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NASA NTRS1982

Forward scattering and backscattering of solar radiation by the stratospheric limb after Mount St. Helens eruption

Stratospheric limb radiance profiles versus altitude of closest approach of the line of sight to the Earth's surface have been measured before and after the Mount St. Helens eruptions by means of photographs taken from a Sun-oriented balloon gondola floating above 35 km altitude over France. Preliminary data were reported for flights in October 1979 and in May and June 1980. The radiance integrated along the line of sight as in-situ radiance (R) can be derived taking into account absorption by ozone and air. The onion peeling inversion method was used to derive the vertical radiance (R) profiles respectively. The values of R were determined in the solar azimuth. The solar elevation angles are chosen larger for the backscattering observation than for the forward scattering observation to deal with as similar illumination conditions as possible despite the Earth's sphericity.

Ackerman, M.↗

NASA NTRS1982

Multitemporal and geobotanical approach in the remote detection of Greisenization areas in the Serra da Pedra Branca Granite, Goias State, Brazil

A multiseasonal analysis of LANDSAT multispectral images in CCT format permitted the mapping of lithologic facies in the Pedra Branca Granite, using geobotanical associations, which occur in the form of variations in the density of the cerrado vegetation, as well as the predominance of certain distinct vegetation species. Dry season images did not show very good results in lithological differentiation due to anomalous illumination conditions related to the low solar elevation and the homogeneity in the vegetation cover, specially the grass that becomes dry during this season. Rainy season images, on the other hand, allowed the separation of the lithological types, a fact that can be attributed to a greater differentiation among the geobotanical associations. The muscovite-granite facies with greisenization zones within the Serra da Pedra Branca were mapped. This methodology can be successfully applied to similar known granite bodies elsewhere in the Tin Province of Goias.

Parada, N. D. J.↗

NASA NTRS1982

Thermal structure of the atmosphere of Venus from Pioneer Venus radio occultations

The processing and analysis results from 87 radio occultation experiments performed with the Pioneer Venus Orbiter are detailed. Atmospheric structure data were obtained with S-band (2293 MHz) and X-band (8407 MHz) signals transmitted through the 40 and 85 km levels of the Venus atmosphere. Latitudes of -68 to 88 deg at solar zenith angles of 8-166 deg were explored. The conversion of the data into acceptable form for the barometric equation to use the perfect gas law to obtain the temperature profiles is described. The temperature structures were more dependent on latitude than solar illumination conditions, with the greatest changes occurring in the circumpolar region. The polar tropopause altitude was about 4.8 km above its value at lower altitudes, with a temperature drop of 60 K and a pressure drop of 240 mb.

Kliore, A. J.↗

NASA NTRS1983

Multiseasonal and geobotanical approach in remote detection of greisenization areas in the Serra da Pedra Branca Granite, Goias State, Brazil

Multiseasonal analysis of LANDSAT multispectral images in CCT format permitted the mapping of lithologic facies in the Pedra Branca Granite, using geobotanical associations, which occur in the form of variations in the density of cerrado vegetation, as well as the predominance of certain distinctive vegetation species. Dry season images did not show very good results in lithological differentiation due to anomalous illumination conditions related to the low solar elevation and the homogeneity in the vegetation cover, specially the grasses that become dry during this season. Rainy season image, on the other hand, allowed the separation of the lithological types, a fact that can be attributed to a greater differentiation among the geobotanical associations. As a result of this study, the muscovite-granite facies with greisenization zones, which are lithological indicators of important tin mineralization within the Serra da Pedra Branca Granite, were mapped. This methodology can be sucessfully applied to similar known granite bodies elsewhere in the Tin Province of Goias.

Parada, N. D. J.↗

NASA NTRS1984

Analysis of LANDSAT-4 TM Data for Lithologic and Image Mapping Purpose

Lithologic mapping techniques using the near infrared bands of the Thematic Mapper onboard the LANDSAT 4 satellite are investigated. These methods are coupled with digital masking to test the capability of mapping geologic materials. Data are examined under medium to low Sun angle illumination conditions to determine the detection limits of materials with absorption features. Several detection anomalies are observed and explained.

