2 8 N ov 2 00 4 On a possible new approach for investigat - ing the secular variations of the low - degree geopotential coefficients

In this paper we try to suggest a possible novel method to determine some selected even zonal harmonics Jl of the Earth’s geopotential. Time series many years long of suitably linearly combined residuals of some Keplerian orbital elements of certain existing geodetic SLR satellites would be examined. A CHAMP/GRACE-only background reference model should be used for the part of the geopotential which we are not interested in. The retrieved values for the even zonal harmonics of interest would be, by construction, independent of each other and of any post-Newtonian features. The so obtained mini-model could, subsequently, be used in order to enhance the accuracy and the reliability of some tests of post-Newtonian gravity, with particular emphasis to the measurement of the Lense-Thirring effect by means of LAGEOS and LAGEOS II.