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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Retrieval of aerosol optical characteristics from polarization measurements of reflected solar radiation above the oceans

The reflected near infrared solar radiation observed from space above the oceans is due mainly to the atmosphere scattering, as the ocean surface is nearly black. The molecular Rayleigh contribution is also minimized at infrared wavelengths and it can be evaluated. It is shown that the degree of polarization is much more sensitive to the aerosol properties than the radiance. Measurements of polarization at two wavelengths and with an angular scanning are simulated and an inversion algorithm is proposed. It aims at finding an 'equivalent aerosol model', which reproduces the optical thickness and the asymmetry factor of the actual aerosol at all wavelengths in the solar spectrum.

Santer, R.↗
NASA NTRS1984

Rapid extraction of relative topography from Viking orbiter images. 2: Application to irregular topographic features

The ratio and flat field photoclinometric methods for determining crater form topography are described. Both methods compensate for the effects of atmospheric scattering by subtracting a haze value from all brightness values. Algorithms were altered to derive relative topographic data for irregular features such as ejecta blankets, lava flows, graben and ridge scarps, dune forms, and stratified materials. After the elevations along the profiles are obtained by integration of the photometric function, a matrix transformation is applied to the image coordinates of each pixel within each profile, utilizing each pixel's integral height, to produce a projection of each profile line onto the surface. Pixel brightness values are then resampled along the projected track of each profile to determine a more correct height value for each pixel. Precision of the methods is discussed.

Davis, P. A.↗
NASA NTRS1984

Relative radiometric calibration of LANDSAT TM reflective bands

Raw thematic mapper (TM) calibration data from pre-launch tests and in-orbit acquisitions from LANDSAT 4 and 5 satellites are analyzed to assess the radiometric characteristics of the TM sensor. A software program called TM radiometric and algorithmic performance program (TRAPP) was used for the majority of analyses. Radiometric uncertainty in the final TM image originates from: (1) scene variability (solar irradiance and atmospheric scattering); (2) optical and electrical variability of the sensor; and (3) variability introduced during image processing.

Barker, J. L.↗
NASA NTRS1984

Auroral photometry from the atmosphere Explorer satellite

Attention is given to the ability of remote sensing from space to yield quantitative auroral and ionospheric parametrers, in view of the auroral measurements made during two passes of the Explorer C satellite over the Poker Flat Optical Observatory and the Chatanika Radar Facility. The emission rate of the N2(+) 4278 A band computed from intensity measurements of energetic auroral electrons has tracked the same spetral feature that was measured remotely from the satellite over two decades of intensity, providing a stringent test for the measurement of atmospheric scattering effects. It also verifies the absolute intensity with respect to ground-based photometric measurements. In situ satellite measurments of ion densities and ground based electron density profile radar measurements provide a consistent picture of the ionospheric response to auroral input, while also predicting the observed optical emission rate.

Rees, M. H.↗
NASA NTRS1983

Scan angle dependence of radiance recorded by the NOAA-AVHRR

NOAA-AVHRR data is being used to monitor global vegetation type and condition and to study various environmental factors in addition to performance of meteorological functions. The AVHRR instrument has + or - 54 deg as maximum scan angle limits and it is necessary to be aware of the effects of sun-target-sensor geometry at extreme scan angles to be able to properly interpret the satellite images. In order to interpret the images for vegetation type and condition analysis, it is necessary to calibrate back to the nadir view position. Both simulation studies and empirical investigations with digital scanner data have been performed in order to sufficiently understand the effects of scan angle and sun angle, as well as the effects of atmospheric scattering, to eventually perform adequate calibrations. Not surprisingly, the effects are large and studies are continuing to provide improved calibrations.

Duggin, M. J.↗
NASA NTRS1984

Mars polar volatiles: Topographic and geologic setting

Progress on a project to elucidate the geological and topographic setting of the Martian polar volatiles is reported. The following accomplishments are enumerated: (1) all of the Mariner 9 imaging data sets available through JPL were acquired and copied; (2) Mariner 9 imagery was investigated in terms of the accuracy of the imaging footprints, dark current, and residual image; (3) the transfer functions of both vidicons were investigated; and (4) the magnitude of the atmospheric scattering was examined.

Murray, B.↗
NASA NTRS1985

Atmospheric transmittance from spacecraft using multiple view angle imagery

A procedure for determining atmospheric transmittance using surface images acquired at several view angles from space is presented. Fourier filtering of the image data is used to mitigate the effects of atmospheric path radiance and instrument noise. Although it is essential for some contrast to be present in the images, knowledge of the atmospheric scattering phase function or the surface bidirectional reflectance function is not required. The method appears to provide absolute transmittances with an accuracy of better than 10 percent, which is useful in some applications.

