STUDY OF PLANETARY MAGNETOSPHERES BY DEVELOPING SPACE-VEHICLE-BORNE FAST CORRELATION-SPECTROMETER

为了研究行星磁层与太阳风之间的相互作用，直接测量与能量转移有关的等离子体波活动是至关重要的。在未来的行星高层大气探测计划中，应该观察到宽频率的波和大规模的电场。在目前的项目中，我们开发了一种仪器，用于测量火星和木星等行星磁层以及行星际空间中产生的波的光谱。该装置的设计具有与航天器有效载荷条件相匹配的规格。(1)通过对EXOS-D卫星观测到的地球磁层数据的分析和对行星磁层的研究，发现在许多情况下，从直流到高频范围内的波是同时产生的。这一事实导致我们在频谱分析中将极低频成分与高频成分分离。对极低频分量采用多比特采样，便于遥测，对高频分量采用低比特相关法进行分析。(2)采用一比特校正方法较好地测量了平稳和准平稳信号的频谱；嘶嘶信号和呼啸大气已被很好地识别。(3)对其中一个信号进行多比特采样，与另一个信号进行1比特采样，通过互相关法估计波极化。因此，要存储或遥测的数据大大减少。(4)短持续时间信号（如脉冲）的绝对功率不能总是通过一比特相关来精确测量，这可能是低比特相关方法的一个弱点。(5)采用CODEC、差分PCM等数据压缩技术，遥测数据量减少30%以上。(6)建立了含直流分量的宽带观测电场传感器。结果表明，低比特相关方法是传统光谱和偏振分析技术的一种选择，适合航天器的小载荷条件。少

Direct measurements of plasma wave activities concerned with the energy transfer are essentially important in order to study the interaction between the planetary magnetosphere and the solar wind. Waves in wide frequencies and large-scale electric fields should be observed in the future exploration program of the planetary upper atmosphere. In this present project we have developed an apparatus to measure the spectra of the waves generated in the planetary magnetosphere such as Mars and Jupiter as well as in the interplanetary space. The apparatus is designed to have specification matched with the payload conditions of the spacecraft. We have made cleared the following points :(1) From data analysis of the earth s magnetosphere observed by the EXOS-D satellite and works on the planetary magnetospheres, the waves are found to be simultaneously generated in the range from DC to high frequency in many cases. This fact leads us to separate the extremely low-frequency components from high-f … More requency components in the spectral analysis. The extremely low-frequency components are sampled in multi-bits and the data can be easily telemetered while the high-frequency components are analysed by the low-bit correlation method.(2) Spectra of the stationary and quasi-stationary signals are well measured by the one-bit correction method ; hiss-type signals and whistling atmospherics are confirmed to be well identified.(3) Wave polarization is estimated by the cross-correlation method when one of the signal is multi-bit sampled and correlated with the other signal sampled by one-bit. Therefore the data to be stored or telemetered is much reduced.(4) The absolute power of the short-duration signal such as an impulse cannot always be accurately measured by the one-bit correlation This may be an weak point of the low-bit correlation method.(5) By means of the data compression techniques such as CODEC and Differential PCM, the number of data telemetered is reduced by more than 30 %.(6) The sensor of electric field for wide-band observation including DC component is established.From these results, we conclude that the low-bit correlation method is an option to the conventional spectral and polarization analysis technique matched with the small payload condition of the spacecraft. Less