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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Variation of directional reflectance factors with structural changes of a developing alfalfa canopy

Directional reflectance factors of an alfalfa canopy were determined and related to canopy structure, agronomic variables, and irradiance conditions at four periods during a cutting cycle. Nadir and off-nadir reflectance factors decreased with increasing biomass in Thematic Mapper band 3(0.63-0.69 micrometer) and increased with increasing biomass in band 4(0.76-0.90 micrometer). The sensor view angle had less impact on perceived reflectance as the alfalfa progressed from an erectophile canopy of stems after harvest to a near planophile canopy of leaves at maturity. Studies of directional reflectance are needed for testing and upgrading vegetation canopy models and to aid in the complex interpretation problems presented by aircraft scanners and pointable satellites where illumination and viewing geometries may vary widely. Distinct changes in the patterns of radiance observed by a sensor as structural and biomass changes occur are keys to monitoring the growth and condition of crops.

Kirchner, J. A.↗
NASA NTRS1983

METCOR4: A program to simulate METSAT data

The METCOR4 program extracts radiation data from computer tapes and computes radiance as would be recorded by the NOAA6 and NOAA7 meteorological satellites (METSAT). Three different atmospheres, each with different aerosol concentration, are considered with the viewing geometry of the satellites and the expected solar geomtry. The FORTRAN program is provided.

Johnson, W. R.↗
NASA NTRS1983

High altitude Venus haze from Pioneer Venus limb scans

High-resolution limb scans of Venus made with the Orbiter Cloud Photopolarimeter aboard Pioneer Venus have been used to observe the high altitude Venus haze and its variation over almost one half a Venusian year. A model for a spherical atmosphere with tangential viewing geometry was used to analyze the observations and derive the haze properties. Values are found for the particle size and refractive index, particle number density and scale height, and eddy diffusion coefficient. Single scattering computations show good agreement with observed intensities for particles smaller than 0.3 micron radius and refractive index less than 1.7, consistent with, but not limited to, concentrated sulfuric acid. Particle scale height in the 0.5 to 2 mbar pressure regions varies between 1 and 3 km over the season, latitude, and local time ranges of the observations. Detached layers of haze are sometimes present. An average particle scale height of 2.2 km at 84 km altitude yields an eddy diffusion coefficient of 130,000 sq cm/sec.

Lane, W. A.↗
NASA NTRS1983

Saturn's pole - geometric correction based on voyager UVS and radio occultations

Measurements of of the opacity of Saturn's rings acquired during occultation experiments at radio (3.6 cm) and ultraviolet wavelengths were initially reduced to radial position rho using a standard pole vector. Common features in the two data sets from this reduction were offset by distances Delta rho(i). These offsets have been attributed to an error in the pole direction. Because the viewing geometries were quite different for the two experiments, the set of differences of Delta rho(i) provides a sensitive measure of corrections needed to refine the Saturn pole direction. The new standard pole vector in 1950.0 coordinates has right ascension alpha = 38.409 + or - 0.016 deg and declination delta = 83.324 + or - 0.002 deg.

Simpson, R. A.↗
NASA NTRS1984

Phobos: Close encounter imaging from the Viking Orbiters

The shape and orbital characteristics of Phobos, the larger and innermost of Mars' two irregular moons, are discussed and illustrated. Also presented are the high resolution pictures of Phobos that were obtained during the close flybys of Viking Orbiters 1 and 2. The viewing geometry is also given for each picture.

Duxbury, T. C.↗
NASA NTRS1983

Strength of mineral absorption features in the transmitted component of near-infrared reflected light - First results from RELAB

Bidirectional reflectance measurements are the only type of reflectance data available to the remote observer. For compositional interpretations, data are desired not only for identification of possible mineral components but also for modal abundance. The latter requires detailed information about the strength of absorption features. Using a new laboratory facility, the RELAB, laboratory data in the near infrared are presented that document effects of particle size, mineral mixtures, and viewing geometry for selected materials with well-developed absorption bands. The commonly observed increase in reflectance with decrease in particle size is also observed for absorption bands as well as a related decrease in absorption strength. For small particles in parts of the spectrum of maximum reflectance, however, a minor decrease in reflectance with a decrese in particle size is sometimes observed. Small particles dominate the observed characteristics of particulate surfaces, which contain a range of particle sizes. The mean optical path length (transmission through particles) of reflected radiation measured for a variety of particle sizes has an apparent upper limit of about 2 mm for particles of less than 250 microns. The typical number of particles involved in the optical path is less than 50.