Diner, D. J.↗
NASA NTRS1986

Non-Lambertian effects on remote sensing of surface reflectance and vegetation index

This paper discusses the effects of non-Lambertian reflection from a homogeneous surface on remote sensing of the surface reflectance and vegetation index from a satellite. Remote measurement of the surface characteristics is perturbed by atmospheric scattering of sun light. This scattering tends to smooth the angular dependence of non-Lambertian surface reflectances, an effect that is not present in the case of Lambertian surfaces. This effect is calculated to test the validity of a Lambertian assumption used in remote sensing. For the three types of vegetations considered in this study, the assumption of Lambertian surface can be used satisfactorily in the derivation of surface reflectance from remotely measured radiance for a view angle outside the backscattering region. Within the backscattering region, however, the use of the assumption can result in a considerable error in the derived surface reflectance. Accuracy also deteriorates with increasing solar zenith angle. The angular distribution of the surface reflectance derived from remote measurements is smoother than that at the surface. The effect of surface non-Lambertianity on remote sensing of vegetation index is very weak. Since the effect is similiar in the visible and near infrared part of the solar spectrum for the vegetations treated in this study, it is canceled in deriving the vegetation index. The effect of the diffuse skylight on surface reflectance measurements at ground level is also discussed.

Lee, T. Y.↗
NASA NTRS1987

Thematic mapper research in the earth sciences: Small scale patches of suspended matter and phytoplankton in the Elbe River Estuary, German Bight and Tidal Flats

A Thematic Mapper (TM) field experiment was followed by a data analysis to determine TM capabilities for analysis of suspended matter and phytoplankton. Factor analysis showed that suspended matter concentration, atmospheric scattering, and sea surface temperature can be retrieved as independent factors which determine the variation in the TM data over water areas. Spectral channels in the near infrared open the possibility of determining the Angstrom exponent better than for the coastal zone color scanner. The suspended matter distribution may then be calculated by the absolute radiance of channel 2 or 3 or the ratio of both. There is no indication of whether separation of chlorophyll is possible. The distribution of suspended matter and sea surface temperature can be observed with the expected fine structure. A good correlation between water depth and suspended matter distribution as found from ship data can now be analyzed for an entire area by the synoptic view of the TM scenes.

Grassl, H.↗
NASA NTRS1988

Latitudinal variation of thermospheric hydrogen near solstice from AE-D observations

Variations of thermospheric neutral atomic hydrogen with latitude during a solstice season near solar minimum were investigated using data acquired with the polar-orbiting AE-D satellite. Hydrogen concentrations at low latitude were found to be comparable to those found from observations with the AE-E satellite, but were slightly higher than concentrations derived from the 1983 mass spectrometer incoherent scatter atmospheric model. Results confirm the general summer-to-winter density increase, large latitudinal gradients in the summer hemisphere, and the winter enhancement of hydrogen observed in AE-C nighttime measurements. The AE-D data, however, show a small polar depression in hydrogen concentration at high winter latitudes, attributed to atmospheric dynamics following auroral heating. The density gradients observed by AE-D in the summer hemisphere were in sharp contrast to the more constant horizontal daytime profiles reported from OGO-6 and previous AE-C measurements, indicating the possibility of local time effects.

Sanatani, S.↗
NASA NTRS1989

The far ultraviolet reflection spectrum of Uranus - Results from the Voyager encounter

The present analysis of the 1250-1700 A region Uranus spectrum obtained by Voyager's US spectrometer characterizes these observation results as due primarily to solar light reflected from an H2 Rayleigh and Raman scattering atmosphere with small but measurable hydrocarbon absorption. The hydrocarbon abundances obtained are substantially lower than those at comparable levels of the Saturn or Jupiter atmospheres; it is suggested, in one-dimensional terms, that this is due to diffusive separation, in conjunction with photochemical depletion caused by a very low eddy-diffusion coefficient. Strong latitudinal variations in the hydrocarbon abundances are suggested in the subsolar, polar stratosphere.

