Measurement of the sea surface using a GPS towing-body in Wanshan area

Wanshan area has been chosen to be the specified field to calibrate and validate (Cal/Val) the HY-2 altimeter and its follow-on satellites. In March 2018, an experiment has been conducted to determine the sea surface height (SSH) under the HY-2A ground track (Pass No. 203). A GPS towing-body (GPS-TB) was designed to measure the SSH covering an area of about 6 km×28 km wide centered on the HY-2A altimeter satellite ground track. Three GPS reference stations, one tide gauge and a GPS buoy were placed in the research area, in order to process and resolve the kinematic solution and check the precision of the GPS-TB respectively. All the GPS data were calculated by the GAMIT/GLOBK software and TRACK module. The sea surface was determined by the GPS-TB solution and the tide gauge placed on Zhiwan Island. Then the sea surface of this area was interpolated by ArcGIS 10.2 with ordinary Kriging method. The results showed that the precision of the GPS-TB is about 1.10 cm compared with the tide gauge placed nearby, which has an equivalent precision with the GPS buoy. The interpolated sea surface has a bias of −1.5–4.0 cm with standard deviation of 0.2–2.4 cm compared with the checking line. The gradient of the measured sea surface is about 1.62 cm/km along the HY-2 orbit which shows a good agreement compared with the CLS11 mean sea surface (MSS). In the Cal/Val of satellites, the sea surface between the tide gauge/GPS buoy and the footprint of altimeter can be improved by this work.