Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Surface Feature”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Analyses of Radar Images of Small Craters

Clouds hide the surface of Venus from all but radar imaging systems, supplemented by limited views from land spacecraft. Among the surfaces features likely to be observed by radar are craters that have formed by a variety of processes. In order to assess the radar characteristics of craters, volcanic craters and impact structures on Earth are described as imaged by the Shuttle Imaging Radar (SIR-A) experiment. Although most of the craters are small, this analysis provides insight into the ability to discriminate craters of various origins and provides some basis for interpreting radar images returned from Venus.

Greeley, R.↗
NASA NTRS1983

Analysis of Synthetic Aperture Radar data acquired over a variety of land cover

An analysis has been conducted of two-look-angle, multipolarization X-band SAR results. On the basis of the variety of land covers studied, the vertical-vertical polarization (VV) data is judged to contain the highest degree of contrast, while the horizontal-vertical (HV) polarization contained the least. VV polarization data is accordingly recommended for forest vegetation classification in those cases where only one data channel is available. The inclusion of horizontal-horizontal polarization data, however, is noted to be capable of delineating special surface features.

Wu, S. T.↗
NASA NTRS1985

The moons of Uranus, Neptune and Pluto

Voyager 2, launched in August 1977, will fly by Uranus in January, 1986, passing within 29,000 km of that planet's innermost moon, Miranda. It will subsequently encounter Neptune in August 1989, flying within 10,000 km of its inner satellite, Triton; images made of this moon by a high resolution camera are expected to reveal surface features as small as a few hundred meters in diameter. The composition of the Uranian moons will br inferred from their near-IR reflectance spectra and mean densities. While the spacecraft will not fly by Pluto, it is expected that the lessons learned from the Voyager encounters with Neptune and Uranus will expand current understanding of Pluto and its moon, Charon.

Brown, R. H.↗
NASA NTRS1985

Global and regional ridge patterns on Mars

A systematic study of Martian wrinkle ridges was performed to synthesize a theory of the planetary interior forces which produced such surface features. The survey was carried out using Mariner-9 and Viking orbiter imagery. Attention was given to the global distributions of ridge types in terms of geologic and tectonic surrounds, and to the orientation of ridges relative to impact basins. High/low relief ridges, ridge wings and rectilinear ridges were examined. Ridge orientation and distribution were found to be controlled by the forces of formation and modification of impact basins. Several other conclusions were reached regarding basin-concentric ridge patterns, regional stress patterns, regions of the most numerous ridges, and the location of a major compressive zone.

Chicarro, A. F.↗
NASA NTRS1985

Potential applications of multipolarization SAR for pine plantation biomass estimation

This study was conducted as a part of the research tasks under the Radar Land Cover Analysis Program. The Radar Land Cover Analysis objective is, through utilization of multisensor data, to gain a basic understanding of the measurements and data characteristics in the visible-IR-microwave regions of the electromagnetic spectrum associated with specific surface features and cover types. Since the results of analysis of data acquired by Shuttle Imaging Radar (SIR-A) and LANDSAT Thematic Mapper (TM) over the study area were reported (NSTL/ERL Report No. 228, December 1984), this study focused on the analysis and evaluation of the L-band multipolarization airborne SAR data acquired over a southeastern pine forest scene. The data acquisition mission was flown on September 8 and 9, 1983. The HH, HV polarizations and the VV, VH polarizations were used on the first and the second day, respectively. Due to instrumentation difficulties, the digital recorder recorded only the second day's data. Because of this, only the VV and VH polarization data were used in this analysis. However, the HH and HV polarization images were available for visual comparison. It appears that SAR digital numbers correlate with the index of green biomass.

