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

在利用激光高度计测量月球表面地形的SELENE使命中，需要精确确定激光系统对月心的对准度，并对各种系统误差进行修正，同时还要精确确定航天器的轨道。本文针对上述问题，对仪器进行了重新研究和优化，并开发了相应的软件，取得了以下成果：1）根据月表地形分布情况对激光发射器的功率进行了优化，并针对太阳辐射和月表辐射较强的热环境对仪器进行了优化设计。本研究完成了高度表的实验模型，并进行了热态和振动测试，热态测试没有问题。然而，在光学系统的机械支撑中发现了小裂纹，并且我们改进了仪器以加强支撑（Kawano等人，1998年，Namiki等人，2000）。2）通过比较激光高度计数据和立体相机等的数据，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，1999年，Araki等人，（3）利用激光高度计数据的交叉分析，可以发展提高航天器定轨精度的方法。然后建立了一种利用轨道器和中继卫星的VLBI和多普勒观测数据进行定轨的新方法（Heki，et al.，1999，松本，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和松本，提交给J.G.S.J.，Abe和Ooe，2001年，出版中）。

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).