Analysis of the characteristics of the harmonics coefficient J (2) of the Earth's gravity field in different periods

The characteristics of the geopotential coefficient J (2) in different periods are analyzed using satellite laser ranging data spanning the last 27 years. The satellites used in the analysis are Lageos1 and Lageos2. The variations in J (2) are obtained by determining the dynamic orbit. The results show that there are strong seasonal and long-term variations. For different data spans, the seasonal variations agree well in terms of both amplitude and phase. Using all the data, the amplitude and phase of the annual term are 2.5 x 10(-10) and 127A degrees, respectively, while the amplitude and phase of the semiannual term are 0.94 x 10(-10) and 213A degrees, respectively. In the case of long-term variation, the secular variation in J(2) ((J) over dot(2)) is - 2.2 x 10(-11) a(-1) from 1984 to 2010. 2 differs for the different periods because of interannual variations, such as the "1998 anomaly". Another anomaly may have taken place during 2007-2010. Although the cause of the anomaly is unknown, it is an important observational constraint on the shape of the Earth