Wu, S. T.↗
NASA NTRS1984

Vegetation and soils field research data base: Experiment summaries

Understanding of the relationships between the optical, spectral characteristics and important biological-physical parameters of earth-surface features can best be obtained by carefully controlled studies over fields and plots where complete data describing the condition of targets are attainable and where frequent, timely spectral measurement can be obtained. Development of a vegetation and soils field research data base was initiated in 1972 at Purdue University's Laboratory for Applications of Remote Sensing and expanded in the fall of 1974 by NASA as part of LACIE. Since then, over 250,000 truck-mounted and helicopter-borne spectrometer/multiband radiometer observations have been obtained of more than 50 soil series and 20 species of crops, grasses, and trees. These data are supplemented by an extensive set of biophysical and meteorological data acquired during each mission. The field research data form one of the most complete and best-documented data sets acquired for agricultural remote sensing research. Thus, they are well-suited to serve as a data base for research to: (1) quantiatively determine the relationships of spectral and biophysical characteristics of vegetation, (2) define future sensor systems, and (3) develop advanced data analysis techniques.

Biehl, L. L.↗
NASA NTRS1984

The importance and attainment of accurate absolute radiometric calibration

The importance of accurate absolute radiometric calibration is discussed by reference to the needs of those wishing to validate or use models describing the interaction of electromagnetic radiation with the atmosphere and earth surface features. The in-flight calibration methods used for the Landsat Thematic Mapper (TM) and the Systeme Probatoire d'Observation de la Terre, Haute Resolution visible (SPOT/HRV) systems are described and their limitations discussed. The questionable stability of in-flight absolute calibration methods suggests the use of a radiative transfer program to predict the apparent radiance, at the entrance pupil of the sensor, of a ground site of measured reflectance imaged through a well characterized atmosphere. The uncertainties of such a method are discussed.

Slater, P. N.↗
NASA NTRS1984

Topological grid structure - A data structure for earth science modeling

The automated analysis of land surface features is increasingly important to earth scientists. User-friendly algorithms for studying these features can be integrated into geographic information systems through the use of topological grid structure, which maintains the simplicity and transportability of standard grid structure while providing the essential capability to treat groups of contiguous, identically-classified pixels (corresponding to lakes, forests, fields, etc.) as distinct spatial entities.

Goldberg, M.↗
NASA NTRS1986

Field spectroscopy of agricultural crops

The development of the full potential of multispectral data acquired from satellites, requires quantitative knowledge, and physical models of the spectral properties of specific earth surface features. Knowledge of the relationships between spectral-radiometric characteristics and important biophysical parameters of agricultural crops and soils can best be obtained by carefully controlled studies of fields or plots. It is important to select plots where data describing the agronomic-biophysical properties of the crop canopies and soil background are attainable, taking into account also the feasibility of frequent timely calibrated spectral measurements. The term 'field spectroscopy' is employed for this research. The present paper is concerned with field research which was sponsored by NASA as part of the AgRISTARS Supporting Research Project. Attention is given to field research objectives, field research instrumentation, measurement procedures, spectral-temporal profile modeling, and the effects of cultural and environmental factors on crop reflectance.

Bauer, M. E.↗
NASA NTRS1986

The stratocumulus nature of fog

Landsat MSS and TM digital data on fog cell size distribution, cell aspect ratio, and cell orientation angle were analyzed for three high inversion radiation fogs in central California and on advection fog in eastern South Dakota. The results indicate that (1) fogs, being composed of individual cellular structures, are stratocumulus in nature; (2) the reflectance properties vary strongly across the cells, suggesting considerable variation in liquid water content; and (3) many fogs are patchy, often revealing surface features between the fog cells. The ratio of the wavelength between the fog cells and the height of the boundary layer was found to be between 2 and 3, and the typical horizontal aspect ratio of fog cells was about a factor of two. The observed quasi-periodic oscillations of measured fog variables may be caused by advection of the cellular structures across the observational site.

Welch, R. M.↗
NASA NTRS1986

SIR-B - The second Shuttle Imaging Radar experiment

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.

Cimino, J.↗
NASA NTRS1986

Photometry from Voyager 2 - Initial results from the Uranian atmosphere, satellites, and rings

The results of Voyager 2 photopolarimetry (PPS) surveys of Uranus, the ring system, occultation experiments and observations of the Uranian moons are reported. Dual-channel photometry and polarimetry data obtained of the atmosphere at various emission and phase angles are delineated and compared with characteristics of the Saturn and Jupiter atmospheres. The results of temperature, UV absorption and density profile calculations are also discussed. Extensive ring dimensional data, based on two occultation experiments, are provided in tabular form noting that the rings contain no dust. Finally, the geometric albedos of the five major moons and the phase curve of the moon Titania are presented. The latter data indicate that Titanian surface features are not the result of recent events such as volcanism or ice slurry outflows.

