Evaluation of line-of-sight gravity differences in the MAGIC constellation

Abstract

Standard Gravity Recovery and Climate Experiment (GRACE) and GRACE- Follow On monthly gravity field products provide valuable insights into large-scale mass transport, but their limited temporal resolution constrains the detection of short-lived hydrological extremes. This study applies the line-ofsight gravity difference (LGD) methodology, an along-orbit analysis technique to recover sub-monthly gravity variations using high-precision GRACE-FO Laser Ranging Interferometer (LRI) observations. The key element of the approach is a transfer function that converts observed range accelerations into relative gravity field gradients between the twin satellites, enabling the detection of high-frequency mass variations. Building upon the framework established by Ghobadi-Far et al. (2022), frequencydomain transfer functions are derived using simulated inter-satellite ranging data. Range-rate residuals are computed from GRACE-FO LRI observations and filtered using the transfer function to obtain LRIderived LGD signals. The performance of this approach is evaluated for both a GRACE-like mission and the proposed MAGIC (Mass change And Geosciences International Constellation) configuration. The MAGIC double-pair constellation enhances spatiotemporal coverage, improving sensitivity to regional and high-frequency mass change signals. The methodology is applied to the Kyushu floods (Japan), Yangtze river floods (China) and floods due to Cyclone Amphan (India & Bangladesh), all in 2020. Comparison of LGD signal variations is done with independent hydrologic indicators, including orthometric heights from Ice, Cloud and land Elevation Satellite-2 (ICESat-2) altimetry data and precipitation estimates from Integrated Multi-satellitE Retrievals Global Precipitation Measurement (IMERG GPM). Results suggest spatial and temporal alignment between LGD anomalies and flood-induced surface water increases. This study demonstrates the potential of LGD-based gravimetry and future multi-pair satellite constellations like MAGIC to improve the resolution and responsiveness of satellite-based monitoring of extreme hydrological events.