報告書番号

V15002

タイトル（和文）

DBF海洋レーダの表層流速推定法の改良

タイトル（英文）

Improvement of Estimation Method for Surface Currents from Doppler Spectrum Obtained with DBF Ocean Radar

概要 （図表や脚注は「報告書全文」に掲載しております）

当所で開発したVHF帯のDBFレーダで観測したスペクトルから自動的に視線流速を推定するシステムの改良を行った．前回のモデルでは，視線流速付近の情報を持つ一次成分近傍を抽出するフィルタを作成していたが，このフィルタでは，流速方向に幅が広く，波浪の情報を持つ二次成分を含んでいたため，視線流速に両成分が混在するスペクトルが通過していた．そのため，本研究では，フィルタの幅を見直す改良を行い，幅について最適な値を，レーダ観測と同時に行ったADCP観測結果の比較により推定した．ADCP観測結果との比較で，最小の誤差および最大の相関をもつフィルタの幅は４０cm/s程度と推定された．

概要 （英文）

CRIEPI developed Very high-frequency (VHF) radars with a digital beam-forming system (DBF-radars system) for current measurements. Radar system observes Doppler spectrum of sea echo by transmitting and receiving VHF radio waves. The coastal currents within a cell in range and azimuth are estimated by identifying the well-defined peak frequencies of the first-order scattering from backscattered signal and then displacing from Doppler-shifted frequencies caused by ocean surface currents to according the phase speed of the sea surface wave. In order to produce current velocities in the near real-time with the DBF Coastal Current Radar (DBF-CCR), CRIEPI developed the automatic estimation method for surface currents from the Doppler spectrum. However, the method needs to prevent the estimation of the first-order scattering frequency from the contamination of the second-order scattering, which lie beside the peak frequencies of first-order scattering, effected by sea waves, recently.
In order to prevent the contamination, the band width of the filter extracting the first-order scattering is reformed in this study. The band width is optimized to be 40 cm s$^{-1}$, that of the previous method 100cm s$^{-1}$, from the comparison of the currents by the method with that by acoustic Doppler current profiler (ADCP). As a result, the improved method with the band width of 40 cm s$^{-1}$ shows the better agreement with mannual detected currents: better correlation and smaller RMSE between the currents estimated by the method and currents manually detected .

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