Research on Sea Level and Rising Trend of Coastal Waters in China

The mean sea level is very important to national height datum and the research into variation of the sea level is a basic branch of geodynamics.The relative variation of the sea level is a key point of disaster reduction and prevention as well as large scale engineering construction.From the geodynamic point of view,however,sea level is not a static surface.It is effected by the variation of global atmosphere temperature and the dynamic changes in and outside the earth.The observations by tide gauge stations or any other technique seem rough and discontinuous due to many unknown short outlying events,for example,windstorm,roar,typhoon,storm,huge waves tsunami and eddy,etc.All the abnormal characteristic of the sea surface at a measurement moment produces unfavourable effect on the final estimate of the sea level and its dynamic variation parameter.The classic treatment of the observations in tide gauge is mainly based on Least Square (LS) and corresponding hypothesis testing.It is well known that the result obtained by LS can be seriously influenced by outliers.Any gross errors or outliers involved in the sea surface observations can distort the estimated results of mean seal level and its dynamic movements.As the robust estimation theory has been applied to many fields,such as Geodesy,the main purpose of this paper is to apply robust estimation theory to construct a robust calculation procedure based on the dynamic model,which can retain the dynamic information from the complex observations and resist the harmful effects involved in any observations. Therefore,the dynamic robust model is established for determination of mean sea level and rising trend.The model not only considers the dynamic variation of the sea level,but also controls the gross errors or anomaly variation in sea level observations.Then the dynamic robust model is compared with the average method,robust estimation and dynamic estimation model,and practical observations are computed and result shows that it is more reliable and superior to the classic method.Finally,the mean sea level and rising trend are computed based on the long-term observations of 42 tide gauge stations in China from 1950s to 1970s,and the result of the amplitute of rising trend is 0.621mm annually during the decades.