Impact of range scale factor and baseline biases on gravity field estimation: analysis and validation with GRACE follow-on data and simulations

Abstract

GRACE/GRACE-FO missions recover gravity field from orbits observed by GPS and variations in inter-satellite distances obtained by the inter-satellite ranging systems. Compared to GRACE, GRACE-FO is also equipped with a laser ranging interferometer (LRI), a more precise inter-satellite ranging technology and the preferred choice for future gravity missions. While the majority of studies predominantly focus on stochastic errors, this research highlights the critical role of non-stochastic biases, specifically the range scale factor for the K-Band ranging (KBR) and LRI data, and baseline biases in GPS observations, i.e., offsets over the ~200 km separation. The effects of range scale factor and baseline biases on the gravity field spherical harmonic coefficients (SHCs) are evaluated through simplified bias models (SBM). We demonstrate that baseline biases exert an influence on the SHCs in a manner analogous to that of the range scale factor. At low SH degrees (2–8), range scale factor and baseline biases impact SHCs approximately proportional to the static gravity field coefficients. The SBM agrees well with error-free simulations, but deviations appear at higher degrees (8–60) when background model errors are included and scale biases are below 1 ppm. Additionally, the effectiveness of the SBM is validated using real GRACE-FO data. A strong correspondence was observed between the scale factor corrections and the C20 relative errors, which provides a practical basis for error budgeting in future missions. These findings indicate the significant impact of scale factors and baseline biases on gravity missions, which can be effectively evaluated using the SBM presented here.