Yelle, Roger V.↗
NASA NTRS1989

Small scale patches of suspended matter and phytoplankton in the Elbe River estuary, German Bight and tidal flats

Landsat 5 TM measurements are found suitable for study of small scale features in coastal waters; three independent factors, namely suspended matter concentration, atmospheric scattering, and sea-surface temperature, were extracted from all seven TM channels on the basis of factor analysis. The distribution of suspended matter in near-surface water layer and sea surface temperature is observable with a spatial resolution of at least 120 x 120 sq m. The high correlation between water depth and suspended matter distribution established by ship-gathered data supports the presently hypothesized control by bottom topography and wind-modified tidal currents of eddy and front formation.

Doerffer, R.↗
NASA NTRS1990

Gaussian quadrature exponential sum modeling of near infrared methane laboratory spectra obtained at temperatures from 106 to 297 K

Transmission measurements made on near-infrared laboratory methane spectra have previously been fit using a Malkmus band model. The laboratory spectra were obtained in three groups at temperatures averaging 112, 188, and 295 K; band model fitting was done separately for each temperature group. These band model parameters cannot be used directly in scattering atmosphere model computations, so an exponential sum model is being developed which includes pressure and temperature fitting parameters. The goal is to obtain model parameters by least square fits at 10/cm intervals from 3800 to 9100/cm. These results will be useful in the interpretation of current planetary spectra and also NIMS spectra of Jupiter anticipated from the Galileo mission.

Giver, Lawrence P.↗
NASA NTRS1989

Thomson scattering in magnetic fields

The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.

Whitney, Barbara↗
NASA NTRS1990

Long-range sound propagation: A review of some experimental data

Three experimental studies of long range sound propagation carried out or sponsored in the past by NASA are briefly reviewed to provide a partial prospective for some of the analytical studies presented in this symposium. The three studies reviewed cover (1) a unique test of two large rocket engines conducted in such a way as to provide an indication of possible atmospheric scattering loss from a large low-frequency directive sound source, (2) a year-long measurement of low frequency sound propagation which clearly demonstrated the dominant influence of the vertical gradient in the vector sound velocity towards the receiver in defining excess sound attenuation due to refraction, and (3), a series of excess ground attenuation measurements over grass and asphalt surfaces replicated several times under very similar inversion weather conditions.

Sutherland, Louis C.↗
NASA NTRS1992

Preliminary calibration results for the BATSE instrument on CGRO

Preliminary results pertaining to spectral reconstruction using Burst and Transient Source (BATSE) Large Area Detector measurements of solar flares are presented. The solar flare measurements are currently being used to fine tune the calibration of our data analysis software. The current status of the stability of spectral analysis, given the systematic errors present in burst location, are given. A brief description is given of enhancements to the input data for the atmospheric scattering algorithm that will be implemented in the data analysis software.

Pendleton, G. N.↗
NASA NTRS1992

Aerosol optical depth retrievals over the Konza Prairie

The aerosol optical depth over the Konza Prairie, near Manhattan, Kansas, was recorded at various locations by five separate teams. These measurements were made in support of the First ISLSCP Field Experiment (FIFE) and used to correct imagery from a variety of satellite and aircraft sensors for the effects of atmospheric scattering and absorption. The results from one instrument are reported here for 26 days in 1987 and for 7 in 1989. Daily averages span a range of 0.05 to 0.28 in the midvisible wavelengths. In addition, diurnal variations are noted in which the afternoon optical depths are greater than those of the morning by as much as 0.07. A comparison between instruments and processing techniques used to determine these aerosol optical depths is provided. The first comparisons are made using summer 1987 data. Differences of as much as 0.05 (midvisible) are observed. Although these data allow reasonable surface reflectance retrievals, they do not agree to within the performance limits typically associated with these types of instruments. With an accuracy goal of 0.02 a preseason calibration/comparison experiment was conducted at a mountain site prior to the final field campaign in 1989. Good calibration data were obtained, and good agreement (0.01, midvisible) was observed in the retrieved optical depth acquired over the Konza. By comparing data from the surface instruments at different locations, spatial inhomogeneities are determined. Then, data from the airborne tracking sunphotometer allow one to determine variations as a function of altitude. Finally, a technique is proposed for using the in situ data to establish an instrument calibration.

Bruegge, Carol J.↗
NASA NTRS1992

Preliminary burst location calibration results for the BATSE instrument on CGRO

Preliminary results pertaining to burst location using BATSE Large Area Detector measurements of solar flares are presented. These solar flare measurements are currently being used to fine tune the calibration of our data analysis software. The current status of techniques for identifying and eliminating systematic errors from the data analysis tools is discussed. Data revealing the effects of the atmospheric scattering algorithm that will be implemented in the data analysis software are presented.

Pendleton, G. N.↗