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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Atmospheric correction algorithm for NOAA-AVHRR products - Theory and application

The present evaluation of the effects of atmospheric constituents on NOAA AVHRR visible and near-IR data first gives attention to the general remote sensing equation and then addresses the magnitude of the atmospheric effects for AVHRR solar bands with respect to their impact on the normalized difference vegetation index (NDVI) and the surface bidirectional reflectance. Possible approaches to the acquisition of atmospheric data are then considered, and examples of atmospheric correction of surface reflectance and NDVI are discussed. The correction of the aerosol effect is essential in the case of NDVI study of densely vegetated areas.

Tanre, Didier↗
NASA NTRS1992

Atmospherically Resistant Vegetation Index (ARVI) for EOS-MODIS

ARVI, which is here proposed as a tool for the remote sensing of vegetation by the EOS MODIS sensor, takes advantage of the presence of the blue channel in MODIS, together with the red and near-IR channels composing the normalized-difference vegetation index (NDVI). Unlike the NDVI, ARVI resists atmospheric effects via a self-correction process for the effects of the atmosphere on the red channel. ARVI is presently shown to have a dynamic range similar to NDVI's, but is on average less sensitive to atmospheric effects by a factor of 4. A single combination of the blue and red channels in the ARVI may be used in all or most remote-sensing applications.

Kaufman, Yoram J.↗
NASA NTRS1992

Reflectance of snow as measured in situ and from space in sub-arctic areas in Canada and Alaska

An effort is made to measure snow reflectance under different snow and surface conditions, as well as to improve current capabilities for measuring snow reflectance over large regions of space, on the basis of visible and near-IR measurements of clean and dirty snow near Yellowknife, Canada, using both a portable spectrometer and the Landsat TM. Similar measurements were acquired over snow-covered glaciers in Alaska. Visible reflectance of the dirty snow was 30 percent lower than for cleaner snow; the shapes of the reflectance curves were also flatter for the dirty snow. The shape of the reflectance curves and the anisotropic reflectance properties are more useful in differentiating snow type and moisture type than actual reflectances.

Hall, D. K.↗
NASA NTRS1992

Discovery of a second narrow absorption feature in the near-infrared spectrum of Io

A high resolution survey of the near-IR reflectance spectrum of Io has shown a sharp absorption feature centered at 5045 +/- 1/cm; this feature is not present in laboratory spectra of dilute CO2 in a matrix. Since the spectrum of cold H2S ice crystals exhibits structure near this wavelength, it is suggested that either (1) the difference in width between this feature and that of the much broader Ionian H2S ice may be due to the presence of different phases of ice at different temperatures, so that these are emphasized in the different spectral regions, or (2) H2S is trapped in an SO2 matrix.

Lester, D. F.↗
NASA NTRS1991

Imaging spectroscopy of Mars during 1990

Preliminary results are presented of observations of Mars using three telescopes and a CCD camera, grating-array spectrometers, and a near-IR array camera. Martian albedo features are shown to be similar in the visible and 1.3-3.5-micron range, and reflectances of nearly zero are noted in the image at 3.02 microns. The results demonstrate that these techniques provide effective maps of spatial variations in spectral absorption features caused by Martian atmospheric volatiles and by surface minerals.

Bell, James F., III↗
NASA NTRS1992

The metallicity and luminosity of RV Tauri variables from medium-resolution spectra

Results are reported from spectroscopic observations of members of the RV Tauri class of pulsating variable stars at moderate resolution, and from photometric observations of these stars with the B and V filters of the Johnson UBV system and the first four filters of the Wing eight-color narrowband near-IR system. Of the 22 variables observed, TiO absorption was detected in eight, and 10 variables displayed hydrogen-line emission at some phase. Spectral classifications were assigned relative to the MK process. Color excesses were determined for those variables for which spectroscopic and photometric data were obtained within a few days of each other. The spectra obtained at a resolution of 2.5 A were fitted with synthetic spectra to determine the stellar atmospheric parameters. The range in metallicity among the variables was found to be quite extensive, -0.3 to -0.7, and may reflect a mixture of stellar populations or masses.

