研究成果　研究報告書（電力中央研究所報告）詳細情報　電力中央研究所

電力中央研究所　研究報告書（電力中央研究所報告）

概要（和文）: 本研究では，有明海での観測結果を用いて，海洋レーダ観測における塩分の影響について検討を行った．観測は送信周波数41.9MHzのDBF海洋レーダを用いて行い，2007年7月における筑後川の大出水時の観測データ対象に解析を行った．海洋レーダ観測における1次散乱強度の最大値（以後，受信電力）と水深1m地点で計測された塩分，および風速について比較を行った結果，計測された塩分と海洋レーダの受信電力はほぼ同期した変動を示し，塩分の低下とともに受信電力が低下する傾向が見られた．さらに受信電力の低下箇所の分布を算出した結果，受信電力の低下箇所は表層流と同じ方向へと伝搬していく傾向があり，また，その低下箇所は既往の研究で指摘されている筑後川から放流される河川水の流出経路とよく対応していた．さらに，受信電力と風速との相関や，受信電力の距離減衰の傾向を調べた結果，受信電力の低下は伝搬損失の増加だけでなく，散乱断面積の減少も影響している事が示された．

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タイトル（英文）: The effect of surface salinity on the observation using the Ocean Radar

概要（英文）: The effect of sea surface salinity on the observation using Ocean Radar with 41.9 MHz radio wave has been investigated through the field observation in Ariake Bay. The receiving signal intensities defined as the maximum value of first order Doppler scattering in Doppler spectrum were compared with in situ measurement of sea surface salinity at 1 m depth and wind velocity. The results show that temporal variation of receiving signal intensity agrees well with that of sea surface salinity. The receiving signal intensity also shows the high attenuation under low sea surface salinity condition. This result consists with the theory of attenuation of radio wave propagating with ground wave mode. Furthermore, authors investigated the temporal variations of horizontal distribution of receiving signal intensity just after large flood from Chikugo River. The areas of lower receiving signal intensity spread to parallel direction with surface current, and agreed closely with the river flow area described in past studies. The decreases in receiving signal intensity sometimes occur without decease in wind speed. Moreover, the receiving signal intensity increases beyond the area of lower signal intensity. These results suggest that the decrease in the receiving signal intensity by the effect of surface salinity was caused not only by the high attenuation in radio wave propagation but also by the decrease of scattering cross section.