Statistics – Applications
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13d1707r&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P13D-1707
Statistics
Applications
[5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
The Lunar Orbiter Laser Altimeter (LOLA) is a laser (1064 nm) ranging instrument in lunar orbit. In addition to determining topography, LOLA was designed to measure the pulse energy returning from the Moon. The ratio of returned/transmitted pulse energy is a measure of surface reflectance at precisely 0° phase angle (angle between source, target and observer). Previous imaging data must contend with highly variable lighting, potentially introducing systematic errors due to uncertainty in lunar photometric properties. As an active sensor, LOLA provides measurements with uniform illumination geometry, which allows for precise comparison of the reflectance of different lunar terrains. This is the first lunar reflectance dataset at a single common viewing and illumination geometry, providing a unique new view of the reflectance of the Moon. We present a global reflectance image of the Moon at 4 pixels per degree (~8 km) resolution. LOLA lacks a source of known brightness in flight so the absolute calibration of the return pulse energy has relied on pre-launch testing. We refined this calibration by comparing and correcting LOLA reflectance to Kaguya Multiband Imager and Chandrayaan-1 M3 spectrometer data at similar wavelengths obtained at 0° phase angle. The specific quantity measured is the normal albedo, the radiance of a surface relative to a Lambertian surface illuminated normally and this quantity ranges from 0.1 to 0.5, much higher than reflectance at other geometries. This dataset is particularly useful for studying the lunar poles. At high latitudes, topographic shading dominates the radiances measured by traditional passive sensors. LOLA measurements are free of variations in apparent reflectance due to topographic shading and can be uniquely used to compare the reflectance of the polar and equatorial regions of the Moon. This allows assessment of general composition (reflectance is dominantly controlled by iron content) as well as the presence and distribution of pyroclastics, small mare deposits and cryptomaria. Early results from this unique new data set show there are no exposures of cryptomare or pyroclastic deposits in the south polar region, as previously proposed. The north polar region also lacks such exposures. The albedo anomaly associated with the South Pole-Aitken basin interior, that may represent the melt sheet, does not extend to the south pole, but remains within the proposed inner ring of the basin. Additional potential applications include: precise calibration of earth-based measurements of terrestrial albedo that depend on measurements of the reflectance of the Moon in earthlight; tests of spatially resolved estimates of general lunar photometric properties; and validation or support of other data sets that include latitude-dependent normalizations, particularly in the poorly characterized polar regions.
Lucey Paul G.
Mazarico Erwan
Neumann Gregory A.
Riner Miriam A.
Smith Douglas E.
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