Wahlgren, Glenn M.↗
NASA NTRS1992

HARDI: A high angular resolution deployable interferometer for space

We describe here a proposed orbiting interferometer covering the UV, visible, and near-IR spectral ranges. With a 6-m baseline and a collecting area equivalent to about a 1.4 m diameter full aperture, this instrument will offer significant improvements in resolution over the Hubble Space Telescope, and complement the new generation of ground-based interferometers with much better limiting magnitude and spectral coverage. On the other hand, it has been designed as a considerably less ambitious project (one launch) than other current proposals. We believe that this concept is feasible given current technological capabilities, yet would serve to prove the concepts necessary for the much larger systems that must eventually be flown. The interferometer is of the Fizeau type. It therefore has a much larger field (for guiding) better UV throughout (only 4 surfaces) than phased arrays. Optimize aperture configurations and ideas for the cophasing and coalignment system are presented. The interferometer would be placed in a geosynchronous or sunsynchronous orbit to minimize thermal and mechanical disturbances and to maximize observing efficiency.

Bely, Pierre Y.↗
NASA NTRS1992

Venusian hydrology: Steady state reconsidered

In 1987, Grinspoon proposed that the data on hydrogen abundance, isotopic composition, and escape rate were consistent with the hypothesis that water on Venus might be in steady state rather than monotonic decline since the dawn of time. This conclusion was partially based on a derived water lifetime against nonthermal escape of approximately 10(exp 8) yr. De Bergh et al., preferring the earlier Pioneer Venus value of 200 ppm water to the significantly lower value detected by Bezard et al., found H2O lifetimes of greater than 10(exp 9) yr. Donahue and Hodges derived H2O lifetimes of 0.4-5 x 10 (exp 9) yr. Both these analyses used estimates of H escape flux between 0.4 x 10(exp 7) and 1 x 10(exp 7) cm(exp -2)s(exp -1) from Rodriguez et al. Yet in more recent Monte Carlo modeling, Hodges and Tinsley found an escape flux due to charge exchange with hot H(+) of 2.8 x 10(exp 7) cm(exp -2)s(exp -1). McElroy et al. estimated an escape flux of 8 x 10(exp 6) cm(exp -2)s(exp -1) from collisions with hot O produced by dissociative recombination of O2(+). Brace et al. estimated an escape flux of 5 x 10(exp 6) cm(exp -2)s(exp -1) from ion escape from the ionotail of Venus. The combined estimated escape flux from all these processes is approximately 4 x 10(exp 7) cm(exp -2)s(exp -1). The most sophisticated analysis to date of near-IR radiation from Venus' nightside reveals a water mixing ratio of approximately 30 ppm, suggesting a lifetime against escape for water of less than 10(exp 8) yr. Large uncertainties remain in these quantities, yet the data point toward a steady state. Further evaluation of these uncertainties, and new evolutionary modeling incorporating estimates of the outgassing rate from post-Magellan estimates of the volcanic resurfacing rate are presented.

Grinspoon, David H.↗
NASA NTRS1992

The evolution of the quasar continuum

We now have in hand a large data base of Roentgen Satellite (ROSAT), optical, and IR complementary data. We are in the process of obtaining a large amount of the International Ultraviolet Explorer (IUE) data for the same quasar sample. For our complementary sample at high redshifts, where the UV was redshifted into the optical, we have just had approved large amounts of observing time to cover the quasar continuum in the near-IR using the new Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) array spectrographs. Ten micron, optical, and VLA radio, data also have approved time. An ISO US key program was approved to extend this work into the far-IR, and the launch of ASTRO-D (early in 1993) promises to extend it to higher energy X-rays.

Elvis, M.↗
NASA NTRS1992

A spectral survey of the Serenitatis Basin region of the Moon

In recent years, we have utilized the Apollo orbital geochemistry datasets and Earth-based spectral reflectance data to investigate the composition of highland units associated with lunar multiring basins. These include Imbrium, Orientale, and Nectaris Basins. We have also analyzed a large number of near-IR reflectance spectra and multispectral images in an attempt to answer a variety of questions concerning the Serenitatis Basin. These questions include the following: (1) What is the composition of highland units in the region and how do these compositions vary as a function of position around and distance from Serenitatis?; (2) What was the crustal stratigraphy of the Serenitatis preimpact target site?; (3) How do the Apollo 17 samples relate to geologic units in the surrounding highlands?; (4) What is the nature and origin of light plains deposits in the region?; and (5) Do cryptomare occur in the Serenitatis region? The purpose of this paper is to present the preliminary results of our analyses of spectral data obtained for the Serenitatis Basin region.

