery. Consideration is given to spatial and tabular databases for order-three soil surveys, an AVHRR and Landsat regional inventory of irrigated agriculture, classification of wetlands, microwave radiometry of ocean surface winds and sea ice, and floodplain land-cover mapping with Thematic-Mapper data.

Description: The purpose of ISLSCP is to verify the use of satellite data for the estimation of land-surface properties. This is to be done through a series of field experiments using a combination of point measurements on the ground and areal measurements from aircraft overflights. In addition to validating satellite estimates of surface properties, approaches for obtaining areal averages of the radiation, moisture, and heat fluxes from remotely sensed data are to be studied. The procedure for doing this is to combine the surface point measurements of the fluxes with the aircraft areal observations using a surface-energy-balance model. This should make it possible to interpolate between the point estimates of these fluxes and calculate area-averaged quantities. The surface parameters to be estimated from aircraft observations include: surface radiation temperature, albedo, land-cover or vegetation index, and surface soil moisture.

Description: This paper presents preliminary results of C-band radar scatterometer measurements of forest canopies of southeastern forests in the vicinity of NASA/NSTL. The results are as follows: radar backscattering coefficients (BSCs) of deciduous forests are higher than those of coniferous forests at a large incidence angle by ranging measurement, the VV polarization BSCs obtain peak value at the first few meters from the canopy top and decrease rather quickly, while the HH polarization BSCs obtain peak value at longer distances from the canopy top and decrease rather slowly through the canopy; and tree canopies with higher attenuations have higher BSCs for all three polarizations, with VV polarization containing the largest differential (2.2 dB).

Description: A new gas-correlation spectroscopy technique is described which uses electrooptic phase modulation (EOPM) of atmospheric emission spectra together with a reference cell to selectively detect radiatively active gases. Laboratory results demonstrate that the EOPM gas-correlation technique is a sensitive approach to species abundance measurements, and support the feasibility of an instrument for measurement of winds in the stratosphere and mesosphere using an EOPM. Through the measurement of wind-induced Doppler shifts in the spectra of atmospheric species, this instrument offers a means of monitoring the wind field in the 20-100 km altitude range from a satellite.

Description: An overview of several multivariate image processing techniques is presented, with emphasis on techniques based upon the principal component transformation (PCT). Multiimages in various formats have a multivariate pixel value, associated with each pixel location, which has been scaled and quantized into a gray level vector, and the bivariate of the extent to which two images are correlated. The PCT of a multiimage decorrelates the multiimage to reduce its dimensionality and reveal its intercomponent dependencies if some off-diagonal elements are not small, and for the purposes of display the principal component images must be postprocessed into multiimage format. The principal component analysis of a multiimage is a statistical analysis based upon the PCT whose primary application is to determine the intrinsic component dimensionality of the multiimage. Computational considerations are also discussed.

Description: Airborne-SAR, SIR-A, Seasat SAR, and Landsat TM images of the Savannah River Plant, a gently sloping area of South Carolina covered with diverse vegetation, are presented and briefly characterized. Preliminary results indicate that multiple-polarization images constructed from the airborne-SAR data give some indication of forest density and understory growth but do not permit discrimination between evergreen and deciduous forests. Heat-tolerant vegetation growing on sand bars in streams bearing thermal effluents from nuclear reactors on the site is found to have a distinguishing polarization signature.

Description: Images of forested low-relief terrain in the Amazon basin of Brazil, obtained with airborne imaging radar in the Radambrasil project, are compared with SIR-A and Landsat MSS band-7 images to evaluate their usefulness in constructing geologic maps. Sample images are shown, and it is found that Radam images are more useful in distinguishing drainage patterns and mapping the region distribution of stream channels due to their relatively low depression angles (less than 25 deg as opposed to 43-37 deg for SIR-A), but that SIR-A images give superior discrimination of alluvial forest, where trees stand in water, due to the higher reflectivity of branches and water at the SIR-A wavelength (23.5 cm as opposed to 3 cm for Radam). Alluvial forest is also identified by Landsat band 7.