Pieters, C. M.↗
NASA NTRS1984

Modeling crater topography and albedo from monoscopic Viking Orbiter images. I - Methodology

The methodology for a new photoclinometric technique for extracting topographic data from planetary images is described. The technique fully compensates for oblique viewing geometry prevalent in many spacecraft images. Brightness data are taken from a pair of profiles simultaneously, overcoming the problem of albedo variations in the application of photoclinometry to planetary surfaces. An additional procedure is described for eliminating the requirement of topographic symmetry along a pair of profiles. Test results show that both procedures have an accuracy of about two degrees for slopes of typical bowl-shaped craters, or about 5 percent for depths.

Davis, P. A.↗
NASA NTRS1985

Convergence of Chahine's nonlinear relaxation inversion method used for limb viewing remote sensing

The application of Chahine's (1970) inversion technique to remote sensing problems utilizing the limb viewing geometry is discussed. The problem considered here involves occultation-type measurements and limb radiance-type measurements from either spacecraft or balloon platforms. The kernel matrix of the inversion problem is either an upper or lower triangular matrix. It is demonstrated that the Chahine inversion technique always converges, provided the diagonal elements of the kernel matrix are nonzero.

Chu, W. P.↗
NASA NTRS1985

On stereo viewing of SAR images

Stereo viewing is indispensable for the measurement of homologue points in two overlapping images and the subsequent reconstruction of the three-dimensional topographic relief. Aspects of stereo viewing geometry are discussed along with problems of radar stereoscopy, taking into account stereo evaluation with an exaggeration factor, the viewability of real images, and radar stereoscopic computations. Attention is given to the definition of radar stereoscopic exaggeration, questions of image simulation, and the accuracy obtained with parallax measurements in radar images. An evaluation with a large set of about 40 radar stereo models demonstrates that same-side arrangements provide good stereo viewability. This result was confirmed for aircraft radar with look angles off-nadir of 60-80 deg and intersection angles between 0.2 deg and 23 deg, and for satellite radar (Seasat) with look angles of 20 deg and interaction angles of 1.2 deg - 4.8 deg.

Leberl, F. W.↗
NASA NTRS1986

High resolution remote sensing missions of a tethered satellite

The application of the Tethered Satellite (TS) as an operational remote sensing platform is studied. It represents a new platform capable of covering the altitudes between airplanes and free flying satellites, offering an adequate lifetime, high geometric and radiometric resolution and improved cartographic accuracy. Two operational remote sensing missions are proposed: one using two linear array systems for along track stereoscopic observation and one using a synthetic aperture radar combined with an interferometric technique. These missions are able to improve significantly the accuracy of future real time cartographic systems from space, also allowing, in the case of active microwave systems, the Earth's observation both in adverse weather and at any time, day or night. Furthermore, a simulation program is described in which, in order to examine carefully the potentiality of the TS as a new remote sensing platform, the orbital and attitude dynamics description of the TSS is integrated with the sensor viewing geometry, the Earth's ellipsoid, the atmospheric effects, the Sun illumination and the digital elevation model. A preliminary experiment has been proposed which consist of a metric camera to be deployed downwards during the second Shuttle demonstration flight.

Vetrella, S.↗
NASA NTRS1987

Photometric properties of lunar terrains derived from Hapke's equation

Hapke's bidirectional reflectance equations provide the most rigorous available description of photometric behavior in terms of physically meaningful parameters. The primary objective of this study was to derive Hapke parameters for the lunar surface from both disk-integrated and disk-resolved photometric data. Hapke's equation was fit to the disk-integrated phase curves and disk-resolved data for dark, average, and bright terrain classes using an iterative, nonlinear least squares algorithm described by Helfenstein. Parameters were initially determined from the disk-integrated data, and the result was applied as a first guess to the iterative solution of parameters for individual terrain classes. Plots are presented of the disk-resolved data normalized to corresponding brightnesses predicted from the disk-integrated solution under the same illumination and viewing geometries. Systematic trends in disk-resolved parameters can be identified. Values for single scattering albedo (w) of the dominantly anorthositic average and bright terrains are significantly larger than the value for the basaltic dark terrains (mare). Values for surge brightness parameters, particle phase function, and average topographic slope angle are also discussed.

Helfenstein, Paul↗
NASA NTRS1986

The vertical structure of limb hazes in the Martian atmosphere

Vertical distribution and reflectance properties of aerosols in the Martian atmosphere are presented, based on Viking Orbiter images containing the planetary limb. Profiles of scattered light above the limb are used to constrain the temporal and spatial behavior of the aerosols. The data cover a wide range of seasons, locations, and viewing geometries. The typical atmospheric column contains one or more discrete, optically thin, ice-like haze layers between 30 and 90 km elevation, depending on the season, whose composition is inferred to be water ice. Below the detached hazes there is a continuous haze extending to the surface. The continuous haze is rarely above 50 km and is much redder in color than the detached hazes above, implying a composition that has a strong dust component. The aerosol distribution exhibits solid seasonal control inferred to be driven by the variable solar flux around the orbit of Mars.

