Overview of the Waveform Capture in the Lunar Radar Sounder on board KAGUYA

The Lunar explorer "gKAGUYA"h (SELENE) spacecraft will be launched on September 13, 2007. The Lunar Radar Sounder (LRS) is one of the scientific instruments on board KAGUYA. It consists of three subsystems: the sounder observation (SDR), the natural plasma wave receiver (NPW), and the waveform capture (WFC). The WFC is a high-performance and multifunctional software receiver in which most functions are realized by the onboard software implemented in a digital signal processor (DSP). The WFC consists of a fast-sweep frequency analyzer (WFC-H) covering the frequency range from 1 kHz to 1 MHz and a waveform receiver (WFC-L) in the frequency range from 10 Hz to 100 kHz. The amount of raw data from the plasma wave instrument is huge because the scientific objectives require the covering of a wide frequency range with high time and frequency resolution; furthermore, a variety of operation modes are needed to meet these scientific objectives. In addition, new techniques such as digital filtering, automatic filter selection, and data compression are implemented for data processing of the WFC-L to extract the important data adequately under the severe restriction of total amount of telemetry data. Because of the flexibility of the instruments, various kinds of observation modes can be achieved, and we expect the WFC to generate many interesting data. By taking advantage of a moon orbiter, the WFC is expected to measure plasma waves and radio emissions that are generated around the moon and/or that originated from the sun and from the earth and other planets. One of the phenomena of most interest to be obtained from the WFC data is the dynamics of lunar wake as a result of solar wind-moon interaction. Another scientific topic in the field of lunar plasma physics concerns the minimagnetosphere caused by the magnetic anomaly of the moon. There are various kinds of other plasma waves to be observed from the moon such as Auroral Kilometric Radiation, electrostatic solitary wave, fp and 2fp emissions, and solar radio emissions. The first data from the WFC will be obtained in the beginning of November, 2007. In the presentation, we introduce an overview of the WFC onboard KAGUYA as well as the initial results obtained by the receiver.