Retracking Jasonl Altimeter Waveform over China Coastal Zone

摘要

Modern microwave satellite altimeters can measure the instantaneous sea surface height to a precision of approximately 4.1 cm in the open ocean. One limiting factor is that if land appears within the altimeter footprint the data is flagged as useless due to land contamination of the altimeter return waveforms and inappropriate geophysical corrections. This means that many valuable coastal altimetry data values are simply edited out. In order to make improved use of the altimetry waveform data near the coastal area, we derived the altimeter ranges from one year (March, 2006 to February, 2007; cycle 155 to cycle 188) of Jason 1 waveform off the China coast (14-45°N, 105-130°E) by using four specialized retrackers: Ocean, Ice-2, OCOG (Offset Centre of Gravity), and Threshold retracking algorithms, which are employed by Envisat RA2 altimeter standard processing. In order to compare the four retracking algorithms quantitatively, we calculated the bias, root mean square, and standard deviation of the sea level anomaly difference between the ascending and descending tracks at crossovers. In addition, we compared the sea surface height derived from the four retracking algorithms and in-situ tide gauge station measurements. The comparisons showed that the OCOG algorithm provides more accurate results than the other three in coastal waters.