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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

A stochastic analysis of terrain evaluation variables for path selection

A stochastic analysis was performed on the variables associated with the characteristics of the terrain encountered by a roving system with an autonomous navigation system. A laser rangefinder is employed to detect terrain features at ranges up to 75 m. Analytic expressions and a numerical scheme were developed to calculate the variance of data on these four variables: (1) body clearance, (2) in-path slope, (3) tilt slope, and (4) wheel deviation. The variance is due to noise in the range data. It was found that the standard deviation of these terrain variables is large enough to warrant the use of a safety margin to aid the roving vehicle in avoiding high risk areas.

Donohue, J. G.↗
NASA NTRS1980

A study of GEOS-3 terrain data with emphasis on radar cross section

Radar cross sections (RCS) of terrain are studied using GEOS 3 radar altimeter data. Maps of RCS for portions of four east coast states (U.S.A.) are presented and used to draw curves of RCS versus inland distance as measured from the land/sea interface. The results show RCS to decay approximately exponentially with inland distance. The GEOS 3 data are also used to develop curves of RCS seasonal variation for the same regions. Observed variations correlate strongly with local potential evaporation. Results also show that farming operations in the state of North Carolina are observable in the RCS data. A restricted method for determining surface roughness features from saturated average return waveforms for some types of terrain is developed. Sensor bias induced by receiver saturation for certain terrain returns is briefly discussed.

Priester, R. W.↗
NASA NTRS1980

Application of digital terrain data to quantify and reduce the topographic effect on LANDSAT data

Integration of LANDSAT multispectral scanner (MSS) data with 30 m U.S. Geological Survey (USGS) digital terrain data was undertaken to quantify and reduce the topographic effect on imagery of a forested mountain ridge test site in central Pennsylvania. High Sun angle imagery revealed variation of as much as 21 pixel values in data for slopes of different angles and aspects with uniform surface cover. Large topographic effects were apparent in MSS 4 and 5 was due to a combination of high absorption by the forest cover and the MSS quantization. Four methods for reducing the topographic effect were compared. Band ratioing of MSS 6/5 and MSS 7/5 did not eliminate the topographic effect because of the lack of variation in MSS 4 and 5 radiances. The three radiance models examined to reduce the topographic effect required integration of the digital terrain data. Two Lambertian models increased the variation in the LANDSAT radiances. The nonLambertian model considerably reduced (86 per cent) the topographic effect in the LANDSAT data. The study demonstrates that high quality digital terrain data, as provided by the USGS digital elevation model data, can be used to enhance the utility of multispectral satellite data.

Justice, C. O.↗
NASA NTRS1981

Terrain profiling from Seasat altimetry

To determine their applicability for terrain profiling, Seasat altimeter measurements were analyzed for the following geographic areas: (1) Andean salars of southern Bolivia; (2) Alaska; (3) south-central Arizona; (4) imperial Valley of California; (5) Yuma Valley of Arizona; and (6) Great Salt Lake Desert. Analysis of the data over all of these geographic areas shows that the satellite altimeter servo did not respond quickly enough to changing terrain features. However, it is demonstrated that retracking of the archived surface return waveforms yields surface elevations over smooth terrain accurate to + or - 1 m when correlated with large scale maps. The retracking algorithm used and its verification over the salars of southern Bolivia are described. Results are presented for each of the six geographic areas.

Brooks, R. L.↗
NASA NTRS1982

Analysis of geologic terrain models for determination of optimum SAR sensor configuration and optimum information extraction for exploration of global non-renewable resources. Pilot study: Arkansas Remote Sensing Laboratory, part 1, part 2, and part 3

Computer-generated radar simulations and mathematical geologic terrain models were used to establish the optimum radar sensor operating parameters for geologic research. An initial set of mathematical geologic terrain models was created for three basic landforms and families of simulated radar images were prepared from these models for numerous interacting sensor, platform, and terrain variables. The tradeoffs between the various sensor parameters and the quantity and quality of the extractable geologic data were investigated as well as the development of automated techniques of digital SAR image analysis. Initial work on a texture analysis of SEASAT SAR imagery is reported. Computer-generated radar simulations are shown for combinations of two geologic models and three SAR angles of incidence.

Kaupp, V. H.↗
NASA NTRS1983

Automated basin delineation from digital terrain data

While digital terrain grids are now in wide use, accurate delineation of drainage basins from these data is difficult to efficiently automate. A recursive order N solution to this problem is presented. The algorithm is fast because no point in the basin is checked more than once, and no points outside the basin are considered. Two applications for terrain analysis and one for remote sensing are given to illustrate the method, on a basin with high relief in the Sierra Nevada. This technique for automated basin delineation will enhance the utility of digital terrain analysis for hydrologic modeling and remote sensing.

