The Processing Of Multi-generation Altimeter Data And Its Application In Sea Level Changes Monitoring

In the past 20 years,the global sea level is rising faster than ever before.It's a great threat to the resident's safety and environmental stability in the coastal areas.Therefore,it is critical important to monitor the sea level changes.Compared with the traditional tide gauge station,the satellite radar altimeter has the advantages of global coverage,high precision and harmonious measurement,and has become the main tool of global sea level change monitoring.Altimeter data from Topex/Poseidon and its follow-on missions Jason-1/2/3 is retrieved to generate the gridded product.The processing technologies of altimeter data and the application are discussed in this paper.The main work and creative achievements are as follows:1.The processing steps from altimeter data to gridded product:the atmospheric delay correction,geophysical model correction,unified mean sea surface reference and quality control are applied individually to the Geophysical Data Record?GDR?from each mission and calculate the along track sea level anomaly?SLA?data;Then along track gradient and common point averaging are conducted to reduce the spatial-temporal variability in sea level changes;The crosscover point adjustment is applied to different ascending and descending orbits to reduce their systematical biases;And the data from different missions is merged by the joint crosscover point adjustment;the final gridding is processed by the Modified Shepard Method.2.Creative achievements during the procedure:A optimal algorithm is proposed to along track gradient,determining the best-fit interpolation model to improve the accuracy;a new algorithm based on mathematical dichotomy is proposed to determine the location of crosscover,which is more brief and logical;A proper comparison among the most frequent gridding methods is conducted in both offshore sea and open sea.The cross validation shows that the Modified Shepard method is more superior than the others.3.The sea level changes monitoring and analysis:The 1993-2016 sea level rising rate in global oceans is 0.296cm/yr,while the rate is 0.386cm/yr in China Seas,higher than most regions worldwide;the spectral analysis indicates that the SLA in China Seas has a strong 1 year seasonal as well as a 12 and 24 year interannual oscillation;The periodic signal is enhanced with the decline of latitude from the Bo and Yellow Sea to the South China Sea;TheEmpirical Orthogonal Function?EOF?analysis indicates that the seasonal and interannual oscillation in the South China Sea is the strongest in China Seas and a 0.5 year semi-annual oscillation exists in the south of offshore sea of the East China Sea and the whole offshore sea of the South China Sea;The teleconnection between SLA in China Seas and Sea Surface Temperature?SST?in the equatorial Pacific ocean indicates that SLA in China Seas responses to El Ni?o-Southern Oscillation?ENSO?.The 3 month delay SLA in China Seas is constant with the SST in the equatorial Pacific with the correlation coefficient 0.76,under the1^st mode in Singular Value Decomposition?SVD?.Under this circumstance,SLA in the southeast part of the South China Sea shows a significant positive correlation with SST in the equatorial Pacific ocean while SST in the east part of equatorial Pacific ocean shows a significant negative correlation with SLA in China Seas.The result is consistent with in situ observations at the period of ENSO.It could be applied to predict the changing trend of SLA in China Seas.