IMPROVEMENTS IN VENUS GRAVITY-FIELD DETERMINATION USING RIDGE-TYPE ESTIMATION METHODS

The objective of this research was to improve the accuracy of the late st gravity field of Venus, labeled VGM6A, through the use of ridge-typ e estimation methods. These advanced parameter estimation techniques w ere applied to the calculation of GM and a (21 X 21) field of harmonic coefficients which represent the gravitational potential of Venus. Da ta used in this analysis, which were supplied by the Jet Propulsion La boratory, were derived from Pioneer Venus Orbiter and Magellan (mappin g cycles 1 and 2) tracking measurements. Calculation of the gravity fi eld coefficients involves solving a large, ill-conditioned system of l inear equations, whose solution leads to erroneous estimates if not au gmented by appropriate a priori information. In calculating VGM6A, Kau la's Rule was used as a basis to determine the a priori covariance use d in the solution process. This study involved the use of ridge-type e stimation methods to optimally weight the a priori covariance establis hed by Kaula's Rule in order to obtain more accurate estimates. The co mputed gravity field, denoted AUVGM6, was compared to VGM6A on the bas is of total variance of the solution, residual sum of squares, and con dition number of the normal matrix. The candidate gravity field was va lidated by the calculation of the Doppler residuals. Analysis of the r esults show that through the use of ridge-type estimation methods, AUV GM6 provides more accurate gravity field coefficients than does VGM6A.