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Smythe, W. D.

Publications and source records attributed to Smythe, W. D..

70 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Hermes Global Orbiter: A Discovery Mission in Gestation

The hermes Global Orbiter (HGO) is a Discovery class mission under study, which is investigating the possibility of placing a small spacecraft in highly elliptical polar orbit about mercury. The purpose of the mission is to conduct observations of the planet's surface, atmosphere and magnetosphere.

spacecraft Mercury orbit payload Delta II Venus fl↗
NASA NTRS1994

Galileo infrared imaging spectrometry measurements at the Moon

Imaging spectrometer observations were made of the surface of the Moon during the December 1990 flyby of the Earth-Moon system by the Galileo spacecraft. This article documents this data set and presents analyses of some of the data. The near infrared mapping spectrometer (NIMS) investigation obtained 17 separate mosaics of the Moon in 408 spectral channels between about 0.7 and 5.2 micrometers. The instrument was originally designed to operate in orbit about Jupiter and therefore saturates at many spectral channels for most measurement situations at 1 AU. However, sufficient measurements were made of the Moon to verify the proper operation of the instrument and to demonstrate its capabilities. Analysis of these data show that the NIMS worked as expected and produced measurements consistent with previous ground-based telescopic studies. These are the first imaging spectrometer measurements of this type from space for the Moon, and they illustrate several major points concerning this type of observation and about the NIMS capabilities specifically. Of major importance are the difference between framing and scanning instruments and the effects of the spacecraft and the scan platform on the performance of such and experiment. The science return of subsequent NIMS and other investigation measurements will be significantly enhanced by the experience and results gained.

Mccord, Thomas B.↗
NASA NTRS1993

Earth global mosaic observations with NIMS-Galileo

During the Earth-1 Galileo flyby (December 1990), the Near-Infrared Mapping Spectrometer (NIMS) experiment investigated the illuminated side of the Earth in the spectral range 0.7-5.2 micrometers. Mosaics of the entire terrestrial globe were recorded with a spatial resolution ranging from 100 to 500 km. From these spectra, information is retrieved upon the large-scale temperature structure in the stratosphere and in the mesosphere (0-70 km altitude range) from the inversion of the CO2 bands at 4.3 and 4.8 micrometers. These data also permit monitoring of the cloud temperatures, and derivation of the abundances of several minor atmospheric constituents (H2O, CO, N2O, CH4 and O3). These observations constitute a continuation of the study of the atmospheres of the three planets (i.e. Venus, the Earth and Jupiter) targeted by the Galileo spacecraft during its mission. Observing these atmospheres with the NIMS instrument in the near-infrared will provide a unique data set, useful for comparative planetary studies.

Drossart, P.↗
NASA NTRS1993

(abstract) Galileo NIMS Thermal Observations of Asteroid 951 Gaspra

The Near Infrared Mapping Spectrometer (NIMS) onboard the Galileo spacecraft performed spectral and thermal imaging of asteroid 951 Gaspra during the spacecraft flyby on October 29, 1991. Measurements of the hemispherically averaged temperature on Gaspra as the spacecraft approached the asteroid will also be reported. Differences resulting from other choices for thermophysical parameters in the model will be explored. Similar measurements are currently being planned for the Galileo encounter with asteroid 243 Ida, which will occur in late August of 1993.

