Thermal infrared (TIR) data, acquired by instruments on several NASA satellite platforms, are primarily used to estimate the surface temperature/emissivity of the Earth's land surface. One such instrument launched on NASA's Terra satellite in 1999 is the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which has a spatial resolution of 90 m. Using ASTER data, NASA/Jet Propulsion Laboratory recently released the most detailed emissivity map of the Earth termed the ASTER Global Emissivity Dataset (ASTER GED) that was acquired by processing millions of cloud free ASTER scenes from 2000 to 2008. The ASTER GEDv3 provides an average emissivity at ~100 m and ~1 km, while GEDv4 provides a monthly emissivity from 2000 to 2015 at ~5 km spatial resolution in the wavelength range between 8 and 12 µm. Validation with lab spectra from four desert sites resulted in an average absolute band error of ~1%, compared to current heritage MODIS products that had average absolute errors of 2.4% (Collection 4) and 4.6% (Collection 5).
Multispectral thermal infrared remote sensing of Hawaiian basalts younger than a few hundred years old can be used to discriminate basalt lava flows that are difficult to map with visible and near‐infrared images. Laboratory thermal infrared reflectance spectra of the exposed surfaces of Mauna Loa and Kilauea basalts show systematic changes with age. Fresh glass collected from active lava flows shows a broad reflectance feature between 8 and 12 μm, indicative of a strong degree of disorder. After a few weeks of exposure to the environment the spectra of the top surfaces of samples begin to exhibit spectral features suggestive of ordering into silicate chainlike and sheetlike units. With progressive aging, features of apparent sheetlike structures become the preferred mode. As soon as 3 years after emplacement, a silica‐rich coating can begin to develop on the surfaces, adding another spectral feature to the laboratory reflectance measurements. The Thermal Infrared Multispectral Scanner (TIMS) with six channels between 8 and 12 μm has been used to take advantage of these spectral differences in basalts to map flows in Hawaii. Remote sensing instruments with increased spectral resolution in the thermal infrared would aid in further discrimination of basalts with more subtle differences in age, quenching, and weathering histories.
Data from the lunar‐orbiting Apollo 17 radar sounding experiment (60‐m wavelength) have been examined in both digital and holographic formats. Surface backscatter (clutter) which masks possible radar returns originating from subsurface changes in lunar electrical properties was reduced by simultaneously comparing radar data from two orbits. Radar returns that correlate from orbit to orbit form two distinct alignments in Mare Serenitatis and one in Mare Crisium. It is proposed that these alignments represent subsurface reflecting horizons. The hypothesis is tested by showing that (1) most of the radar returns fall outside the ambiguity region of the correlation technique, (2) the results are consistent between optically and digitally processed data, (3) the signal levels of the proposed subsurface features are well above the noise floor, (4) the inferred loss tangents appear to be consistent with returned sample measurements, and (5) the discontinuous nature of the reflections most likely arises from interference effects. It is concluded that there are two subsurface radar reflectors with mean apparent depths of 0.9 km and 1.6 km below the surface in Mare Serenitatis and one reflector at a mean depth of 1.4 km below the surface in Mare Crisium. These reflectors represent basin‐wide subsurface interfaces.
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