Hawke, B. R.↗
NASA NTRS1992

Effects of the chemical environment on the spectroscopic properties of clays: Applications for Mars

Laboratory studies of Mars soil analogs pose unique problems, since soils interact readily with their environment and exhibit variable characteristics depending on the environment. We have performed a series of experiments focusing on the spectral properties of clays and how they vary as a function of composition and environment, including examination of fundamental as well as overtone absorptions, that occur in the mid- and near-IR, respectively. Smectite clays have been selected in our laboratory experiments as a primary surface analog for Mars because of their compatibility with results of the Viking biology experiments, their stability under current martian conditions, and their compatibility with reflectance spectra of Mars. We prepared a number of monoionic montmorillonites in order to examine the influence of cations on the water molecules in the clay interlayer region. Moessbauer spectra of several montmorillonites with variable amounts of interlayer iron confirm the presence of ferrihydrite.

Bishop, Janice L.↗
NASA NTRS1992

Optical spectroscopy of Z Canis Majoris, V1057 Cygni, and FU Orionis - Accretion disks and signatures of disk winds

High resolution, high SNR optical spectra have been used to investigate the hypothesis that in outburst, FU Ori objects are self-luminous accretion disks whose light dominates at optical and near-IR wavelengths. Strong evidence has been found for linewidth versus wavelength correlation in good agreement with model predictions for Z CMa and V1057 Cyg, but not for FU Ori itself. Linewidth varies continuously with wavelength at optical wavelengths in the former two objects, In the case of FU Ori, it is argued that a combination of strong wind components to spectral lines, and surface gravity possibly being lower than that of supergiants, conceals the underlying linewidth versus wavelength relationship. A marginal correlation is found between linewidth and lower excitation potential in all three objects. Synthetic disk spectra are subtracted from observed spectral, and remarkably good fits are found for all three objects for wavelengths longer than about 5000 A.

Welty, Alan D.↗
NASA NTRS1992

IRAS observations of young stellar objects in the Corona Australis dark cloud

The young stellar object (YSO) population associated with the dark cloud complex in Corona Australis is studied by synthesizing IRAS data with newly obtained near-IR and mid-IR photometry and previously published optical/IR data. Twenty-four YSOs in the Cr A complex are identified. The observed range of spectral energy distribution shapes and bolometric luminosities are consistent with those observed in other dark clouds. The duration and efficiency of star formation are found to be similar to the Rho Ophiuchi IR cluster. The low number of YSOs compared to other dark clouds is understood by a reevaluation of the molecular mass of the R Cr A cloud which shows it to be much less massive than previously assumed.

Wilking, Bruce A.↗
NASA NTRS1992

Scattering of infrared radiation by dust in NGC 7023 and NGC 2023

The contribution of scattered light to the total nebular emission is determined on the basis of linear polarization measurements at 1.25, 1.65, and 2.2 microns of the visual reflection nebulae NGC 7023 and NGC 2023. The percentage polarization of NGC 7023 slowly increases from 0.3 to 1 micron, with peak polarizations of up to 26 percent at 1.25 micron, then rapidly decreases, with values of 4-7 percent at 2.2 microns. This is interpreted as implying that scattered starlight contributes most to the SW emission, while unpolarized emission from small grains or large molecules dominates at longer wavelengths. IR polarization and surface brightness measurements are combined to derive the intensity of scattered light, which is then compared with scattering models. While the near-IR emission of both NGC 2023 and NGC 7023 is dominated by small-grain or large-molecule emission, IR scattered light plays a larger role in NGC 2023 than in NGC 7023.