asteroid near infrared imaging Galileo Gaspra Ida↗
NASA NTRS1993

The coherent backscattering opposition effect

We have measured the opposition effect, the nonlinear surge in reflectance seen in particulate materials as phase angle approaches zero degrees, in a suite of materials of varying particle size and reflectance. These samples were illuminated by linearly and circularly polarized monochromatic radiation at two wavelengths, 0.442 and 0.633 microns. By measuring the linear and circular polarization ratios for each sample, we have found that in highly reflective materials the behavior of the reflected radiation is consistent with the coherent backscattering process which has recently been proposed to explain the opposition surge that is seen in such media. The size and width of the coherent backscattering opposition peak vary as a function of reflectance of the sample. The opposition effect has been observed in particulate materials studied in the laboratory and it is also observed in the radiation reflected from solar system bodies which present a regolith to the earth based observer. The traditional explanation of the opposition effect, the shadow-hiding hypothesis, is that it was caused by the elimination of mutual shadows cast between the regolith grains as the phase angle of the observation became smaller. This shadow-hiding hypothesis, however, is unable to explain the opposition effect seen in highly reflective materials such as magnesium oxide and barium sulfate powders. This is because highly reflective media will multiply scatter the incident radiation between the regolith grains. This causes the shadows to be eliminated. We have measured the angular scattering properties of a suite of materials of different reflectivity. We have observed polarization ratios in reflective particulates that are consistent with coherent backscattering as the principal process which causes the opposition surge.

Nelson, R. M.↗
NASA NTRS1992

Near-Infrared Mapping Spectrometer experiment on Galileo

The Galileo Mission's Near-Infrared Mapping Spectrometer (NIMS) combines imaging and spectroscopic methods to map morphological features, ascertain their chemical composition and mineralogy, investigate surface-geology evolution, and measure the parameters of transient atmospheric phenomena. NIMS will investigate Jupiter and the Galilean satellites during a two-year orbital operation period, beginning in December, 1995. En route, NIMS will have obtained data for Venus, the earth/moon system, and two asteroids. NIMS covers the 0.7-5.2 micron spectral range, thereby encompassing the reflected-sunlight and thermal-radiation regimes for numerous solar system objects.

Carlson, R. W.↗
NASA NTRS1991

Galileo infrared imaging spectroscopy measurements at Venus

During the 1990 Galileo Venus flyby, the Near Infrared Mapping Spectrometer investigated the night-side atmosphere of Venus in the spectral range 0.7 to 5.2 micrometers. Multispectral images at high spatial resolution indicate substantial cloud opacity variations in the lower cloud levels, centered at 50 kilometers altitude. Zonal and meridional winds were derived for this level and are consistent with motion of the upper branch of a Hadley cell. Northern and southern hemisphere clouds appear to be markedly different. Spectral profiles were used to derive lower atmosphere abundances of water vapor and other species.

Carlson, R. W.↗
NASA NTRS1990

Spectral geometric albedo and bolometric Bond albedo of Neptune's satellite Triton from Voyager observations

The spectral geometric albedo and the bolometric Bond albedo of Triton are calculated using data from the Voyager spacecraft photopolarimeter and science experiments. The geometric albedo is not inconsistent with the presence of a weak absorption feature in Triton's spectrum near 0.75 micron. The bolometric Bond albedo (0.65) is consistent with the 38 K daytime surface temperature of Triton. The results are also in agreement with the 37.5 K temperature of nitrogen at an infrared basal pressure of 14 microbar.

Nelson, R. M.↗
NASA NTRS1986

Spectral reflectance of solid sulfur trioxide (0.25-5.2 micron) - Implications for Jupiter's satellite Io

Laboratory data on the UV and near-IR spectra of SO3 are compared with spectra obtained for the Jovian moon Io by the Voyager and IUE satellites. The experimental data were taken at wavelengths from 0.25 micron to nearly 6 microns, although only order-of-magnitude estimates could be made of the associated particle sizes. Tests were also performed to identify the spectral characteristics with succeedingly lower concentrations of SO3 relative to SO2, which is apparently abundant on the Io surface. No evidence was found for the presence of solid SO3 in the spectra of Io down to projected concentrations lower than 1 percent. The findings are considered surprising since it is known that particle bombardment will cause SO3 to form in SO2 concentrations. It is expected that SO3 will be detected by the IR mapping instrument to be carried by the Galileo spacecraft.

Nelson, R. M.↗
NASA NTRS1985

Sulfur Oxygen Processes on Io

The presence of allotropic sulfur as a possible major constituent of Io's surface and the properties of sulfur in combination with various sulfur-oxygen compounds believed to be present on Io's surface and in its atmosphere are studied by a series of laboratory experiments.

Nelson, R. M.↗