密度の鉛直分布をEOF解析し，その第1－3モードの振幅と,lOOOdbar面準拠の海面力学高度および 位置との間の経験式を求めることにより,黒潮周辺海域の密度の鉛直分布を海面力学高度から推定する方 法を提案した．3種の多重回帰モデル（位置の関数：1－3次式）と，力学高度のみ考慮する回帰モデル を比較した結果，多重回帰モデルの方が密度推定には有効であることが示されたが，3種の多重回帰モデ ル間の差は僅かであった．推定誤差(rms値）は,8月に最大(0.3 kg/m^3),2月に最小(0.15 kg/m^3)と なり，また，上層200mでは，その値･変動ともに大きく，それ以深では両者とも小さいことが示された． 黒潮を横断する1本の測線上で観測された密度分布と,推定された密度分布の両者より求めた地衡流速間 の差(rms値）は0.04 m/sであった．今回の結果より，密度の鉛直分布の海面高度からの推定の可能性が 示された．

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We have developed a multi-sensor, salinity/temperature measurement system based on the XCTD (Expendable Conductivity, Temperature & Depth Profiling System) and applied it to an observation well for a groundwater survey in a salt intrusion area. Five CT sensors made by modification of XCTD probes were connected by a cable, and the distances between sensors were adjustable. The cable was 50m long and connected at its end on the ground to a measurement control and data logging system consisting of a notebook computer and peripheral components. In addition, a pressure sensor for measuring fluctuation of water level in the well was included in the system. Observation experiment using this system was carried out in the observation well of the 50m depth in the embankment (about 8.7km upstream from the river mouth) of the River Gonokawa located in the western part of Shimane Prefecture, Japan. We obtained conductivity, salinity, temperature and water-level data every 5 minutes for about two months. By the long-term observation of salinity and water temperature by the CT sensors, it was clarified that the fresh-salt water interface in the groundwater was fluctuating with time. Furthermore, there was a correlation between fluctuation of the ground water level and water-level/flow rate of River Gonokawa.

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1980年代から広く普及してきた船舶搭載型ADCP(音響ドップラー流速計）は，音波を船底から斜め下 方の4方向に発射するタイプ（4ビーム型）が主流で，これを用いた流速計測の技術については数多くの 研究が行われている．一方我が国では，上記の4ビーム型に加えて，3方向に音波を発射するタイプ（3 ビーム型）も広く使用されているが，その計測技術について必ずしも十分な研究が行われているとは言え ない．両者は，測器としての原理は同様であるが，計測処理上の計算式等に違いがあることから，3ビー ム型の船舶搭載型ADCPについて，その計測技術を整理し，誤差要因とその実用的な更正手法について述 べる．

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Saline wedge invasion in the Gonokawa River was observed over lengthy periods in summer and winter in 1998. Here we discuss the observed hydrological data from an hydraulic analysis viewpoint. Saline wedge behavior was captured precisely using newly developed observation systems which measured salinity, temperature and identified the interface between fresh and salt water by sonic echo. According to these observations, the length of the saline wedge decreased when the river discharge increased. In other words, the saline wedge moved downstream as the fresh water velocity increased. This showed that the river comprised a two-layer laminar flow with a viscous interface. Wecalculated the length of the saline wedge using specific parameters including depth to the interface, temperature and salinity. The results accorded well with the observed data, and a formula to evaluate the interfacial resistance coefficient incorporating the Keulegan number was proposed. We have also measured the invasion speed of the saline wedge. Simulations were carried out to estimate the invasionspeed, but the results did not agree with the observed phenomena, because the simulation model assumed behavior as a perfect fluid.

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Seasonal variation of carbon of Bacteria, Synechococcus, ANF,HNF,Phyioplankton, and Zooplankton were investigated in Ise Bay, in 1995. In addition, estimated production rates of Bacteria, Synechococcus, phyioplankton, and grazing rates of HNF, zooplankton. Using these results, we approximate production rates of each food chain. In this place, we categorized lOum or less phytoplankton Bacteria Synechococcusand ANF as a producer of Microbial food chain, and cat egorized other producers as a producer of grazing food chain. Then, we compared and examined that interrelationship between each microorganism and environment factor. As a result of this research, water temperature and grazing pressure by HNF were important as change factor of Bacteria, and grazing pressure of HNF and Oikopleura were important as Synechococcus. The microbial food chain/grazing food chain production ratio was 0.66 on the whole, grazing food chain was more important, but microbial food chain was more important in September and December. On the other hand, dominant species of the zooplankton were Penilia avimstris (CLADOCERA), and Bivalve larva and Oithonadavisae (COPEPODA) when produc tion of Bacteria, Synechococcus, etc. was the highest in summer. P. avirostris and Bivalve larva are herbivorous pico- nano, nanoplankton feeder, and O.davisae is omnivorous nano-microplankton feeder. The grazing rates of these dominant species occupied 86% (in August, and the whole 67%) to the grazing rates of the whole zooplankton, and the seasonal variation was similar to change of production rates of Microbial food chain. These results suggest production of a Micro bial food chain links to production of zooplankton. On the other hand, zooplankton population and that species composition were seasonal changing so that food can be used effectively.

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