Lunar Laser Ranging(LLR) is an challenging experiment which relates to many fields such as optics,mechanism and electronics. The returned photon numbers are few in LLR because of the long distance from earth to moon and the efect by atmosphere. Adaptive optics is considered to be used in LLR to compensate the laser beam "jitter" and laser beam shape distortion caused by atmosphere, so that the returned photon numbers will be increased. In order to test the algorithms used for low contrast extended lunar surface, Data of lunar surface near APOLLO 11 and APOLLO 15 were collected. Ab- solute diference algorithm and cross-correlation algorithm are used to compute the wavefront tip-tilt errors. Long exposure images with and without removing the tip-tilt errors are compared to test the efect of the two algorithms. Results reveal the algorithms work well. Field rotation Based on the 1.2m Alt-Az telescope of Yunnan observatory is computed in diference conditions. It shows that field rotation shouldn't be ignored in LLR. In order to compensate the efect of the ¯eld rotation, The reference image should be changed in a short time or the detector should be rotated in the same velocity and the same direction. According to the laser beam characters and the performance of the 61 element adaptive optics system, the returned photon numbers are analyzed when 61 element adaptive optics system is used in LLR. Results show the returned photon numbers will be increased obviously.
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