Description: Forest canopies over different sedimentary lithologies of valleys and ridges are composed of different dominant species and have significantly different reflectance and emittance. In a botanical survey of eighty-seven forest sites, sedimentary lithologies were found to differ in the species which dominate the forest canopy. Sandstone sites had abundant chestnut oak (Quercus prinus), black oak (Q. velutina), and northern red oak (Q. rubra). On shale sites chestnut oak, white oak (Q. alba), northern red oak and red pine (Pinus resinosa) were dominant. Limestone sites had a variable species composition with the most common species, northern red oak, white oak, and black locust (Robinia pseudocacia) accounting for only 30 percent of the total trees. Thematic Mapper Simulator (TMS) data obtained during the growing season were analyzed to determine if sandstones, shales, and limestones could be distinguished on the basis of forest-canopy reflectance. The observations compared in the analysis were means of the eight TMS bands for 10 x 10-pixel test sites selected from areas with complete canopy closure. In August imagery the three lithologies were separable based on differences in TMS band 3 (630-690 nm) and band 8 (10.4-12.5 microns).

Description: The use of remote-sensing data on forest leaf flush to identify areas with anomalously high soil heavy-metal concentrations is demonstrated using airborne Thematic Mapper Simulator (TMS) leaf-area-index data obtained over two sites in Virginia in spring 1983 and 1984. Mean-reflectance differences, especially in the 760-900-nm and 630-690-nm bands, corresponding to delayed leaf flush are found to be good indicators of higher heavy-metal concentration. Airborne and ground-based canopy-temperature measurements are also shown to be significantly higher in high-heavy-metal areas than in control areas.

Description: This paper continues a study on the accuracy of geological mapping using Landsat Thematic Mapper data (Short, 1984). In June 1976, both the White Mountain alteration zone and the Waterpocket Fold sedimentary rock sites in Utah were surveyed by the Bendix 24-band scanner on a NASA NC-130B aircraft. Mid-June 1984 TM data for these two sites have been processed like the 1976 data to test the quality of simulation of TM data. Principal-components (PC) color composite images for White Mountain show close correspondence to the Bendix PC images. At this site carbonate strata are uniquely discriminated in both Bendix and TM composites that use an inverted PC 3 image. Alunite/kaolinite and hematite/limonite alteration zones developed on volcanic flows are also sharply separated, but iron oxide and silicified zones are less so. The accuracy of rock-units mapping at the Waterpocket Fold site by supervised classification of the June TM data is significantly better, reaching 70 percent in the best case, than for January 1983 data for that site.

Description: A geobotanical investigation based on the detection of premature leaf senescence was conducted in an area of predominantly chalcocite mineralization of the Keweenaw Peninsula in Michigan's Upper Peninsula. Spectrophotometric measurements indicated that the region from 600 to 700 nm captures the rise in red reflectance characteristic of senescent leaves. Observations at other wavelengths do not distinguish between senescent and green leaves as clearly and unequivocably as observations at these wavelengths. Small format black and white aerial photographs filtered for the red band (600 to 700 nm) and Thematic Mapper Simulator imagery were collected during the period of fall senescence in the study area. Soil samples were collected from two areas identified by leaf senescence and from two additional sites where the leaf canopy was still green. Geochemical analysis revealed that the sites characterized by premature leaf senescence had a significantly higher median soil copper concentration than the other two areas.

Description: Airborne Imaging Spectrometer (AIS) data were analyzed to deduce plant density and species composition in three semi-arid shrub-dominated communities of Owens Valley, CA, occurring on either a sand, granite alluvium, or basalt substrate. The high-spectral resolution AIS data were related to spectra obtained with field portable spectrometers, which in turn were related to plant and soil characteristics of the communities. Many of the dominant species have unique spectral features which permit their identification in AIS pixel images. The canopy-induced shadow may be a major factor influencing substrate spectral properties during fall and winter, because of low sun angles. Moreover, changes in spectral signatures following dormancy and leaf senescence tend to decrease contrasts between the plant community and the geologic substrate, also suggesting that fall and winter are a difficult time of year for spectral analyses.

Description: A preliminary interpretation of structure and lithology from selected Shuttle Imaging Radar-B (SIR-B) images of Borneo, collected in October 1984, is presented. The SIR-B images, obtained at depression angles that ranged from 40 to 50 deg, were interpreted by using the approaches suggested by Sabins (1983). On the basis of radar signatures, six terrain categories; coastal and alluvial plains, and carbonate, clastic, volcanic, and melange, rocks, were defined in east, central, and south Kalimantan, and in the Malaysian state of Sarawak.

