共光路百赫兹激光测月系统主回波重叠的研究

Study on transmitting/echo signal overlapping in common-optical-path 100 Hz-rate LLR system

高重频激光测月技术是月球激光测距的一个重要发展趋势,对获得更多的激光测月数据具有重要意义。在之前的10 Hz测月频率基础上,中国科学院云南天文台开发了共光路百赫兹激光测月系统。然而在共光路系统中,存在发射激光光子的主波时刻与接收激光光子的回波时刻相重叠的现象,影响了对回波光子的探测。文中从信号时序角度对主回波重叠现象进行了分析,研究了光子飞行时间与重叠现象间的关联性。利用某天的月面反射器的轨道预报对系统的重叠发生比率进行了模拟,得出了当天观测时段内整体的重叠发生率约为8%。同时开展了基于每个发射时刻的分段模拟,结果与前者吻合。对微调转镜转速以避开主回波重叠的方法进行了分析,开展了对应的转镜转速调整试验,结果表明当重叠发生时,对转速进行适量调整可以避开主回波重叠。

In Lunar Laser Ranging(LLR),higher repetition rate is an important trend for development,which is also of great significance for acquiring more LLR data.Based on the previous 10 Hz ranging rate system,a 100 Hz lunar ranging system with common-optical-path structure was developed by Yunnan Observatories,CAS.However,overlapping of the transmitting/echo signals exists in such a common-optical-path system,and seriously disturbs echo-photon detection.In the paper,the overlapping phenomenon was analyzed from the perspective of time sequence,and the correlation between the overlapping and the Time of Flight(TOF)was studied.Overlapping in the system was simulated with the orbital prediction of a lunar retro-reflector of a certain day,and the general overlapping ratio was approximately 8%for the observational duration.Sectional simulation based on each transmitting epoch was also performed,its result was consistent with the previous one.The method of avoiding overlapping by slightly adjusting rotating-mirror’s speed was analyzed,and corresponding experiment was carried out,as proper speed adjustment turned out to be a solution when the overlapping happened.