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  • LUNAR AND PLANETARY EXPLORATION  (7)
  • AIRCRAFT COMMUNICATIONS AND NAVIGATION  (3)
  • Canonical correspondence analysis  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 91 (1992), S. 338-345 
    ISSN: 1432-1939
    Keywords: River Great Ouse ; Canonical correspondence analysis ; Species-habitat interactions ; Stream restoration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Species-habitat relationships are an important aspect of fish life history, particularly in early ontogeny. To address the lack of information on the microhabitat use/requirements of European coarse fishes, particularly 0-group fishes in riverine systems, an empirical model was generated from data collected in the River Great Ouse catchment (UK). During 7 weeks in autumn 1990, data on young-of-the-year (0+) juvenile fishes and 15 environmental variables were collected at 2800 stratified, random point samples within 130 study sites (streams, rivers, side-channels, backwaters). Of 24 species of 0+ fish, only 10 were captured in ≥ 3% of non-null samples. Association analysis and canonical correspondence analysis of the samples-by-species (967×10) and samples-by-variables (967×15) data matrices revealed that the shallow, narrow, lotic, stony-pebbly channel microhabitat of riffles and runs was preferred by the progeny of substrate-spawning, substrate/plant-spawning and nest-guarding fishes. Moderately deeper and wider, sinuous channels, with slowto-moderate water velocities and medium-sized substrata were also favourable to progeny of substrate spawners. Assemblages of 0+ fish in deeper, wider, silted, trapezoidal-shaped channels with slow-to-lentic flowing water, i.e. channelised and regulated, were dominated by ubiquitous (plant/substrate) spawners.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5133
    Keywords: Microhabitat ; Typology ; Gabčíkovo hydroscheme ; Backwaters ; Point abundance sampling ; Canonical correspondence analysis ; Principal components analysis ; Anabranches
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis To address the lack of information on the distribution and habitat use of 0+ juvenile fishes in the Hungarian/Slovak flood plain of the middle Danube River, we undertook the first cross-border ichthyological investigation, examining three levels of ecological perception (hydrosystem, macrohabitat, microhabitat) during August 1992 using ‘Point Abundance Sampling’ by electrofishing. Being that the Gabćófcovo hydroscheme was about to begin diverting most of the river's discharge away from the flood plain during the winter of 1992, the present investigation represented the last chance to record the distribution and microhabitat use of 0+ fishes within the flood plain. At each sampling point, numerous environmental variables were measured quantitatively, or as percentages. At the hydrosystem level, 25 species of 0+ fishes were captured in the 1170 point samples collected from 52 sites (27 in Hungary, 25 in Slovakia), ranging from 10 to over 200 mm standard length (i.e. pikeEsox lucius). No significant differences were found between the Hungarian and Slovak specimens with respect to standard length (ANOVA, p〉 0.31), nor in the relative densities (ind.m−2) of 0+ fish (Student's t-test: df 24, t = 0.601, p = 0.553). A typology of macrohabitats using principal components analysis of the sites X species data matrix in absence/presence revealed three groupings of sites: (1) lotic channels, weirs and wing-dams; (2) partially-abandoned channels; (3) abandoned channels; the results corroborated our assumption that weirs of the anabranch systems represent a quasi-lotic refuge for rheophilous 0+ fishes of the flood plain during late summer. At the microhabitat level, an empirical model of microhabitat use was generated using canonical correspondence analysis and association analysis (based on chi-square probabilities). Water velocity was the most influential variable, with the O+ juveniles ordinated along the first canonical axis according to their increasing rheophily. The second most influential microhabitat variable was water transparency, followed by the percentage abundance of macrophytes and substrate composition.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2011-08-19
    Description: Magellan probes Venus'surface by 12.6-cm-wavelength vertical and oblique radar scattering and measures microwave thermal emission. Emissivity and root-mean-square slope maps between 330 deg and 30 deg E and 90 deg N and 80 deg S are dissimilar, although some local features are exceptions. Inferred surface emissivities typically are 0.85, but vary from 0.35 at Maxwell to 0.95 northeast of Gula Mons and other locations. Lowest emissivities appear in topographically high areas; this relation suggests that a phase change or differences in chemical weathering occur at about 6055-kilometer radius. Initial results indicate that there are significant variations in the surface scattering function.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 252; 265-270
    Format: text
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  • 4
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: The Magellan radar mapping mission is in the process of producing a global, high-resolution image and altimetry data set of Venus. Despite initial communications problems, few data gaps have occurred. Analysis of Magellan data is in the initial stages. The radar system data are of high quality, and the planned performance is being achieved in terms of spatial resolution and geometric and radiometric accuracy. Image performance exceeds expectations, and the image quality and mosaickability are extremely good. Future plans for the mission include obtaining gravity data, filling gaps in the initial map, and conducting special studies with the radar.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 252; 247-249
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  • 5
    Publication Date: 2019-01-25