Description: Landsat Thematic Mapper (TM) data collected in the late summer, fall, and winter of 1982 over forested bedrocks in southeastern Missouri were used in conjunction with forest surveys, field work, aerial photographs, and laboratory analyses to evaluate multispectral and seasonal information from visible and reflected IR data. The forested bedrock included granites, rhyolites, carbonates, and sandstones. High reflectance in band 4 (760-900 nm) in the summer scene corresponds to regions of xeric forest type. The fact that the xeric regions tend to develop flat-topped canopies, as opposed to irregular canopy surfaces of the wetter mesic areas, may partially control the TM response in bands 4, 5 (155-175 nm) and 7 (208-235 nm). The xeric regions correlated with soils having poor water retention capabilities, such as rhyolites and certain carbonate rocks with nonporous residum layers. An opposite relationship between xeric and mesic forest biomass was noted, if the commonly used TM band ratio 4/3 was used as a surrogate biomass measure. The high band 4 response over xeric forests gives anomalously high biomass estimates.

Description: State of the art applications of remote sensing in geological exploration programs are discussed along with research and development activities aimed at increasing the future capabilities of this technology for exploration geology. The topics considered include: technical issues in the state of the art; regional exploration models; remote sensing applications for hydrocarbon exploration; commercialization of remote sensing satellites; and data integration. Also addressed are: remote sensing applications for mineral exploration; geobotanical and environmental remote sensing; image processing techniques and applications; advanced sensors, radar, and airborne systems; and engineering, logistics, and marine applications.

Description: Multiple incidence angle SIR-B data of the Cordon la Grasa region of the Chubut Province of Argentina are used to discriminate various forest types by their relative brightness versus incidence angle signatures. The region consists of several species of Nothofagas which change in canopy structure with elevation, slope, and exposure. In general, the factors that appear to impact the radar response most are canopy structure, density, and ground cover (presence or absence of dead trunks and branches in particular). The results of this work indicate that (1) different forest species, and structures of a single species, may be discriminated using multiple incidence angle radar imagery and (2) it is essential to consider the variation in backscatter due to incidence angle when analyzing the comparing data collected at varying frequencies and polarizations.

Description: The images obtained by the Shuttle Imaging Radar (SIR)-A and -B systems over the southwestern Egypt and northwestern Sudan were coregistered with the Landsat images and the existing maps to aid in extrapolations of the buried paleodrainages ('radar rivers'), first discovered by SIR-A. Field observations explain the radar responses of three types of radar rivers, RR-1 (broad, aggraded valleys filled with alluvium), RR-2 (braided channels inset in the RR-1 valleys), and RR-3 (narrow, long, bedrock-incised channels). A generalized model of the radar rivers, based on field studies and regional geologic relations, shows inferred changes in river regimen since the large valleys were established during the later Paleogene-early Neogene. It is suggested that a former Trans-African master stream system may have flowed from headwaters in the Red Sea Hills southwestward across North Africa, discharging into the Atlantic at the Paleo-Niger delta, prior to the Neogene domal uplifts and building of volcanic edifices across the paths of these ancient watercourses.

Description: Synthetic Aperture Radar (SAR) images from the National Aeronautics and Space Administration's Shuttle Imaging Radar-B mission were used to analyze the effects of radar incidence angle on information content and vegetation penetration. Three SAR data sets using incidence angles of 26, 46, and 58 deg were acquired over the mangrove jungles of Southern Bangladesh. The data sets were digitally processed using 3 x 3, 7 x 7, and 11 x 11 spatial filters and geometrically registered to a multisource-multilevel-corraborative data base consisting of Landsat data, forest map data, and in situ acquired forest enumeration and topographic information. Analyses revealed that significant vegetation 'penetration' was found at all angles, and that tree and canopy structural morphology may exert an influence on this phenomenon.

Description: An experiment was conducted from an L-band SAR aboard Space Shuttle Challenger in October 1984 to study the microwave backscatter dependence on soil moisture, surface roughness, and vegetation cover. The results based on the analyses of an image obtained at 21-deg incidence angle show a positive correlatlion between scattering coefficient and soil moisture content, with a sensitivity comparable to that derived from the ground radar measurements reported by Ulaby et al. (1978). The surface roughness strongly affects the microwave backscatter. A factor of two change in the standard deviation of surface roughness height gives a corresponding change of about 8 dB in the scattering coefficient. The microwave backscatter also depends on the vegetation types. Under the dry soil conditions, the scattering coefficient is observed to change from about -24 dB for an alfalfa or lettuce field to about -17 dB for a mature corn field. These results suggest that observations with a SAR system of multiple frequencies and polarizations are required to unravel the effects of soil moisture, surface roughness, and vegetation cover.

