Application Research Of Satellite Altimetry Waveforms Retracking Algorithms On The Water Surrounding Taiwan

At present, the accuracy of satellite altimeter measuring the sea surface instantaneous height over the deep ocean is better than±5 cm, this pushed the development of geodesy, geophysics, oceanographic greatly. However, in coastal water the quality of altimetry data decline severely due to the influence of coastal land, ocean topography, geophysical environmental factors, leading to the lack altimetry data in coastal water. Coastal waters affect the human activity very much. So it is necessary to study repairing the coastal altimetry data.In this paper, based on the former research, the 7 years of Jason-1 SGDR waveform data in the waters surrounding Taiwan was processed using the waveform retracking algorithms. The measurement errors caused by the contaminated waveform were corrected. The content and work in this paper are as follows:1,Analysis of the altimetry waveform in the waters surrounding Taiwan, particularly at the junction of sea and land. For two cases that from the land to the sea and from the sea to the land, the changes of altimeter waveform of ground track were analyzed. It is pointed out that using the waveform retracking algorithms to correct the error is necessary.2,The 245th cycle GDR data of Jason-1 on waters surrounding Taiwan were analyzed. It is pointed out that the available altimetry points distribution is independent of the ocean depth. It is related with the distance from the mainland or island. The editorial standards of GDR data were given and then analyzed. It is pointed out that we can establish a flexible editorial standards. The standard can increase the number of effective data.3,Based on analysis of a large number of altimetry waveforms, an intelligent algorithm is introduced in this paper to quantify the distance from the first "polluting" waveform (from water to land) or the first "un-polluting" waveform(from land to water). From the quantitative result, the distances of most data are less than 10km, equivalent of the diameter of altimeter nadir illuminated circle.4,Seven years SGDR waveform data of Jason-1 in the waters surrounding Taiwan were re-processed using the OCOG,5-βparameter and threshold parameter retracking algorithm. The corrections were calculated by the re-tracking algorithms.5,Validation of the effectiveness of altimetry waveform retracking algorithm on the water surrounding Taiwan. The sea surface height anomaly between the corrected altimeter data by retracking algorithm and the neighboring tide gauge data were compared to validate the effectiveness of the waveform re-tracking algorithm. Using Cycle001 pass088 altimetry data as an example, the imp value of OCOG algorithm, 5-βparameter algorithm and threshold are-2.74%,3.64%,5.43% respectively, indicating that 5-βparameter algorithm and threshold algorithm are somewhat effective in correcting the distance. The tide gauge data of the same time with the altimetry data was obtained by linear interpolation. Comparing water level anomaly(WLA) time series of the tide gauge and the sea level anomaly(SLA) time series of the neighboring altimeter nadir, the SLA time series corrected by 5-βand threshold algorithms are more consistent with the WLA time series, the correlation coefficients were 0.8268 and 0.8611 respectively.