Error modeling of bias-type parameters for TOPEX orbit determination

The TOPEX mission has a requirement for a radial orbit accuracy of 13 cm over a 10-day period. To achieve this level of accuracy, accurate dynamic and measurement models are required. A large portion of the orbit error is derived from the uncertainty in the apriori values of the constant model parameters, most notably the geopotential coefficients. In this study, the major sources of model error affecting the orbit accuracy of TOPEX are identified. This includes the use of the full calibrated covariance matrix of the nominal geopotential model.;The results of the parameter identification study are used to design an optimal filter for orbit determination. The primary source of orbit error for TOPEX is identified as the geopotential model error followed by error in the solar radiation pressure coefficient. The optimal filter that is derived in terms of the accuracy of the filter estimates is one that includes the initial conditions of the orbit, single arc parameters for the coefficient of drag and the reflectivity coefficient of solar radiation pressure and multiple-arc parameters for the density correction model.;The accuracy of orbit determination for TOPEX is limited by the geopotential model error which is characterized by the calibrated geopotential covariance matrix. Since the geopotential plays a dominant role in determining the radial orbit accuracy of TOPEX, the methods by which the geopotential covariance matrices are calibrated are reviewed in this study. The conventional methods calibrate the covariance matrix with respect to surface gravity and satellite altimeter data.;A new method is proposed that would adjust the formal covariance matrix generated by a gravity model solution for systematic and random errors that affect the orbit accuracy. Expressions for the consider adjusted covariance matrix are derived for both, the classical least squares and the square-root D-U-Z formulations. The method is applied to generate a consider adjusted covariance matrix of the PGTF2 geopotential model for the TOPEX mission.