Marks, D.↗
NASA NTRS1982

Estimating planetary terrain slopes from range measurements using a two dimensional spline smoothing technique

A new scanning scheme is presented for implementation for terrain slope estimation on a Martian exploratory rover. The rover will be equipped with a laser rangefinder as a principal sensing device for distance in its navigational equipment. A scan of the horizontal terrain from 5-50 m is indicated, and calculations are devised for quantifying the range errors. A constant incremental pointing angle is ruled out and a set of three pointing angles for different sub-areas of scan are defined. A two-dimensional smoothing algorithm is described for estimating slopes. The resultant scanning scheme involves the use of the characteristic curves derived from the relationships between the incremental elevation angle and the horizontal data spacing and the slope error index. A simulation was run and wavy terrain was produced from noise corrupted range measurements.

Kim, C. S.↗
NASA NTRS1983

Radar and infrared remote sensing of terrain, water resources, arctic sea ice, and agriculture

Radar range measurements, basic waveforms of radar systems, and radar displays are initially described. These are followed by backscatter from several types of terrain and vegetation as a function of frequency and grazing angle. Analytical models for this backscatter include the facet models of radar return, with range-angle, velocity-range, velocity-angle, range, velocity, and angular only discriminations. Several side-looking airborne radar geometries are presented. Radar images of Arctic sea ice, fresh water lake ice, cloud-covered terrain, and related areas are presented to identify applications of radar imagery. Volume scatter models are applied to radar imagery from alpine snowfields. Short pulse ice thickness radar for subsurface probes is discussed in fresh-water ice and sea ice detection. Infrared scanners, including multispectral, are described. Diffusion of cold water into a river, Arctic sea ice, power plant discharges, volcanic heat, and related areas are presented in thermal imagery. Multispectral radar and infrared imagery are discussed, with comparisons of photographic, infrared, and radar imagery of the same terrain or subjects.

Biggs, A. W.↗
NASA NTRS1984

Venus banded terrain - Tectonic models for band formation and their relationship to lithospheric thermal structure

Two classes of tectonic models for the formation of band structure on Venus mountain ranges are quantitatively evaluated: folding models and extensional models. The characteristics of banded terrain on Ishtar Terra are reviewed, particularly the evidence for a tectonic origin and such important details of band geometry as the spacing between adjacent bands. The tectonic models are tested against these observed features, and it it shown that both classes of models are possible explanations of banded terrain as long as the outer elastic-brittle layer of the Venus crust is at most a few kilometers thick. A general assessment is given of hypotheses for the origin of banded terrain and of the relationship between mechanical models for band formation and the thermal structure of the Venus lithosphere.

Solomon, S. C.↗
NASA NTRS1985

Formation of Bright Terrain Bands on Ganymede by Unstable Lithosphere Extension

The surface of Ganymede, as seen in Voyager images, was greatly modified by tectonic activity. Geologic evidence is consistent with the formation of younger bright terrain by the emplacement of icy material into rift zones formed in the older dark terrain. To better understand the formation of both terrestrial rift zones and bright terrain bands on Ganymede, the mechanics of rift initiation by the growth of necking instabilities in an extending lithosphere are studied. In particular, how an initial, small perturbation in lithosphere thickness at the lithosphere/asthenosphere boundary is amplified by uniform horizontal extension is studied. The lithosphere is treated as a layer of power-law viscous fluid of thickness H overlying a weaker, viscous mantle substrate. In order to assess the relative importance of buoyant upwelling and mechanical instability in rift formation, both density and strength stratification were incorporated into the model.

Zuber, M. T.↗
NASA NTRS1985

Origin of Martian Polygonal Terrain: Preliminary Results

The morphological characteristics of Martian polygonal terrain, and of the fractures defining the polygons were reviewed. The age relationships between the fractures defining the polygons and the material making up the polygonal terrain of Adamas Labyrinthus will be determined. This involves detailed mapping, with the relative ages of Key map units and the fractures determined by superposition and crater counts. The common occurrence of circular fracture patterns within the polygonal terrain is consistent with differential compaction over crater rims, and is easily accounted for by the tensile stresses that would be reasonably expected to occur in such places.

