ACCURACY ASSESSMENT AND REFINEMENT OF THE JGM-2 AND JGM-3 GRAVITY FIELDS FOR RADIAL POSITIONING OF ERS-1

ERS-1 radial positioning using the JGM-2 and JGM-3 gravity fields is a ssessed by analysing dual crossovers with TOPEX/Poseidon, neither fiel d containing ERS-1 data. This method allows a more complete recovery o f ERS-1 radial orbit error, specifically of the previously unattainabl e mean geographical error. The global analysis shows that the theoreti cal error derived from the JGM-2 covariance matrix is realistic and th at JGM-3 represents a slight improvement, at least at the inclination of ERS-1. A latitudinal-based study in the southern ocean indicates po ssible weaknesses in both fields, notably for low and resonant geopote ntial orders m. A refinement of JGM-2, RGM-2, is undertaken through in clusion of ERS-1 and STELLA laser tracking and ERS-1 altimetry, reduci ng several of its deficiencies.