Engineering topics
Thompson, Thomas W.
Publications and source records attributed to Thompson, Thomas W..
Archived 1976-1985 JPL Aircraft SAR Data
This report describes archived data from the Jet Propulsion Laboratory (JPL) aircraft radar expeditions in the mid-1970s through the mid-1980s collected by Ron Blom, JPL Radar Geologist. The dataset was collected during Ron's career at JPL from the 1970s through 2015. Synthetic Aperture Radar (SAR) data in the 1970s and 1980s were recorded optically on long strips of film. SAR imagery was produced via an optical, holographic technique that resulted in long strips of film imagery.
Updated Model of Radar Backscatter for Rough Lunar Craters
We reexamined our radar scattering model for young, rough craters [1] based on unpublished data from the 1980's [2]. Our model for scattering from the lunar surface is a mixing model consisting of varying amounts of diffuse and specular components as shown in Figure 1. The specular component, which consists of only opposite-sense circular (OC) echoes, results from the mirror-like surface and sub-surface layers that are smooth to a tenth of a radar wavelength for large (>10 wavelengths) areas oriented perpendicular to the radar's line-ofsight. The diffuse component, which has both OC and same sense (SC) circular echoes, is associated with either surface roughness (wavelength-sized rocks) or ice, and is assumed to be uniformly bright, with backscatter being proportional to the cosine of the incidence angle. Only diffuse scattering contributes to the SC echoes.
Radar Probing of Planetary Regoliths: An Example from the Northern Rim of Imbrium Basin
Imaging radar measurements at long wavelengths (e.g., >30 cm) allow deep (up to tens of meters) probing of the physical structure and dielectric properties of planetary regoliths. We illustrate a potential application for a Mars orbital synthetic aperture radar (SAR) using new Earth-based 70-cm wavelength radar data for the Moon. The terrae on the northern margin of Mare Imbrium, the Montes Jura region, have diffuse radar backscatter echoes that are 2-4 times weaker at 3.8-cm, 70-cm, and 7.5-m wavelengths than most other lunar nearside terrae. Possible geologic explanations are (1) a pyroclastic deposit associated with sinuous rilles in this region, (2) buried mare basalt or a zone of mixed highland/basaltic debris (cryptomaria), or (3) layers of ejecta associated with the Iridum and Plato impacts that have fewer meter-sized rocks than typical highlands regolith. While radar data at 3.8-cm to 7.5-m wavelengths suggest significant differences between the Montes Jura region and typical highlands, the surface geochemistry and rock abundance inferred from Clementine UV-VIS data and eclipse thermal images are consistent with other lunar terrae. There is no evidence for enhanced iron abundance, expected for basaltic pyroclastic deposits, near the source vents of the sinuous rilles radial to Plato. The regions of low 70-cm radar return are consistent with overlapping concentric ''haloes'' about Iridum and Plato and do not occur referentially in topographically low areas, as is observed for radar-mapped cryptomaria. Thus we suggest that the extensive radar-dark area associated with the Montes Jura region is due to overlapping, rock-poor ejecta deposits from Iridum and Plato craters. Comparison of the radial extent of low-radar-return crater haloes with a model for ejecta thickness shows that these rock-poor layers are detected by 70-cm radar where they are on the order of 10 m and thicker. A SAR in orbit about Mars could use similar deep probing to reveal the nature of crater - and basin-related deposits.
Unusual Radar Backscatter along the Northern Rim of Imbrium Basin
A viewgraph presentation of the unusual radar backscatter properties along the Northern Rim of Imbrium Basin is shown. The contents include: 1) Visual and Infrared Observations of Moon; 2) Radar Observations of Moon; 3) Lunar Orbiter Photographs Geologic Setting; 4) 70-cm Radar Data; 5) .70-cm Radar Dark Halo Craters; 6) 3.8-cm Radar Data; 7) 7.5-m Radar Data; 8) 70cm, 3.8 cm and 7.5-m Radar Data; 9) Optical and Infrared Data; 10) Plato Rilles; 11) Isopachs of Crater Ejecta; 12) Plato-like Craters; 13) Observation Summary; 14) Interpretation Matrix; 15) Dark Halo Diameters vs. Crater Size; and 16) Radar Geologic Column.
