Possibility of current parameter retrieval from radar data

摘要

The possibility to retrieve parameters of a current from radar data is under investigation. The study is based on ERS SAR and TU-134 RAR images. It is well known that currents are difficult to detect directly in radar images. However, it is often possible to detect manifestation of a current by its impact on internal wave field, by the character of "wake-like" features and vortex streets behind islands, and by spatial patterns of natural and spilt oil slicks. Observation of internal waves transformation by non-uniform large-scale currents is considered. Specific manifestations of internal waves front distortions can be caused by the following phenomena: the influence of bottom relief, variability of water density, wave-wave interaction and refraction on the horizontally non-uniform large-scale currents. Radar data clearly demonstrate unusual disturbances of internal solitons' fronts, which cannot be explained by bottom topography. The theoretical considerations show that the influence of stratification variability is weaker than the currents influence. For that, we assume that observed distortions of internal waves fronts are caused by transformation on the oceanic currents. Available radar images obtained in the Bering Strait display a large variety of surface manifestations of vortex streets downstream Fairway Rock and lee waves from Diomede Islands connected with the variability of the run-against flow. Based on well-known theoretical hypothesis, results of laboratory experiments, and analysis of radar data the estimation of speed and direction of sea currents has been done. Summer/autumn concurrent experiments conducted near Gelendzhik, Black Sea shore, allowed to qualitatively estimate the sea current characteristics from the analysis of surfaces slick manifestations in radar data.