かぐや（SELENE）搭載レーザ高度計による観測

抄録

The Laser altimeter (LALT) is one of the 14 instruments boarded on KAGUYA lunar orbiter. The LALT emits a laser pulses every 1 s or 2 s from about 100 km altitude to the lunar surface and the round trip times of these pulses are converted to range data. The LALT incorporates Cr doped Nd:YAG laser whose pulse energy is 100 mJ and the beam divergence angle is 0.4 milli radian yielding the footprint diameter of 40 m. The aim of the LALT is to conduct precise and accurate measurements of the global topography of the Moon. The first laser ranging test of the LALT was carried out on 25 November, 2007 when the high voltage and laser transmit and receiving unit were turned on for the first time. The LALT has started nominal observations since 30 December, 2007 after the initial tuning of the avalanche photo diode (APD) detector in the receiving system. The LALT acquired more than 11 million range data by the end of November, 2008. Detailed descriptions of the measurement principle, the hardware design, structures, and several functions of the LALT are presented in the first half of this article; then followed by reviews of several tests and their results on the ground and in orbit.