Standard GRACE and GRACE-FO 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-of-sight 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), frequency-domain 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 LRI-derived 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) in 2020 and other major flooding events. Preliminary analyses compare LGD signal variations with independent hydrologic indicators, including surface water height anomalies from ATLAS/ICESat-2 ATL13 altimetry data and precipitation estimates from GPM IMERG. Initial 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.