Orbit Determination and Gravity Recovery from GRACE-FO GPS Phase-Rate Data: Initial Results from a Novel Processing Scheme using Numerically Differentiated GPS Data

The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission represents the state-of-the-art architecture for satellite gravimetry missions. GRACE-FO consists of a pair of twin low Earth orbiting (LEO) satellites flying in the same orbit with onboard tracking instruments. These instruments can be separated into two categories: low-low satellite-to-satellite tracking (ll-SST) and high-low satellite-to-satellite tracking (hl-SST). The ll-SST instruments consist of the K-band ranging (KBR) and laser ranging interferometer (LRI) which produce precise measurements of the range between the GRACE-FO satellites. The hl-SST refers to the onboard GNSS receivers used for satellite positioning, timing, and long-wavelength gravity field information.

In this presentation, we present initial results from a novel approach to processing GRACE-FO GPS observations. We use a digital filter to numerically differentiate the GPS phase observations to process phase-rate observations instead of processing code and phase range observations. These phase-rate observations are then used for dynamic precise orbit determination (POD) and gravity field estimation in conjunction with the ll-SST observations. We start with a review of previously presented simulation results that motivate this work. This is followed by a detailed description of the data processing, filtering, and observation modeling derivation. We conclude with the initial results from using the GPS phase-rate observations for POD and gravity field estimation. Future work includes detailed error budgeting for this observable as it pertains to POD and gravity recovery. We anticipate these results to be useful in the architecture and science data algorithms for next generation gravimetry missions.