Study of current fluctuations based on satellite altimetry data

利用星载雷达高度计测量海面高度是一种很有发展前途的技术；它几乎覆盖了世界上所有的海洋，没有由于云层的存在而造成的数据损失，并且可以直接从海表动力地形（这里简称SSDT）估计海面速度，这可以从测高数据中得到。然而，卫星轨道高度的估计误差太大，目前还不能用于地球物理研究。在本研究中，我们开发了一种程序，利用最优插值技术，利用最新的大地水准面数据估计SSDT的时间平均值和波动，并将结果与常规海洋观测结果进行比较。我们选择北太平洋西部的研究区域，使用1978年7 - 10月的卫星SEASAT测高数据。1988年，我们开发了对高程资料的分析程序，并估计了时间平均SSDT。相对于大地水准面估计的平均高程场定性地表明黑潮在有限的局部区域存在。但对于整个研究区，它不能用来估计平均SSDT（大地水准面数据精度不理想）。1989年，我们估计了SSDT的时间波动，并将结果与观测到的黑潮轴波动、东北海域冷暖水团运动和日本周围岛屿站的海平面波动进行了比较。结果表明，利用卫星测高资料估算的SSDT的时间波动能很好地反映海平面的长期实际波动。

Measuring sea-surface height by the radar altimeter on board satellite is a very promising technique; it covers almost all the world oceans, there are no data loss due to the presence of clouds, and surface velocities can be estimated directly from the sea-surface dynamic topography (here abbreviated SSDT) which could be derived from the altimetry data. However, the error of the estimated satellite orbit height is too large, so far, to use the data in geophysical studies. In the present study, we develop a procedure to reduce this error by using optimal interpolation technique, estimate the temporal mean and fluctuation of the SSDT using the latest geoid data, and compare the results with those from the conventional oceanographic observations. We select the study area in the western North Pacific, and use the altimetry data by satellite SEASAT for about three months (July-October, 1978).In 1988, we developed the analysis procedure for the altimetry data, and estimated the temporal mean SSDT. The estimated mean elevation field relative to the geoid qualitatively shows the existence of the Kuroshio in a limited local area. But for the whole of the study area, it can not be used to estimate the mean SSDT (the accuracy of the geoid data is not satisfactory).In 1989, we estimated the temporal fluctuation SSDT, and compared the results with observed fluctuations of the Kuroshio axis, movements of the warm and cold water masses off Tohoku, and sea level fluctuations at island stations around Japan. The results show that the temporal fluctuation of the SSDT estimated from the satellite altimetry data represents the actual long-term fluctuations of the sea level very well.