Satellite Radar Altimeter Waveform Retracking Of Waveform Derivative Method And Derivation Of Gravity Anomalies

Satellite altimetry,developed by satellite remote sensing technology,has a wide range of applications in earth science.Deriving marine gravity is one of the important applications of satellite altimetry.The high-resolution marine gravity derived from satellite altimetry has provided a new understanding of the topography and tectonics of the ocean.With the improvement of marine gravity derivation theory,the accuracy of gravity anomalies from satellite altimetry is mainly depends on the quality of altimeter data.Waveform retracking is an important method to improve the quality of altimeter data both in the open ocean and coastal areas.However,the existing waveform retracking methods are not always the optimal method when dealing with the satellite altimeter data over the unverified areas.Therefore,this paper proposed a new method of waveform derivative retracking.Based on the altimeter data from Jason-2 Expeact Repetitive orbit Mission(ERM)around the South China Sea region(105°?125° E,0°?30°N),the sea surface height(SSH)was retracked by the waveform derivative method,and the quality of the retracked SSH was evaluated.Combining waveform singular value decomposition denoising and waveform derivative retracking,the altimeter data from Jason-2 Geodetic Mission(GM)was retracked.Based on the retracked SSH,the gravity anomalies with grid of 1'×1' are determined by the least squares collocation(LSC)method around the South China Sea.The main contents and innovations are as follows:(1)Based on the theoretical waveform model,the parameter formula of the leading edge midpoint is derived from the waveform derivative method,and a new waveform retracking method is proposed.According to the measured waveform,the processing procedure of the waveform derivative method is given.Furthermore,in order to reduce the waveform noise and improve the accuracy of retracking,a waveform derivative method based on the first-order difference quotient of the waveform is given.(2)The waveform derivative method was used to retrack the altimeter data from Jason-2/ERM in the South China Sea,which improved the quality of the SSH.Based on the SSH crossover discrepancy,the root mean square error(RMS)of the crossover discrepancy obtained by the waveform derivative method is less than the results obtained by the OCOG,5-?,Threshold,Ice-1,MLE3,and MLE4 conventional waveform retracking methods.Based on the assessment of along-track geoid heights,the retracked SSHs obtained by waveform derivative method have a strong correlation(>0.9)with the geoid heights,and the SSH improvement percentage(IMP)is better than the results of conventional methods.It's show that the retracked SSH by the waveform derivative method has better smoothness than the retracked SSH by other methods.Based on the assessment of tide gauge records(Quarry Bay tide gauge record and Kaohsiung tide gauge record)in the coastal area,the height anomaly obtained by the waveform derivative method has a high correlation(>0.85)with the height anomaly obtained by tide gauge record,and the RMS of the difference is smaller than the results obtained by conventional waveform retracking methods.(3)On the basis of waveform singular value decomposition denoising,the waveform retracking of waveform derivative method is proposed.Based on the retracked high-resolution SSHs from Jason-2/GM,the gravity anomalies are derived by the LSC method over the South China Sea,which improved the accuracy of gravity anomalies.The waveform derivative method and the conventional waveform retracking methods were used to process the denoised waveform obtained by the different singular percentage value of SVD.Based on the standard deviation of the retracked SSHs,it is show that the waveform SVD denoising with a singular value of 80%is beneficial to improve the accuracy of retracked SSHs.In the process of using the LSC method to determine gravity anomalies,the gravity anomalies were calculated by the retracked SSHs within the different spherical distances.It is show that the optimum widow of this paper is selected as 0.8°.(4)Based on the ship-borne gravity data provided by the U.S.National Center for Environmental Information(NCEI)and the Second Institute of Oceanography(SIO),Ministry of Natural Resources of P.R.China,as well as the global marine gravity models V27.1 and DTU13,the improved accuracy of Jason-2/GM-derived gravity anomalies were verified.The RMS difference between Jason-2/GM-derived and NCEI ship-borne gravity is 5.8mgal,and is 2.9 mGal when replacing the NCEI ship-borne gravity from the SIO value.It is basically consistent with the performance of marine gravity models V27.1 and DTU13 in comparison with the ship-borne gravity.Based on the NCEI ship-borne gravity over the open ocean,the accuracy of the gravity anonalies is improved by 1.1mgal after waveform derivative retracking.In the coastal areas,the accuracy of gravity anomalies is improved by 1.5mGal after waveform derivative retracking.The improved accuracy is better than the results obtained by OCOG,Threshold and 5-? method of waveform SVD denoising.Compared with global ocean gravity field model V27.1 and DTU13,the accuracy of gravity anomaly in different ranges away from the coastline is further verified.