Lane, A. L.↗
NASA NTRS1986

Patterns of vegetation in the Owens Valley, California

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.

Ustin, S. L.↗
NASA NTRS1986

Observations of the seasonal variability of soil moisture and vegetation cover over Africa using satellite microwave radiometry

Multispectral passive microwave data from the scanning multichannel microwave radiometer (SMMR) on the Nimbus-7 satellite were processed selectively for a 1 yr period over Africa. The data show a wide dynamic range of brightness temperature (180 to 290 K), corresponding to variations in surface features such as moisture, temperature, vegetation, roughness, and large-scale topography. It appears that soil moisture variability is detectable with the SMMR over large regions of Africa. To what extent roughness and vegetation affect this capability is not clear. The lowest SMMR frequency is C-band (6.6 GHz), thus any soil moisture sensitivity at this frequency would be much improved by a sensor at L-band (1 to 2 GHz) less affected by roughness and vegetation.

Njoku, Eni G.↗
NASA NTRS1986

Geostationary microwave imagers detection criteria

Geostationary orbit is investigated as a vantage point from which to sense remotely the surface features of the planet and its atmosphere, with microwave sensors. The geometrical relationships associated with geostationary altitude are developed to produce an efficient search pattern for the detection of emitting media and metal objects. Power transfer equations are derived from the roots of first principles and explain the expected values of the signal-to-clutter ratios for the detection of aircraft, ships, and buoys and for the detection of natural features where they are manifested as cold and warm eddies. The transport of microwave power is described for modeled detection where the direction of power flow is explained by the Zeroth and Second Laws of Thermodynamics. Mathematical expressions are derived that elucidate the detectability of natural emitting media and metal objects. Signal-to-clutter ratio comparisons are drawn among detectable objects that show relative detectability with a thermodynamic sensor and with a short-pulse radar.

Stacey, J. M.↗
NASA NTRS1987

Voyager observations of 1985U1

Of the 10 small Uranian satellites, 1985U1 is the largest and the only one for which a resolved image was obtained by Voyager 2. In terms of albedo, the other nine satellites seem to be similar. Thus the single image of 1985U1 is important in suggesting what these other objects may be like. Size, shape, surface features, and photometry are examined.

Thomas, P.↗
NASA NTRS1987

Lunar and Planetary Science Conference, 17th, Houston, TX, Mar. 17-21, 1986, Proceedings. Part 2

The topics discussed in this volume include lunar endogenic rocks and processes; lunar regoliths and breccias; the terrestrial planets; shergottites; primitive materials, exposure, and atmospheres; and impacts and crater tectonics. Papers are presented on the petrology and geochemistry of alkali gabbronorites from lunar breccia 67975; the formation of Apollo 17 orange and black glass beads; mixing levels, the Apennine Front soil component, and compositional trends in the Apollo 15 soils; the meteorite component of Apollo 16 noritic impact melt breccias; and constraints on the lithospheric structure of Venus from mechanical models and tectonic surface features. Consideration is also given to a fractal interpretation of topography and geoid spectra on the earth, moon, Venus, and Mars; rare earth patterns in shergottite phosphates and residues; nuclide production by primary cosmic-ray protons; gas chromatographic instrumentation for the analysis of aerosols and gases in Titan's atmosphere; and finite-element models of non-Newtonian crater relaxation.

Ryder, Graham↗
NASA NTRS1987

Solar irradiance change and special longitudes due to r-modes

Sluggish global oscillations, having a periodicity of months and trapped in the sun's convection zone, modulate the amount of energy reaching earth and seem to impose some large-scale order on the distribution of solar surface features. These recently recognized oscillations (r-modes) increase the predictability of solar changes and may improve understanding of rotation and variability in other stars. Most of the 13 periodicities ranging from 13 to 85 days that are caused by r-modes can be detected in Nimbus 7 observations of solar irradiance during 3 years at solar maximum. These modes may also bear on the classical question of persistent longitudes of high solar activity.

Wolff, Charles L.↗