Sellgren, K.↗
NASA NTRS1992

Relationship of E-type Apollo asteroid 3103 (1982 BB) to the enstatite achondrite meteorites and the Hungaria asteroids

Visible and near-IR observations are reported which confirm that Apollo asteroid 3103 (1982 BB) is a high-albedo E-type object with a reflectance spectrum consistent with the iron-free silicates, primarily enstatite, present in the aubrites. Visible and thermal IR light curves indicate that 3103 is an elongated object with no evidence of substantial surface albedo variations. It is presently in an orbital resonance with earth and is probably a relatively long-lived member of the earth-approaching population. This is consistent with the relatively long cosmic ray exposure ages of the aubrites compared to other stony meteorites. The fall geometries of the aubrites are consistent with their being derived from 3103. The ubiquitous brecciated nature of the aubrites and the indications of a single parent body for nearly all these meteorite suggest that 3103 is the sole near-earth parent body of this meteorite type.

Gaffey, Michael J.↗
NASA NTRS1991

Integration of optical and microwave images for geologic mapping and resource explorations

Multispectral images in the visible, near-IR, short-wave IR, thermal IR, and microwave regions, obtained during the Geologic Remote Sensing Field Experiment were combined with data from Landsat TM, laboratory, and field spectral measurements, as well as traditional geologic mapping and were used to produce thematic image maps showing details of the surface geology for an area at the north end of Death Valley (California/Nevada). The integrated multispectral images provide new geologic information which can be used in mineral deposit models to provide exploration targets. The data demonstrated the relationship between the surface composition of materials and remote sensing in the visible and infrared.

Kruse, Fred A.↗
NASA NTRS1991

Fiber optic and laser sensors IX; Proceedings of the Meeting, Boston, MA, Sept. 3-5, 1991

The present volume on fiber-optic and laser sensors discusses industrial applications of fiber-optic sensors, fiber-optic temperature sensors, fiber-optic current sensors, fiber-optic pressure/displacement/vibration sensors, and generic fiber-optic systems. Attention is given to a fiber-sensor design for turbine engines, fiber-optic remote Fourier transform IR spectroscopy, near-IR fiber-optic temperature sensors, and an intensity-type fiber-optic electric current sensor. Topics addressed include fiber-optic magnetic field sensors based on the Faraday effect in new materials, diaphragm size and sensitivity for fiber-optic pressure sensors, a microbend pressure sensor for high-temperature environments, and linear position sensing by light exchange between two lossy waveguides. Also discussed are two-mode elliptical-core fiber sensors for measurement of strain and temperature, a fiber-optic interferometric X-ray dosimeter, fiber-optic interferometric sensors using multimode fibers, and optical fiber sensing of corona discharges.

Depaula, Ramon P.↗
NASA NTRS1990

Planetary astronomy of Mars. Mars data reduction

Grant #NAGW-1408 was specifically awarded to obtain telescopic visible and near-IR spectral imaging of Mars during the 1988 apparition (9/28/88). The observing program was highly successful producing approximately 2 Gbytes of data, but was only funded for one year and virtually all of the funds were spent in data acquisition. The follow-up grant was funded the following year for reduction of these data into a scientifically productive form, which because of the size and nature of our observations, was a non-trivial task. A more detailed scientific analysis of these data (fully reduced) is in progress now and will take a number of years. Extended geologic analyses of the astronomical data are being funded by the NASA Planetary Geology and Geophysics program. The objective was to produce detailed reflectance spectra for contiguous, spatially resolved surface elements covering most of the planet (about +50 degrees to -90 degrees latitude, all longitudes). A total of 6 observing runs, of 3-4 days duration each, were conducted on the University of Arizona's 1.5m telescope on Mt. Bigelow. We present a sketch map showing the approximate total extent of our spectral image coverage. Nearly all of Mars south of 40 degrees N was observed at least once. About half of the area shown was observed multiple times. South of 65 degrees S, including the south polar cap, our coverage is heavily redundant. The first run was conducted June 29 - July 1, 1988 (all dates are UT) to serve as a baseline prior to possible dust storm activity on Mars. The other observing runs were closer to opposition: Sept. 3-6, 13-15, 24-26, and Oct. 5-7 and 16-18. The September and October observations were scheduled to provide maximum longitudinal coverage. This was also intended to provide a balance between surface observations and observations of predicted dust storm activity. No global dust storm developed in 1988, so we have a large volume of data for the surface of Mars.

Singer, Robert B.↗