    Description: The shape of seven large domes on the plains of Venus, with volumes between 100 and 1000 cu km, is compared with that of an axisymmetric gravity current spreading over a rigid horizontal surface. Both the altimetric profiles and the horizontal projection of the line of intersection of domes on the SAR images agree well with the theoretical similarity solution for a newtonian fluid, but not with the shape calculated for a rigid-plastic rheology, nor with that for a static model with a strong skin. As a viscous current spreads, it generates an isotropic strain rate tensor whose magnitude is independent of radius. Such a flow can account for the randomly oriented cracks that are uniformly distributed on the surface of the domes. The stress induced by the flow in the plains material below is obtained, and is probably large enough to produce the short radial cracks in the surface of the plains beyond the domes. The viscosity of the domes can be estimated from their thermal time constants if spreading is possible only when the fluid is hot, and lies between 10(exp 14) and 10(exp 17) Pa s. Laboratory experiments show that such viscosities correspond to temperatures of 610 - 690 C in dry rhyolitic magmas. These temperatures agree with laboratory measurements of the solidus temperature of wet rhyolite. These results show that the development of the domes can be understood using simple fluid dynamical ideas, and that the magmas involved can be produced by wet melting at depths below 10 km, followed by eruption and degassing.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 70
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  • 6
    Publication Date: 2019-06-28
    Description: A computer aiding concept for low-altitude helicopter flight was developed and evaluated in a real-time piloted simulation. The concept included an optimal control trajectory-generation algorithm based upon dynamic programming and a helmet-mounted display (HMD) presentation of a pathway-in-the-sky, a phantom aircraft, and flight-path vector/predictor guidance symbology. The trajectory-generation algorithm uses knowledge of the global mission requirements, a digital terrain map, aircraft performance capabilities, and advanced navigation information to determine a trajectory between mission way points that seeks valleys to minimize threat exposure. The pilot evaluation was conducted at NASA ARC moving base Vertical Motion Simulator (VMS) by pilots representing NASA, the U.S. Army, the Air Force, and the helicopter industry. The pilots manually tracked the trajectory generated by the algorithm utilizing the HMD symbology. The pilots were able to satisfactorily perform the tracking tasks while maintaining a high degree of awareness of the outside world.
    Keywords: AIRCRAFT COMMUNICATIONS AND NAVIGATION
    Type: NASA-TM-103883 , A-91219 , NAS 1.15:103883
    Format: application/pdf
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  • 7
    Publication Date: 2019-06-28
    Description: NASA and the U.S. Army have designed, developed, and flight evaluated a Computer Aiding for Low Altitude Helicopter Flight (CALAHF) guidance system. This system provides guidance to the pilot for near terrain covert helicopter operations. It automates the processing of precision navigation information, helicopter mission requirements, and terrain flight guidance. The automation is presented to the pilot through symbology on a helmet-mounted display. The symbology is a 'pilot-centered' design which preserves pilot flexibility and authority over the CALAHF system's automation. An extensive flight evaluation of the system has been conducted using the U.S. Army's NUH-60 STAR (Systems Testbed for Avionics Research) research helicopter. The evaluations were flown over a multiwaypoint helicopter mission in rugged mountainous terrain, at terrain clearance altitudes from 300 to 125 ft and airspeeds from 40 to 110 knots. The results of these evaluations showed that the pilots could precisely follow the automation symbology while maintaining a high degree of situational awareness.
    Keywords: AIRCRAFT COMMUNICATIONS AND NAVIGATION
    Type: NASA-TM-108837 , A-94112 , NAS 1.15:108837
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  • 8
    Publication Date: 2019-07-12
    Description: Radiothermal emission results obtained by the Magellan spacecraft during its first 8-month cycle of data taking, corresponding to one full rotation of Venus, are reported. The new Magellan data confirm the existence of regions with extremely low values of radiothermal emission. Possible mechanisms to explain the anomalous phenomena are an interaction with a single interface between the atmosphere and a high-dielectric permittivity medium versus volume scattering from the interior of a low-loss medium. The discrimination between these mechanisms requires careful observation of the polarized state of the radiothermal emission and that of the radar scattering.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8 A; 13
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  • 9
    Publication Date: 2019-07-12
    Description: During the first 8 months of the Magellan mission, the radar altimeter has made some three million measurements of the surface of Venus covering the latitude range from 85 deg N to 80 deg S. Methods involving range correlation, Doppler filtering, multiburst summation, and range migration are used to focus the observations and to achieve high surface resolution. Results are presented as maps of the global distribution of topography, meter-scale roughness, and power reflection coefficient. The results are similar to those reported in previous experiments (surface heights exhibit a unimodal distribution with more than 80 percent of the surface lying within 1 km of the 6051.84-km mean radius) but the higher resolution of the Magellan altimeter has disclosed several surprisingly steep features, e.g., the southwest face of the Maxwell Montes, the southern face of the Danu Montes, and the chasmata to the east of Thetis Regio, where average kilometer-scale slopes of greater than 30 deg are not uncommon. This conclusion is corroborated by close inspection of synthetic aperture radar imagery.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8 A; 13
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  • 10
    Publication Date: 2019-07-12
    Description: Pioneer Venus high-angle radar imaging data are used here to correct values of the specular power reflection coefficient for the effects of diffusely scattering small-scale surface roughness. A value of 5.0 + or - 0.9 is found for the average dielectric permittivity of the rolling plains and lowlands, suggesting that most of the Venus surface is overlain by at most only a few cm of soil or dust. The unexpectedly high values of power reflection coefficient are confirmed by observations of correspondingly low values of radiothermal emission. Thus there can be little doubt that most of the highlands contain significant amounts of a conducting mineral near the surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 14881-14
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