Podwysocki, M. H.↗

NASA NTRS1984

Red and near-infrared sensor response to off-nadir viewing

It has first been intended to employ the Advanced Very High Resolution Radiometer (AVHRR) as a meteorological instrument to aid in detecting clouds and atmospheric temperature stratifications over large areas. However, more recently the satellite data have been used for monitoring large areas of vegetation with emphasis on the visible (VIS) and near-infrared (NIR) bands. The present investigation is concerned with the objective to model ranges in AVHRR VIS and NIR radiances and normalized differences expected under typical AVHRR viewing and illumination conditions. Atmospheric data sets reported by Dave (1978) and Dave and Braslau (1975) were used. It is shown that sensor response to atmospheric path length can be substantial for the AVHRR VIS and NIR channels and normalized difference (ND) values. However, errors can be minimized by high sun and clear atmosphere viewing.

Holben, B.↗

NASA NTRS1985

Measurement and analysis of solar cell current-voltage characteristics

Approaches to measurement and analysis of solar cell current-voltage characteristics under dark and illuminated conditions are discussed. Measurements are taken with a computer based data acquisition system for temperatures in the range of -100 to +100 C. In the fitting procedure, the various I(oi) and C(i) as well as R(S) and R(SH) are determined. Application to current-voltage analyses of high efficiency silicon cells and Boeing CdS/CuInSe2 are discussed. In silicon MINP cells, it is found that at low voltages a tunneling mechanism is dominant, while at larger voltages the I-V characteristics are usually dominated by emitter recombination. In the case of Boeing cells, a current transport model based on a tunneling mechanism and interface recombination acting in series has been developed as a result of I-V analyses.

Olsen, Larry C.↗

NASA NTRS1987

Hydrogen Balmer alpha intensity distributions and line profiles from multiple scattering theory using realistic geocoronal models

The H Balmer alpha nightglow is investigated by using Monte Carlo models of asymmetric geocoronal atomic hydrogen distributions as input to a radiative transfer model of solar Lyman-beta radiation in the thermosphere and atmosphere. It is shown that it is essential to include multiple scattering of Lyman-beta radiation in the interpretation of Balmer alpha airglow data. Observations of diurnal variation in the Balmer alpha airglow showing slightly greater intensities in the morning relative to evening are consistent with theory. No evidence is found for anything other than a single sinusoidal diurnal variation of exobase density. Dramatic changes in effective temperature derived from the observed Balmer alpha line profiles are expected on the basis of changing illumination conditions in the thermosphere and exosphere as different regions of the sky are scanned.

Anderson, D. E., Jr.↗

NASA NTRS1987

Ground testing of array modules for the photovoltaic array space power (PASP) experiment

One of the objectives of the PASP experiment is the verification of cost-effective ground simulations of high-voltage solar array/space-environment interactions by comparing the results with flight data. These ground tests consist of electrical characterization, thermal cycling, and plasma chamber simulations. The results of the latter tests are reported. Five array modules which are representative of the flight arrays were tested. The module types are planar silicon, planar gallium arsenide, planar silicon passivated with an integrally deposited cover glass, mini-Cassegrainian concentrator, and SLATS concentrator. The modules were biased to -1000 V in varying plasma densities from 4 x 103 to 2 x 105 e-/cu cm. Each array was tested in both dark and illuminated conditions with a load resistance. In addition to monitoring arcing during the plasma tests, the arrays were visually inspected and electrically characterized before and after exposure in the chamber. The electrical results are tabulated and briefly discussed.

Morris, Robert K.↗

NASA NTRS1988

Photochemical modeling of the Antarctic stratosphere: Observational constraints from the airborne Antarctic ozone experiment and implications for ozone behavior

The rapid decrease in O3 column densities observed during Antarctic spring has been attributed to several chemical mechanisms involving nitrogen, bromine, or chlorine species, to dynamical mechanisms, or to a combination of the above. Chlorine-related theories, in particular, predict greatly elevated concentrations of ClO and OClO and suppressed abundances of NO2 below 22 km. The heterogeneous reactions and phase transitions proposed by these theories could also impact the concentrations of HCl, ClNO3 and HNO3 in this region. Observations of the above species have been carried out from the ground by the National Ozone Expedition (NOZE-I, 1986, and NOZE-II, 1987), and from aircrafts by the Airborne Antarctic Ozone Experiment (AAOE) during the austral spring of 1987. Observations of aerosol concentrations, size distribution and backscattering ratio from AAOE, and of aerosol extinction coefficients from the SAM-II satellite can also be used to deduce the altitude and temporal behavior of surfaces which catalyze heterogeneous mechanisms. All these observations provide important constraints on the photochemical processes suggested for the spring Antarctic stratosphere. Results are presented for the concentrations and time development of key trace gases in the Antarctic stratosphere, utilizing the AER photochemical model. This model includes complete gas-phase photochemistry, as well as heterogeneous reactions. Heterogeneous chemistry is parameterized in terms of surface concentrations of aerosols, collision frequencies between gas molecules and aerosol surfaces, concentrations of HCl/H2O in the frozen particles, and probability of reaction per collision (gamma). Values of gamma are taken from the latest laboratory measurements. The heterogeneous chemistry and phase transitions are assumed to occur between 12 and 22 km. The behavior of trace species at higher altitudes is calculated by the AER 2-D model without heterogeneous chemistry. Calculations are performed for solar illumination conditions typical of 60, 70, and 80 S, from July 15 to October 31.

