Scale Factor Determination for the GRACE Follow-On Laser Ranging Interferometer Including Thermal Coupling

The GRACE follow-on satellites carry the very first interspacecraft Laser Ranging Interferometer (LRI). After more than four years in orbit, LRI outperforms sensitivity of conventional Microwave Instrument (MWI). However, current data processing scheme, product still needs MWI to determine unknown absolute laser frequency, representing “ruler” for converting raw phase measurements into a physical displacement meters. In this paper, we derive formulas precisely performing that conversion from measurement range, accounting varying carrier frequency. Furthermore, dominant errors due knowledge uncertainty frequency as well uncorrected time biases are derived. second part, address dependency on currently employed cross-calibration scheme and present three different models two which largely independent MWI. analyze contribution thermal variations scale factor estimates LRI-MWI residuals. A linear model called Thermal Coupling (TC) is derived, significantly reduces differences between level where observations limit comparison.