人工衛星「まいど1号」で取得した電磁波形に対する考察

摘要

「まいど1号」は，宇宙航空研究開発機構（JAXA）からμ-LabSat の技術移転を受け，東大阪を中心とする中小企業群が製造し，2009年1月23日に打上げられた質量57kg，サイズは一辺が50cmの立方体を包絡線とする八角柱の小型人工衛星である（1）（2）（図1参照）。これには，筆者らのグループが開発した，雷放電に伴うVHF帯広帯域電磁波を受信・記録するVHF帯広帯域波形測定装置を搭載している。衛星本体および搭載機器は，μ-LabSatにおける実績晶と民生品を多用することで省コストおよび短開発期間を実現し，試験によりその信頼性を確保する手法で完成させている。%A small satellite "Maido-1" had been launched on January 23, 2009 and injected into the sun-synchronous polar orbit at an altitude of 660km. Broadband Measurements of Waveform for VHF Lightning Impulses (VHF sensor) is onboard to examine the feasibility of the space-borne VHF broadband digital interferometer recording VHF lightning impulses in space. 158 sets of VHF sensor observations had been conducted around the world and about 15,000 waveforms were recorded. The major achievements of VHF sensor on "Maido-1" satellite are; to verify VHF sensor developed based on ground-based equipments with commercial-off-the-shelf products, to validate the design of the sensitivity based on the numerical study of EM propagation through the ionosphere, and to confirm the noise environment in the orbit is available to the VHF broadband EM observations for lightning. This paper represents the study on the received EM waveforms focusing on their regional variation, pulse widths, pulse pairs and so on. These characteristics are dovetailed with the numerical simulation for the ionospheric propagations and are accountable by the described model.