The Mars Express - NASA Project at JPL
This viewgraph presentation gives a general overview of the Mars Express NASA Project at JPL. The contents include: 1) Mars Express/NASA Project Overview; 2) Experiment-Investigator Matrix; 3) Mars Express Support of NASA's Mars Exploration Objectives; 4) U.S./NASA Support of Mars Express; 5) Mars Express Schedule (2003-2007); 6) Mars Express Data Rates; 7) MARSIS Overview Results; 8) MARSIS with Antennas Deployed; 9) MARSIS Science Objectives; 10) Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) Experiment Overview; 11) Mars Express Orbit Evolution; 12) MARSIS Science - Subsurface Sounding; 13) MARSIS-North Polar Ice Cap; 14) MARSIS Data-Buried Basin; 15) MARSIS over a Crater Basin; 16) MARSIS-Buried Basin; 17) Ionogram - Orbit 2032 (example from Science paper); 18) Ionogram-Orbit 2018 (example from Science paper); and 19) Recent MARSIS Results ESA Press Releases.
Mars Express Science Overview
This viewgraph presentation provides a brief and more detailed overview of the Mars Express Science mission as well as results from the Mars Express instruments and the High Resolution Camera.
Unusual Radar Backscatter Properties Along the Northern Rim of Imbrium Basin
Earth-based radar backscatter from the lunar terrae is 2-4 times that of the maria. The largest (most conspicuous) exception is the terra along the northern rim of Imbrium Basin, where highlands that surround Sinus Iridium and crater Pluto have long wavelength (70-cm) radar backscatter that is comparable to (and sometimes weaker) the mare.
The Mars Express/NASA Project at JPL
An overview of the Mars Express/NASA Project at JPL is presented. The topics include: 1) Mars Express Mission Experiments and Investigators; 2) Mars Advanced Radar for Subsurface and Ionospheric Soundig (MARSIS) Overview; 3) MARSIS Experiment Overview; 4) Interoperability Concept; 5) Mars Express Science Operations; 6) Mars Express Schedule (2003-2007);
The NASA/JPl Aircraft Topographic Synthetic Aperture Radar (TOPSAR)
A description is provided of an aircraft radar interferometer, TOPSAR for.
Radar Studies of the Lunar Regolith
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Long-wavelength Radar Studies of the Lunar Maria
Radar measurements at 70 cm and 7.5 m wavelengths provide insight into the structure and chemical properties of the upper 5-100 m of the lunar regolith and crust. Past work has identified a number of anomalous regions and changes in echo strength, some attributed to differences in titanium content. There has been little opportunity, however, to compare calibrated long-wavelength backscatter among different units or to theoretical model results. We combine recent high-resolution (3-5 km) 70-cm radar data for the nearside with earlier calibrated full-disk observations to provide a reasonable estimate of the true lunar backscatter coefficient. These data are tested against models for quasi-specular scattering from the surface, echoes from a buried substrate, and Mie scattering from surface and buried rocks. We find that 70 cm echoes likely arise from Mie scattering by distributed rocks within the soil, consistent with earlier hypotheses. Returns from a buried substrate would provide a plausible fit to the observations only if the regolith depth were ~3 m or less and varied little across the maria. Depolarized echoes are due to some combination of single and multiple scattering events, but it appears that single scattering alone could account for the observed echo power, based on comparisons with terrestrial rocky surfaces. Backscatter strength from the regolith is most strongly affected by the loss tangent, whose variation with mineral content is still poorly defined. We compared the backscatter values for the mare deposits to the oxide contents inferred from spectral ratio methods, and found that in general the unit boundaries evident in radar images closely follow those seen in color difference images. The 70-cm data are not well correlated with TiO2 values found using the Charette relationship nor with Fe abundances derived from Clementine observations. The lack of a relationship between radar echo and Fe content is reasonable given the distribution of iron among various mineral phases, but ilmenite content (FeTiO3) has typically been cited as the dominant cause of changes in loss tangent (and thus the radar absorption). The lack of correlation between the radar data and TiO2 estimates may arise from uncertainties in the Charette technique, subtle differences in the upper surface and bulk properties of the regolith, mineralogic effects on the radar not linked to titanium content, or to some combination of these factors. Dark crater haloes in the mare and highlands, and low radar returns from apparent cryptomare regions, are used to illustrate the role radar data can play in identifying changes in regolith composition; low-return haloes around craters such as Petavius may indicate 5-25% contamination of the highlands soil by excavated mare material or a layer of rock-poor ejecta at least several meters deep. The 7.5-m data were shown to correlate to a reasonable degree with estimates of Fe abundance, suggesting that this component of the mare basalts is primarily responsible for attenuation losses at very long wavelengths. The different sensitivities of the two radar wavelengths and multispectral data offers the potential for future deep mapping of the mare lava flows and regolith.