Rodriguez, Jose M.↗

NASA NTRS1988

Monocular electro-optical stereo scanner

MEOSS is a single optics and single spectral band camera. Three CCD's working in pushbroom mode are mounted perpendicular to the flight direction on a common focal plate. Their oblique views of + and - 23 degrees forward and backward, as well as nadir oriented, lead to threefold stereoscopic images. This principle allows a nearly simultaneous generation of all three images of a stereo triplet. The time gap between the forward and aft looking images guarantees constant illumination conditions. The ground resolution of MEOSS will be 52 by 80 m ground pixel size, height resolution of 55 m and swath width of 255 km. The drifting ground coverage pattern of MEOSS is unique compared to polar orbiting satellites and will allow images of an area to be taken at different times of the day. A scene will consist of 3144 scan lines, with each having 3236 pixels. The data will be received by the Deep Space Network of JPL Goldstone and mailed to Goddard.

Vermillion, C.↗

NASA NTRS1988

Millimeter-wave diode-grid frequency doubler

Monolithic diode grids were fabricated on 2-cm square gallium-arsenide wafers in a proof-of-principle test of a quasi-optical varactor millimeter-wave frequency multiplier array concept. An equivalent circuit model based on a transmission-line analysis of plane wave illumination was applied to predict the array performance. The doubler experiments were performed under far-field illumination conditions. A second-harmonic conversion efficiency of 9.5 percent and output powers of 0.5 W were achieved at 66 GHz when the diode grid was pumped with a pulsed source at 33 GHz. This grid had 760 Schottky-barrier varactor diodes. The average series resistance was 27 ohms, the minimum capacitance was 18 fF at a reverse breakdown voltage of -3 V. The measurements indicate that the diode grid is a feasible device for generating watt-level powers at millimeter frequencies and that substantial improvement is possible by improving the diode breakdown voltage.

Jou, Christina F.↗

NASA NTRS1989

Estimation of properties of alpine snow from Landsat Thematic Mapper

On the basis of a simulation of a range of snow types and various atmospheric profiles in a variety of possible illumination conditions, it has proven possible to develop typical spectral signatures above the atmosphere over mountainous terrain. Landsat TM data of the southern Sierra Nevada are presently analyzed to distinguish several classes of snow from other surface covers. It is found that snow can be reliably mapped at all sun angles encountered in the midlatitudes, and that large surface grain sizes can be distinguished from areas where the grain size is finer at the snow surface.

Dozier, Jeff↗

NASA NTRS1989

Spectral signature of alpine snow cover from the Landsat Thematic Mapper

In rugged terrain, snow in the shadows can appear darker than soil or vegetation in the sunlight, making it difficult to interpret satellite data images of rugged terrains. This paper discusses methods for using Thematic Mapper (TM) and SPOT data for automatic analyses of alpine snow cover. Typical spectral signatures of the Landsat TM are analyzed for a range of snow types, atmospheric profiles, and topographic illumination conditions. A number of TM images of Sierra Nevada are analyzed to distinguish several classes of snow from other surface covers.

