This animation illustrates the movements of the two GRACE-FO satellites as they orbit Earth. As the satellites pass over topographic or mass anomaly features, the relative distance between the satellites changes. This distance change is precisely tracked with the two ranging interferometers: the Microwave Instrument (MWI), as well as the technology-demonstration Laser Ranging Instrument (LRI). Every 30 days, the polar-orbiting satellites gather enough data to derive a global map of the surface mass distribution. The differences in this mass distribution from one month to the next provide fundamental indicators of the large-scale dynamics of the planet as mass (mostly in the form of water) is constantly redistributed within and between Earth’s atmosphere, oceans, groundwater and ice sheets. Since 2018, GRACE Follow-On (GRACE-FO) continues the legacy of GRACE (2002-2017), tracking Earth’s water movement and surface mass changes across the planet. Monitoring changes in ice sheets and glaciers, near-surface and underground water storage, the amount of water in large lakes and rivers, as well as changes in sea level and ocean currents provides an integrated global view of how Earth’s water cycle and energy balance are evolving—measurements that have important applications for everyday life.



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