Description: During the SIR-B mission in October 1984, a significant number of overlapping synthetic aperture radar (SAR) images of various ground areas was collected. This has offered the first opportunity to perform stereo analyses on images from space that cover large ground areas to determine elevation information. This paper presents the preliminary results of an investigation to obtain elevation data from stereo pairs of SIR-B images. First, the accuracy with which elevation information can be derived from SIR-B image pairs is evaluated theoretically. It is shown that elevation accuracy is a function of the slant range resolution, the incidence angles with which the stereo pair is obtained, the accuracies in spacecraft state estimation, and determination of corresponding pixels in the stereo pair. Next, a hierarchical method is developed to match the corresponding pixels. This method involves iterative removal of local distortions and correlations of pairs of local neighborhoods in the two images. Since it is necessary to perform the matching at every pixel in the image, it is very computationally intensive. Therefore, it has been implemented on the Massively Parallel Processor (MPP) at the Goddard Space Flight Center (GSFC). The MPP's speed permits two iterations of this technique to operate on a pair of 512 x 512 images within 7 s. Results of applying this algorithm of SIR-B images of Mount Shasta, CA, are shown. The matching algorithm performs well in regions of the image with significant features. An approximate elevation image derived from the matching process corresponds to published topographic map data, except for certain obvious discontinuities.

Description: On October 5, 1984, the second Shuttle Imaging Radar (SIR-B) was launched into orbit aboard the Space Shuttle Challenger. SIR-B is part of an evolutionary radar program designed to progressively develop a multifrequency, multipolarization synthetic aperture radar with a variable earth-imaging geometry. The SIR-B instrument is an upgraded version of SIR-A, with the additional capability of tilting the antenna mechanically to acquire imagery at variable incidence angles ranging from 15 to 60 deg. The variable look angle capability provided a means of acquiring multiple incidence angle imagery over specific targets on successive days of the mission. These data are being used to classify surface features by their backscatter signatures as a function of incidence angle and for topographic mapping. In addition to the antenna tilt capability, a digital data-handling system was added to increase the dynamic range, the resolution was improved by a factor of two over SIR-A, and a calibration subsystem was added to improve the radiometric accuracy of the data. The mission had a number of problems, including loss of the primary digital data path between the Shuttle and the ground. In spite of these problems, approximately 20 percent of the planned digital data were collected over the 8-day Shuttle mission corresponding to an areal coverage of about 6.4 million sq km.

Description: A research program is currently being conducted with the aim to investigate the operating environment of future gas turbines. The present paper provides a description of the experimental methods which have been employed in performing turbulence intensity measurements in shock-induced flows. In a discussion of the instrumentation, attention is given to the employed low pressure shock tube, the hot-wire probe, the anemometer, the test facility, the experimental setup, the Kistler pressure transducer, and silicon piezoresistive gages. Aspects of instrumentation calibration are considered along with data corrections, experimental data, and data processing.

Description: A stressed Ge:Ga infrared detector was tested in various operating conditions. Background-limited performance was demonstrated at photon backgrounds down to less than 10 to the 8th photon/s sq cm. The optimal operational parameters were determined.

Description: This article describes a separability measure for class discrimination. This measure is based on the Fisher information measure for estimating the mixing proportion of two classes. The Fisher information measure not only provides a means to assess quantitatively the information content in the features for separating classes, but also gives the lower bound for the variance of any unbiased estimate of the mixing proportion based on observations of the features. Unlike most commonly used separability measures, this measure is not dependent on the form of the probability distribution of the features and does not imply a specific estimation procedure. This is important because the probability distribution function that describes the data for a given class does not have simple analytic forms, such as a Gaussian. Results of applying this measure to compare the information content provided by three Landsat-derived feature vectors for the purpose of separating small grains from other crops are presented.

Description: The design of a low-energy ion facility for development and calibration of thermal ion instrumentation is examined. A directly heated cathode provides the electrons used to produce ions by impact ionization and an applied magnetic field increases the path length followed by the electrons. The electrostatic and variable geometry magnetic mirror configuration in the ion source is studied. The procedures for the charge neutralization of the beam and the configuration and function of the 1.4-m drift tube are analyzed. A microcomputer is utilized to control and monitor the beam energy and composition, and the mass- and angle-dependent response of the instrument under testing. The facility produces a high-quality ion beam with an adjustable range of energies up to 150 eV; the angular divergence and uniformity of the beam is obtained from two independent retarding potential analyzers. The procedures for calibrating the instrument being developed are described.

