報告書番号

V06012

タイトル（和文）

DBF海洋レーダの表層流速自動推定法の開発

タイトル（英文）

Development of Automatic Estimation method for Surface Currents from Doppler Spectrum Obtained with Ocean DBF Radar

概要 （図表や脚注は「報告書全文」に掲載しております）

電中研では，沿岸流速観測のためのDBF技術を利用したVHFレーダの開発を行っている．
このレーダではVHF帯の電波を送信し，海面における後方散乱波を受信している．流速の推定では，受信波のスペクトルからブラック散乱波の明瞭なピーク周波数を検出し，このピーク周波数の表層流によるドップラーシフトを変換して計算している．
本レーダを用いた表層流動観測（遠隔流況モニタリング）を準リアルタイムで実施するには，レーダで記録したドップラースペクトルから流速を自動推定する必要がある．そのため，本研究では，ドップラースペクトルから自動的に流速を検出する手法を提案し，本手法の精度および限界について検証を実施した．本手法は，まず，ピーク周波数がレンジ方向に連続的であると仮定して，ドップラースペクトルにおけるブラッグ散乱波によるピーク周辺領域を抽出した．そして，この領域を通過域とするフィルタをドップラースペクトルに適用し，濾過されたスペクトルにモーメント法を適用してピーク周波数を検出し，視線方向の流速を算出した．本手法で推定された流速結果は手動ピークサーチした結果，およびADCPで観測した表層流速結果とよい一致を示した．
この手法の処理時間は40秒と短く，遠隔流況モニタリングに適用可能であることを示した．

概要 （英文）

CRIEPI has been developing 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 each range and azimuth cell are estimated by identifying the well-defined peak frequencies of backscattered signal by the Bragg scattering effect in the Doppler spectrum and then displacing from Doppler-shifted frequencies caused by ocean surface currents to according the phase speed of the sea surface wave.
The automatic estimation method for surface currents from the sea echo Doppler spectrum, which are received by radar system, is required to produce current velocities in the near real-time with the DBF Coastal Current Radar (DBF-CCR).
This study develops a method automatically identifying peak frequencies in the sea echo Doppler spectrum, and then evaluates the accuracy and limitation of this method.
This method firstly extracts the spectral region in ranges and frequencies around the peak frequencies, which are assumed to be continuous in ranges, from received spectrum by the adjacency matrix, and secondly identifies the peak frequencies by calculating the center frequencies in spectrum with the moments and sums of spectrum along the frequencies at any ranges within the extracted spectral area.
This method is evaluated by two comparisons: the first comparison between the surface current measurements calculated with this method and the shallowest currents with acoustic Doppler current profiler (ADCP), the second comparison between the surface velocities with this method and the surface velocities obtained from manual identifying peak frequencies.
The fist comparison results in the high correlations greater than 97% and the low standard deviations of residuals ranging from 9cm/s to 12cm/s.
The second comparison shows that the two residual currents and two M2 tidal currents are similar distributions in spatial, although the range of current estimates with this method is about 3km shorter than that with manual peak identifying method.
The processing time of this method is about 40 seconds short enough to procedure current estimates in the real-time with DBF-CCR.

報告者

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