Analysis of submarine sand wave imaging by SAR in Taiwan shoal

Abstract

In this paper, submarine sand wave imaging by SAR in Taiwan shoal and their relationships with sea surface wind and sea surface current are discussed. A total of 69 synthetic aperture radar (SAR) images over 11 years between 1996 and 2006 are collected and 496 profiles of sand wave SAR images are used for the observations of sand wave SAR images. The sea surface wind estimated from NCEP/QSCAT blended wind data and the sea surface current calculated form highfrequency (HF) radar system are utilized for the study on the observations of sand wave SAR images with the wind speed and current speed. The results show submarine sand waves in Taiwan Shoal are mainly distributed from 117.75°E to 118.70°E and 22.7°N to 23.35°N with a high percent of 72.2. About 91% of sand waves are observed by SAR under wind speed of 9 m/s while only 6% of sand waves are imaged above wind speed of 10 m/s. And under the adverse wind direction, the observed sand wave reaches its maximum, while the crosswind has its minimum. These support that low and middle wind speed and adverse wind direction are favorable for SAR imaging submarine sand waves, high wind speed and crosswind are unfavorable. The observations of sand wave SAR images reach its seasonal maximum with a percentage of 49 in summer and have its minimum in autumn with 8%, while spring and winter has percentage of 20 and 23 respectively. The comparisons for monthly mean sea surface wind speed and monthly mean sea surface current speed with observed sand waves also shows strong relationships, which are lower sea surface wind speeds and higher sea surface current speed, the higher probability of sand waves observed by SAR. This may indicate that the higher observation of the sand waves by SAR is partly due to wind speed and current speed.