Development of software for determination of the lunar topography using the laser altimeter and optimization of measurements

在SELENE任务中使用激光高度计测量月球地形，需要精确确定激光系统与月球中心的对准，并在精确确定航天器轨道的同时，对各种系统误差进行改正。在本研究中，我们对测量仪器进行了重新研究和优化，并开发了解决上述问题的软件，取得了以下结果：1)考虑到月球表面地形的分布，优化了激光发射机的功率，并可以在较强的太阳辐射和月球表面辐射的情况下优化仪器的设计。本研究完成了高度计的实验模型，并对高度计进行了热测试和振动测试。热测试已通过，没有任何问题。然而，在光学系统的机械支撑件上发现了一个小裂纹，我们改进了仪器以加强支撑件(Kawano等人，1998，纳米基等人，2000)。2)我们通过比较激光高度计数据和立体相机的数据，建立了解决激光高度计中高度和时间信号误差的方法(Kawano等人，1999，Araki等人，2000)。3)我们可以通过对激光高度计数据进行交叉分析来开发提高航天器轨道确定精度的方法。然后，建立了一种利用轨道飞行器和中继卫星的VLBI和多普勒观测数据来确定轨道的新方法(Heki等人，1999年，MatSumoto，Heki等人，1999年)。对月球潮汐对航天器轨道的影响进行了数值估算。所获得的结果表明，我们很有可能通过观测航天器的轨道运动来确定月球潮汐参数(OOE和MatSumoto，提交给J.G.S.J.，Abe和Ooe，2001年出版)。

The measurement of lunar topography by using a laser altimeter in SELENE mission does require precise determination of alignment of laser system to the lunar center and correction for various systematic errors togeter with making precise determination of the orbit of spacecraft. We, in this study, reinvestigated the instrumentation and optimized the measurement, and developed software to overcome the above problems obtaining the following results.1) We optimized the power of the laser transmitter considering the distribution of topography on the lunar surface and also could optimize the design of instrument for thermal condition with the rather strong solar radiation and the radiation from the lunar surface. An experimental model of the altimeter was completed in this study and we achieved thermal and vibration tests with it. The thermal test was cleared with no problems. It, however, was found a small crack in a mechanical support for the optical system and we improved the instrument to strengthen the support (Kawano et al., 1998, Namiki et al., 2000).2) We established methods for solving the errors of altitude and signal of time in the laser altimetry by means of comparing the laser altimeter data and these of the stereo camera etc. (Kawano et al., 1999, Araki et al., 2000).3) We could develop methods for improving the precision of orbital determination of the spacecraft by employing the Crossover analysis of the laser altimeter data. Then a new method was established for determination of the orbit by using both the VLBI and the Doppler observation data of the orbiter and relay satellite (Heki, et al., 1999, Matsumoto, Heki et at., 1999). The lunar tidal effect on the orbit of the spacecraft was numerically estimated. The obtained results suggest us a high possibility to determine lunar tidal parameters by observations of orbital motion of the spacecraft (Ooe and Matsumoto, submitted to J.G.S.J., Abe and Ooe, 2001, in press).