Jaquin, Fred↗
NASA NTRS1987

Observation of the O I ultraviolet intercombination emissions in the terrestrial dayglow

The first measurement of the 1173-A O I intercombination line in emission in the terrestrial dayglow was performed using the EUV-FUV spectrometer designed to be flown with the Astro-1 observatory. The atmospheric conditions and viewing geometry were such as to suppress nitrogen emission relative to those from atomic oxygen, permitting the identification and measurement of the weak O I 1173-A intercombination multiplet and the 1641-A line as well as the strong 989-A and 1304-A emissions. At lower altitudes, the 1173-A emission rate increased while the 989-A emission, from the same upper level, decreased. This behavior is consistent with the radiative entrapment model of Meier (1982) and the laboratory value of the 1173-A/989-A branching ratio measured by Morrison (1985). The 1641-A/1304-A emission ratio is also consistent with a radiative entrapment model.

Bowers, C. W.↗
NASA NTRS1987

Air- and oxygen-broadening coefficients for the O2 rotational line at 60.46/cm

Using an NBS laser-based tunable far-infrared spectrometer, the air- and oxygen-broadening coefficients were measured for the J = 10 - 10, N = 11 - 9 O2 rotational transition at 60.46/cm (1.812 THz). The air-broadening coefficient is 5.04 + or - 0.38 x 10 to the -7th/cm/Pa (0.0511 + or - 0.0039/cm/atm) (HWHM) at 245 + or - 6 K; the oxygen-broadening coefficient is 4.92 + or - 0.47 x 10 to the -7th/cm/Pa (0.0499 + or - 0.0048/cm/atm) (HWHM) at 259 + or -2 K. These direct experimental measurements of the air-broadening coefficient should improve the accuracy of retrieval calculations for far-infrared stratospheric balloon experiments which use O2 rotational lines to calibrate the viewing geometry.

Jennings, D. A.↗
NASA NTRS1988

Summary of along-track data from the Earth radiation budget satellite for several major desert regions

For several days in January and August 1985, the Earth Radiation Budget Satellite, a component of the Earth Radiation Budget Experiment (ERBE), was operated in an along-track scanning mode. A survey of radiance measurements is given for four desert areas in Africa, the Arabian Peninsula, Australia, and the Sahel region of Africa. Each overflight provides radiance information for four scene categories: clear, partly cloudy, mostly cloudy, and overcast. The data presented include the variation of radiance in each scene classification as a function of viewing zenith angle during each overflight of the five target areas. Several features of interest in the development of anisotropic models are evident, including day-night differences in longwave limb darkening and the azimuthal dependence of short wave radiance. There is some evidence that surface features may introduce thermal or visible shadowing that is not incorporated in the usual descriptions of the anisotropic behavior of radiance as viewed from space. The data also demonstrate that the ERBE scene classification algorithms give results that, at least for desert surfaces, are a function of viewing geometry.

Brooks, David R.↗
NASA NTRS1988

Impact of tracking network variation on GPS orbit determination

The accuracy of GPS orbit determination using a continental U.S. tracking network is limited by the localized viewing geometry. Substantial improvement can be gained when supplementary receiving sites are added outside the continental U.S. Covariance analysis shows that, when GPS pseudo-range data are used, adding a site at either Yellowknife in western Canada, or Fairbanks, Alaska, improves the orbits by about 25 percent. A supplementary network of two stations in the Australia/New Zealand region can improve GPS orbit accuracy by a factor of two. Adding Hawaii to a combined U.S. and Australia/New Zealand network improves the accuracy further, to a factor of three over the nominal U.S. network. With GPS carrier phase data, the improvement is not as great; adding Hawaii and Australia/New Zealand to the nominal U.S. network improves orbit accuracy by a factor of two.

Wu, S. C.↗
NASA NTRS1988

C-smithing of Voyager 2 non-imaging instrument pointing information at Uranus

The development of a family of techniques, collectively called C-smithing, for improving spacecraft nonimaging instrument pointing knowledge is discussed. C-smithing studies using data from the Voyager 2 Uranus Encounter show that significant improvements in pointing knowledge for nonimaging instruments can be achieved with these techniques. This improved pointing information can be used to regenerate instrument viewing geometry parameters for the encounter, which can then be made available to science investigators.

Wang, Tseng-Chan↗
NASA NTRS1988

The observed day-to-day variability of Mars atmospheric water vapor

The present evaluation of Viking water column abundance measurements of the Martian atmosphere notes observed changes to be due to atmospheric water vapor vertical column abundance variations, as well as to apparent changes resulting from abundance changes of atmospheric aerosols, relative vertical distribution changes of water vapor and aerosol, or systematic viewing-geometry variations. Variability noted in several major regions by visible and thermal-IR observations is found to very accurately coincide with the occurrence of water ice clouds and hazes.

Jakosky, Bruce M.↗