Recovery of the gravity field from GOCE data by using the invariants of gradient tensor

The gravity field models GUCASEGM and GUCASEGMDL are established from GOCE data （GOCE Level 2 Products from Nov. 1 to Dec. 31, 2009） based on the method of the invariants of the gravity gradient tensor, where GUCASEGM is derived after GOCE gravity gradient data are filtered with FIR, and GUCASEGMDL is computed with an additional Durbin-Levison arithmetic apart from FIR. Since this method, different from current programs dealing with GOCE data, is introduced for the first time, some new problems are required to be discussed in advance; for example, how to filter GOCE gravity gradient data, how to compute the invariants of the gradient tensor, and how to deal with the pole gap and so on. In addition, by comparing our models with ones recommended by ESA, it can be seen that the variations of GUCASEGM and the models recommended by ESA to EGM08 are almost equivalent, and the variation of GUCASEGMDL to EGM08 is obviously less than ones of the recommended models.