The Optimal Selection of GPS Double-Differenced Measurements for GRACE

The GRACE mission currently generates approximately 150,000 GPS double-differenced measurements each day from a network of roughly fifty ground stations. The volume of data collected from these ground stations far exceeds the number of inter-satellite range measurements collected and processing these GPS measurements consumes the bulk of the computing time involved in estimating the gravity field. The GPS data only influence the recovery of the low to mid degree gravity signals, with most of the gravity signal being determined from the inter-satellite range measurements. The limited contribution of the GPS measurements, along with the significant computing time required to process them suggest that a strategy be developed by which only the minimal set of GPS measurements required be processed. The purpose of this study is to demonstrate that a reduced ground station network, combined with an optimal GPS parameterization, will provide a quality gravity field solution which satisfies the overall mission requirement with much greater processing efficiency