Study of current fluctuations based on satellite altimetry data

用卫星上的雷达高度计测量海面高度是一种很有前途的技术;它几乎覆盖了世界上所有的海洋，不会因云层的存在而丢失数据，而且可以直接从海面动态地形（这里简称为SSDT）中估计海面速度，而海面动态地形可以从测高数据中得出。然而，迄今为止，卫星轨道高度的估计误差太大，不能用于地球物理研究。在本研究中，我们开发了一个程序，以减少这种错误，通过使用最佳插值技术，估计的时间平均值和波动的SSDT使用最新的大地水准面数据，并比较结果与传统的海洋观测。我们选取北太平洋西部的研究区域，利用1978年7 - 10月的SEASAT卫星测高资料，于1988年开发了测高资料的分析程序，估算了SSDT的时间平均值。相对于大地水准面的平均高程场的估计定性地表明了黑潮在有限的局部区域内的存在。1989年，我们估算了SSDT的时间涨落，并与黑潮轴的涨落、东北外海的冷暖水团的运动以及日本各岛站的海平面涨落作了比较。结果表明，由卫星测高资料估算的SSDT的时间变化很好地反映了海平面的长期变化。

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.