Combining GPS carrier phase and Doppler observations for precise velocity determination

The truncation error and propagation error are analyzed for velocity determination through differential GPS carrier phase observations, and an approach for the choice of the best number of points for the central difference method is developed. In order to overcome the disadvantages of existing GPS velocity determination methods, a new velocity determination algorithm is presented, based on combining carrier phase and Doppler observations. The basic idea is that two types of observation are combined by adding their normal equations, and their weights are evaluated by strict Helmet variance-components estimation. In order to control the influence of outliers, a bifactor equivalent weights strategy is adopted. To validate this method, GPS data of the airborne gravimetry campaign MEXAGE2001 is tested. The results show that the precision and reliability of velocity determination are obviously improved by using the proposed method.