Long-wavelength Radar Studies of the Lunar Maria
Radar measurements at 70 cm and 7.5 m wavelengths provide insight into the structure and chemical properties of the upper 5-100 m of the lunar regolith and crust. Past work has identified a number of anomalous regions and changes in echo strength, some attributed to differences in titanium content. There has been little opportunity, however, to compare calibrated long-wavelength backscatter among different units or to theoretical model results. We combine recent high-resolution (3-5 km) 70-cm radar data for the nearside with earlier calibrated full-disk observations to provide a reasonable estimate of the true lunar backscatter coefficient. These data are tested against models for quasi-specular scattering from the surface, echoes from a buried substrate, and Mie scattering from surface and buried rocks. We find that 70 cm echoes likely arise from Mie scattering by distributed rocks within the soil, consistent with earlier hypotheses. Returns from a buried substrate would provide a plausible fit to the observations only if the regolith depth were approx.3 m or less and varied little across the maria. Depolarized echoes are due to some combination of single and multiple scattering events, but it appears that single scattering alone could account for the observed echo power, based on comparisons with terrestrial rocky surfaces. Backscatter strength from the regolith is most strongly affected by the loss tangent, whose variation with mineral content is still poorly defined. We compared the backscatter values for the mare deposits to the oxide contents inferred from spectral ratio methods, and found that in general the unit boundaries evident in radar images closely follow those seen in color difference images. The 70-cm data are not well correlated with TiO2 values found using the Charette relationship nor with Fe abundances derived from Clementine observations. The lack of a relationship between radar echo and Fe content is reasonable given the distribution of iron among various mineral phases, but ilmenite content (FeTiO3) has typically been cited as the dominant cause of changes in loss tangent (and thus the radar absorption). The lack of correlation between the radar data and TiO2 estimates may arise from uncertainties in the Charette technique, subtle differences in the upper surface and bulk properties of the regolith, mineralogic effects on the radar not linked to titanium content, or to some combination of these factors. Dark crater haloes in the mare and highlands, and low radar returns from apparent cryptomare regions, are used to illustrate the role radar data can play in identifying changes in regolith composition; low-return haloes around craters such as Petavius may indicate 5-25% contamination of the highlands soil by excavated mare material or a layer of rock-poor ejecta at least several meters deep. The 7.5-m data were shown to correlate to a reasonable degree with estimates of Fe abundance, suggesting that this component of the mare basalts is primarily responsible for attenuation losses at very long wavelengths. The different sensitivities of the two radar wavelengths and multispectral data offers the potential for future deep mapping of the mare lava flows and regolith.
Magellan Final Science Reports
This volume is a brief summary of the scientific results of the Magellan Venus mapping mission as reported by the Magellan science investigators. Magellan has exceeded all of its mission objectives by obtaining high resolution radar images, surface elevation, and radiometry for more than 98% of the planet. The amount of stereo data gathered on Venus is more than that available for any other planet. Magellan's fourth cycle collected gravity data from an elliptical orbit to provide information on the relationships between surface features and the interior of the planet. With the successful completion of the aerobraking experiment, the spacecraft, in its lower orbit around Venus, has captured high resolution gravity near the poles from the nearly circular orbit. Every attempt has been made to provide useful documentation for the complete Magellan data set. Magellan data have been released to the public through the Planetary Data System (PDS) and the National Space Science Data Center (NSSDC) in photographs, lithos, brochures, digital form, and compact discs. With the release of Magellan data on the compact disc read-only-memory (CD-ROM) a revolutionary new way of doing science has resulted. This technology provides a way to store, distribute and access large volumes of data. The Magellan science investigators have utilized this wealth of data to provide answers to questions we have been asking for a long time. I would like to personally thank everyone on the Magellan team for the success of this important mission, a mission that has revealed information that will help us to better understand our own Planet Earth.