The propagating speed of internal solitary waves investigated by X-band radar near Dongsha island

Shipboard X-Band radar images acquired on June 24th, 2009 are used to study internal solitary waves (ISWs) characteristics at northeast of the South China Sea (SCS). The studied images show one ISW in a packet. A methodology based on the Radon Transform (RT) technique is introduced to calculate internal wave parameters such as direction of propagation, internal wave velocity from backscatter image. The result shows that the ISW amplitude is more than 100 meters and it approximately propagates northwestward continent shelf at a speed of 3.04 m/s. Compared with the other researches, especially only with satellite remote sensing images, the ISW propagation speed we got seems higher than other results. A new explanation is presented among different remote sensing images. The periods of most internal waves at northeast of SCS acquired from SAR images aren´t regular M2 tidal period (T = 12.4h), but less than 12.4h. This may be the reason that the ISW propagation speed we got from X-band radar images is higher than others from SAR images.