Lunar surface reflectance by LALT aboard KAGUYA

Details Lunar surface reflectance by LALT aboard KAGUYA Lunar surface reflectance by LALT aboard KAGUYA

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23c1283n&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P23C-1283

Physics

[5462] Planetary Sciences: Solid Surface Planets / Polar Regions

Scientific paper

The Laser Altimeter (LALT) aboard Japanese lunar explorer KAGUYA (SELENE) is a ranging instrument which measures the distance between the satellite and the lunar surface with accuracy of 1 m by detecting the timing delay of the reflected laser light. The main science goal of the LALT is to obtain the lunar global topographic data including polar regions for the study of the origin and the evolution of the Moon [1]. Besides, the LALT is equipped with an intensity monitor of the returned pulses. The intensity of the returned pulses contains information concerning surface roughness and reflectance of the footprints, which will contribute to the study of the lunar surface maturity and age. The reflectance at LALT wavelength (1064nm) is sensitive to the surface maturity and composition. The data should be particularly important at lunar polar regions where camera instruments should suffer from phase angle effects in the surface reflectance and moreover cannot obtain reflectance data at the permanently shadowed area. The normal operation of the LALT began on 30th, December 2007 after two months’ commissioning phase. Before the end of the normal operation phase in October 2008, the LALT measured more than 10 million range data. Unfortunately, due to the laser power decrease and also possible smaller surface reflectance than the expected value before launch (15 % at 1 micro meter), the return pulse intensity during the nominal mission phase is so small that they are not reliable enough to discuss the surface property. During the extended mission phase, which started November 2008, the satellite altitude decreased to 50 km. Due to the malfunction of the reaction wheel and high-voltage instruments were shutdown, the observation was suspended until 11th of February, 2009. LALT successfully resumed observation on 12th February and continued observation until the controlled crash of KAGUYA onto the Moon on 10th of June, 2009. Thanks to the lower orbit during this phase, the return pulse intensity is high enough to be used for the study of the surface property. Especially, it is of interest whether water ice exists or not on the bottom of the eternal shaded regions in the polar region. If we assume that the surface roughness within the size of the footprint is the same inside and the vicinity of a crater, the change of the intensity is due to the variety of the reflectance. It can be used for possible detection of the water ice if exists. We will report the initial results of the analysis of derived reflectance, especially of the lunar polar regions. references [1] H. Araki et. al., Science, 323, 897-900 (2009).

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