Description: The use of Suits' (1972a, b) digital radiative transfer model to simulate the effect of nonLambertian canopy reflectance on off-nadir observations of vegetation is discussed. Canopy reflectances of cord grass are calculated using the radiative transfer model, field radiometric measurements, and airborne multispectral scanner data. The effects of varying view angles on canopy reflectance are analyzed and compared. The comparison reveals that the model is effective in simulating the sense and magnitude of reflectance change due to variable angles of observations; however, the model does not reproduce the observed dependence of nadir canopy reflectance on solar zenith angle. It is concluded that the radiative transfer model is applicable for predicting the variation in canopy reflectance due to changing view zenith angles.

Description: For the study of human and animal vision, the video framebuffer is the only technology that is capable of displaying two-dimensional images with precise control of contrast, luminance, and display timing. The video framebuffer also allows precise control of color. However, this device is not designed for precise psychophysical displays, and techniques must be developed to use them in this role. In order to be concrete, an RDS-3000 raster display system (Adage, 1982) is used which is hosted by a PDP-11/73 under the Venix operating system. The principles generalize to other machines. Where it clarifies the issues, the syntax of the software routines involved is shown.

Description: The missions of the German Modular Optoelectronic Multispectral Scanner (MOMS) aboard two STS flights demonstrated the feasibility of a novel concept with regard to both technical and scientific objectives. On account of the successful missions, a cooperation was agreed between the German Federal Minister for Research nad Technology and NASA for comparing MOMS observations with the more familiar operational Landsat-TM data over selected test sites, as a means of obtaining some relative measure of performance. This paper summarizes the results obtained and presents the MOMS-02, a further experimental representative of the MOMS program aiming at the realization of an operational system for the mid-nineties.

Description: The analysis of a proposed new technique for capacitance type blade tip clearance measurement is presented. The capacitance between the blade tip and a mounted capacitance electrode within a guard ring forms one of the feedback elements of a high speed operational amplifier. The differential equation governing the operational amplifier circuit is formulated and solved for two types of inputs to the amplifier - a constant voltage and a ramp. The resultant solution shows an output that contains a term that is proportional to the derivative of the product of the input voltage and the time constant of the feedback network. The blade tip clearance capacitance is obtained by subtracting the output of a balancing reference channel followed by integration. The proposed sampled data algorithm corrects for environmental effects and varying rotor speeds on-line, making the system suitable for turbine instrumentation. System requirements, block diagrams, and a typical application are included.

Description: NASA Langley's Crash Response Data System (CRDS) which is designed to acquire aircraft structural and anthropomorphic dummy responses during the full-scale transport CID test is described. Included in the discussion are the system design approach, details on key instrumentation subsystems and operations, overall instrumentation crash performance, and data recovery results. Two autonomous high-environment digital flight instrumentation systems, DAS 1 and DAS 2, were employed to obtain research data from various strain gage, accelerometer, and tensiometric sensors installed in the B-720 test aircraft. The CRDS successfully acquired 343 out of 352 measurements of dynamic crash data.

Description: A miniature, computer-controlled, deadweight calibrator was developed to remotely calibrate a force transducer mounted in a cryogenic chamber. This simple mechanism allows automatic loading and unloading of deadweights placed onto a skin friction balance during calibrations. Equipment for the calibrator includes a specially designed set of five interlocking 200-milligram weights, a motorized lifting platform, and a controller box taking commands from a microcomputer on an IEEE interface. The computer is also used to record and reduce the calibration data and control other calibration parameters. The full-scale load for this device is 1,000 milligrams; however, the concept can be extended to accommodate other calibration ranges.

Description: An electronic scanner of pressure (ESOP) has been developed by NASA Ames Research Center for installation in wind tunnel models. An ESOP system consists of up to 20 pressure modules (PMs), each with 48 pressure transducers and a heater, an analog-to-digital (A/D) converter module, a microprocessor, a data controller, a monitor unit, a control and processing unit, and a heater controller. The PMs and the A/D converter module are sized to be installed in the models tested in the Ames Aerodynamics Division wind tunnels. A unique feature of the pressure module is the lack of moving parts such as a pneumatic switch used in other systems for in situ calibrations. This paper describes the ESOP system and the results of the initial testing of the system. The initial results indicate the system meets the original design goal of 0.15 percent accuracy.

Description: A multichannel design which makes use of the radiation normally rejected in a Fabry-Perot spectrometer is described, with application to infrared astronomy. The present optical design minimizes the diameters of the etalon and optics. The use of spherical mirrors ensures that no radiation is lost through the entrance aperture, and the beams can be completely collimated at the etalon. Laboratory studies demonstrate that the ability to employ eight channels increases by a factor of four the flux integrated during a given time period compared with that of a single-channel instrument. The spectrometer is nondispersive, and the source can be imaged at each of several output spectral positions.