Dozier, Jeff↗

NASA NTRS1991

InP/Ga0.47In0.53As monolithic, two-junction, three-terminal tandem solar cells

The work presented has focussed on increasing the efficiency of InP-based solar cells through the development of a high-performance InP/Ga(0.47)In(0.53)As two-junction, three-terminal monolithic tandem cell. Such a tandem is particularly suited to space applications where a radiation-hard top cell (i.e., InP) is required. Furthermore, the InP/Ga(0.47)In(0.53)As materials system is lattice matched and offers a top cell/bottom cell bandgap differential (0.60 eV at 300 K) suitable for high tandem cell efficiencies under AMO illumination. A three-terminal configuration was chosen since it allows for independent power collection from each subcell in the monolithic stack, thus minimizing the adverse impact of radiation damage on the overall tandem efficiency. Realistic computer modeling calculations predict an efficiency boost of 7 to 11 percent from the Ga(0.47)In(0.53)As bottom cell under AMO illumination (25 C) for concentration ratios in the 1 to 1000 range. Thus, practical AMO efficiencies of 25 to 32 percent appear possible with the InP/Ga(0.47)In(0.53)As tandem cell. Prototype n/p/n InP/Ga(0.47)In(0.53)As monolithic tandem cells were fabricated and tested successfully. Using an aperture to define the illuminated areas, efficiency measurements performed on a non-optimized device under standard global illumination conditions (25 C) with no antireflection coating (ARC) give 12.2 percent for the InP top cell and 3.2 percent for the Ga(0.47)In(0.53)As bottom cell, yielding an overall tandem efficiency of 15.4 percent. With an ARC, the tandem efficiency could reach approximately 22 percent global and approximately 20 percent AMO. Additional details regarding the performance of individual InP and Ga(0.47)In(0.53)As component cells, fabrication and operation of complete tandem cells and methods for improving the tandem cell performance, are also discussed.

Wanlaas, M. W.↗

NASA NTRS1991

Investigation of varying gray scale levels for remote manipulation

A study was conducted to investigate the effects of variant monitor gray scale levels and workplace illumination levels on operators' ability to discriminate between different colors on a monochrome monitor. It was determined that 8-gray scale viewing resulted in significantly worse discrimination performance compared to 16- and 32-gray scale viewing and that there was only a negligible difference found between 16 and 32 shades of gray. Therefore, it is recommended that monitors used while performing remote manipulation tasks have 16 or above shades of gray since this evaluation has found levels lower than this to be unacceptable for color discrimination task. There was no significant performance difference found between a high and a low workplace illumination condition. Further analysis was conducted to determine which specific combinations of colors can be used in conjunction with each other to ensure errorfree color coding/brightness discrimination performance while viewing a monochrome monitor. It was found that 92 three-color combination and 9 four-color combinations could be used with 100 percent accuracy. The results can help to determine which gray scale levels should be provided on monochrome monitors as well as which colors to use to ensure the maximal performance of remotely-viewed color discrimination/coding tasks.

Bierschwale, John M.↗

NASA NTRS1989

Solar surface albedo estimation using remotely sensed spectral data

A solar albedo model based on converting narrow-band satellite-derived reflectance to four major spectral regions (ultraviolet, visible, near-infrared, and shortwave middle-infrared) and weighted by the relative supply of global solar radiation is studied and developed. Narrow-band to broad-band conversions within visible and near-infrared regions are shown to be accurate; however, the transformations are indicated to be surface-feature dependent. Atmospheric aerosol and illumination effects are indicated to be nearly insensitive to spectral region integrations for solar albedo estimation, but are shown to be significant factors affecting the spectral and canopy albedo. The erectophile and spherical canopy albedos were sensitive to atmospheric and illumination condition, whereas the planophile was relatively insensitive. The contribution of a shortwave middle-infrared reflectance to the canopy albedo is shown to be an important component, accounting for albedo changes to 16 percent with increasing vegetation.

Toll, David L.↗

NASA NTRS1991

Calculated sensitivities of several optical radiometric indices for vegetation canopies

The present study employs a radiative transfer model for a vegetation canopy to compute several quantities used in remote sensing applications and to determine the sensitivity of these radiometric quantities to several of the important problem parameters. Attention is given to the ratio of near IR to visible reflected intensities in the nadir direction, the ratio of the fraction of incident energy reflected in the near IR to that in the visible, the normalized difference between the near IR and visible nadir-reflected intensities, and the visible intensity transmitted in a given downward direction. A realistic radiative transfer model is proposed for calculating these radiometric quantities. With these models, the sensitivity of the reflected and transmitted quantities to various canopy and illumination conditions are then determined. The sensitivity of the calculated quantities are presented as a function of the leaf area index of the canopy, and, for the reflected quantities, also as a function of the fraction of visible light absorbed in the canopy.

Shultis, J. K.↗