Assessing the Performance of GRACE-FO KBR and LRI in Detecting Mass Changes Using Along-Orbit Range-Accelerations

Abstract

Gravity Recovery and Climate Experiment Follow-On is equipped with two inter-satellite ranging systems, notably the K-Band ranging (KBR) and the more precise Laser Ranging Interferometer (LRI), which enable the detection of variations in Earth's gravity. Assessing the differences between KBR and LRI is beneficial for understanding the performance of future LRI-only gravity satellite missions. However, due to limitations imposed by temporal aliasing errors, the advantages of LRI over KBR for monthly gravity field solutions are not clearly discernible. The along-orbit range-accelerations directly reflect the mass variations, providing a new way to evaluate the differences between LRI and KBR. Therefore, we selected different frequency bands and time scales to compare the along-orbit range-accelerations of KBR and LRI from 2019 to 2021. Analyzing the spatiotemporal-averaged along-orbit data, the results indicate a systematic difference between KBR and LRI, with a scale factor of about 0.977 over the selected 92 basins, while the scale factor is lower over oceanic regions. A comparison of the instantaneous along-orbit data for KBR and LRI reveals that the noise level of LRI in the [15.8–21 mHz] band is at least one order of magnitude lower than that of KBR. After simulating instrument noise, model errors, and time-variable signals, it was determined that KBR noise is likely the primary factor contributing to the systematic difference in capturing temporal signals between LRI and KBR. In addition, regions with a low signal-to-noise ratio (SNR) are more susceptible to noise, which diminishes the correlation between KBR and LRI along-orbit data.