Mcgill, G. E.↗
NASA NTRS1985

Martian Fretted Terrain Morphometry Interpreted Using Principal Components Analysis

Martian fretted terrain is an extensive area of complex topography characterized by smooth, flat-floor valleys and mesas separated by abrupt escarpments along the boundary of heavily cratered uplands. The Deuteronilus-Protonilus region of the fretted terrain between latitude 35 degrees N and 50 degrees N and between 305 degrees W and 350 degrees W longitude was selected for quantitative landform study with the use of principal components analysis (PCA). The morphometry of upland mesa remnants and debris aprons was digitized with respect to latitude, longitude, and distance from the cratered terrain boundary (CTB). The PCA demonstrates that there are definable spatial variations in morphology with respect to longitude and latitude which suggest that the degradation along the CTB proceeded toward the southwest. The PCA also showed that there are organized relationships within the fretted landforms irrespective of their location. Finally, PCA indicated that an orientation of the degraded mesas exists which may be controlled by structure.

Kochell, R. C.↗
NASA NTRS1984

Electro-optical terrain reflectance modeling - A perspective

Electro-optical terrain reflectance modeling is one of the components required in the overall capability to simulate remote sensing measurement systems as an aid to the sensor or information processing designer. Given that sensor fields-of-view may vary from a few centimeters to several meters and that measurement devices may be placed at varying heights above the terrain surface, modeling of complex combinations of terrain classes or media with respect to both vertical and horizontal scales may be required. This paper addresses the issue of combining modeling approaches for different classes of materials in the optical regime and recommends a more formal approach to the radiative characterization of media properties as well as the calculation of the bidirectional reflectance distribution functions.

Smith, J. A.↗
NASA NTRS1989

Terrain-Following/Terrain-Avoidance System For Helicopters

Report describes early stages of development of control system enabling helicopter to follow automatically contours of terrain below and avoid collisions with terrain. Focuses on optimization of algorithm for generation of flightpath with respect to several variables, development of controller to position helicopter precisely along terrain-following/terrain-avoidance (TF/TA) flightpath, and integration of flightpath-trajectory software with flightpath-control software.

Dorr, Dan W.↗
NASA NTRS1988

Geophysical evidences for a thick crust south of Palghat-Tiruchi gap in the High Grade Terrains of South India

The regional gravity and magnetic features of the South Indian Shield were discussed. The prominent regional gravity low of 20 to 30 mgls over the charnockite terrain of South India, coupled with the correlation of a steep gravity gradient with a prominent shear zone to the north, can be interpreted in terms of increased crustal thickness in the South Indian high-grade terrain. There is some support for this from deep seismic sounding. The magnetic signature of the high-grade terrain is also distinctive, and Mishra argued that the Palghat-Tiruchi line might represent a Precambrian boundary such as a suture between two distinct crustal blocks.

Mishra, D. C.↗
NASA NTRS1990

Karst on Mars? The thumbprint terrain

The nature of the 'thumbprint' terrain noted by Guest et al. (1977) in high-resolution Viking Orbiter photographs of the northern plains of Mars is considered in light of plausible terrestrial analogs. At least some portion of such terrain may be due to differential solution of large carbonate deposits located in low-lying areas; comparative morphology may therefore indicate it to be an analog of the arid karst of Australia's Nullabor Plain, provided that groundwater flow was available during the terrain's formative period on Mars.

Schaefer, Martha W.↗
NASA NTRS1991

Matching Terrain-Height Maps For A Robotic Vehicle

Computational method for merging coarser- and finer-scale terrain-height data developed. Terrain-height data from aerial photographs merged with similar data on finer scale estimated from stereoscopic-vision and wheel-sensor outputs on robotic vehicle. Intended for use in guiding motions of proposed Mars rover vehicle, underlying concept applicable to such other problems as guiding semiautonomous robotic land vehicles in general and merging different topographical maps containing partly conflicting and/or partly unreliable data on same terrain.

Gennery, Donald B.↗
NASA NTRS1991

Perception, planning, and control for walking on rugged terrain

The CMU Planetary Rover project is developing a six-legged walking robot capable of autonomously navigating, exploring, and acquiring samples in rugged, unknown environments. To gain experience with the problems involved in walking on rugged terrain, a full-scale prototype leg was built and mounted on a carriage that rolls along overhead rails. Issues addressed in developing the software system to autonomously walk the leg through rugged terrain are described. In particular, the insights gained into perceiving and modeling rugged terrain, controlling the legged mechanism, interacting with the ground, choosing safe yet effective footfalls, and planning efficient leg moves through space are described.

Simmons, Reid↗