GPM（全球降水観測計画）/DPR（二周波降水レーダ）軌道上校正方法の検討

摘要

全球降水観測計画（GPM）は，レーダとマイクロ波放射計を搭載した主衛星とマイクロ波放射計を搭載した副衛星群のデータを組み合わせ，全地球の降水量を高精度に高時間・空間分解能で観測する計画である．主衛星は日米共同開発で，中心センサーの二周波降水レーダ（DPR）の闘魂は日本（JAXAとNICT）で実施している．二周波降水レーダは，熱帯降雨観測衛星（TRMM）搭載降雨レーダの成功を引き継ぎ，同じ形式の電子走査型レーダで二周波（Ku帯とKa帯）化し，高感度化と降水強度推定精度の向上を実現する．このDPRの軌道上での性能を評価するために実施する校正方法の検討状況と，外部校正実験に使用するレーダ校正器の開発状況を紹介する．%The Global Precipitation Measurement (GPM) project which is lead by Japan and the USA consists of CORE satellite which carries dual frequency precipitation radar (DPR) and microwave radiometer and constellation satellites which carry microwave radiometer. Japan side (JAXA and NICT) is responsible for the development of DPR and the basic concept of the DPR is to utilize the heritage established by the development of the precipitation radar onboard the Tropical Rainfall Measuring Mission (TRMM). In-flight calibration plan for the Dual-frequency Precipitation Radar (DPR) on the GPM (Global Precipitation Measurement) Core Observatory will be introduced. The DPR consists of a Ku-band precipitation radar (KuPR) and a Ka-band precipitation radar (KaPR). The KaPR can measure snow and light rain, and the KuPR can measure heavy and moderate rain. In an overlapped dynamic range in both KaPR and KuPR, drop size distribution (DSD) information and more accurate rainfall estimates will be provided by a dual-frequency algorithm, which utilize the differences in both rain attenuation and scattering from the matched beam data observed by KaPR and KuPR. The DPR has adjustment mechanisms which enable KaPR and KuPR beam directions to be aligned in the same direction. A DPR beam adjustments procedure on orbit will be proposed.