Clark Wilson: Using Satellite to Measure Earth’s Changing Water and Climate

When a pair of satellites only 200km apart can feel the tug of a one‑centimeter‑thick sheet of water half a continent wide, you start to realize our planet has a heartbeat—and that we finally have the instruments sensitive enough to listen to it.

EcoAero recently had the opportunity to speak with Dr. Clark R. Wilson, professor of geophysics at the University of Texas at Austin and a pioneer of “space geodesy.” From early days studying Earth‑rotation variations to steering NASA’s gravity missions in Washington, Wilson has spent nearly five decades turning orbital data into hard evidence of how our climate—and our planet’s mass—continues to change.

Wilson’s fascination with planetary scale studies of earth rotation and related water storage changes began at Scripps Institution of Oceanography and grew as satellite altimetry and laser‑ranged satellites such as LAGEOS came online in the late‑1970s. But it was GRACE—the Gravity Recovery and Climate Experiment launched in 2002—that transformed the field. Flying in tandem, the satellites sense minute changes in the distance between them; those fluctuations reveal shifts in Earth’s gravity field, and therefore in the distribution of mass, most notably water. Over 20 years of monthly “gravity snapshots” have turned GRACE (and its Follow‑On) into an indispensable water‑cycle observatory.

Okay, so that's not very big, but so the whole system, so the system's able to measure changes in gravity on the surface of the Earth with a precision that allows it to see the change in gravity due to a one-centimeter layer of water, about 300 kilometers across.

Wilson’s latest co‑authored paper, published in Science on 28 March 2025, pushes those gravity data further. In a period 2000-2002, just prior to the GRACE mission, using radar altimeters from space to measure sea level change, and polar‑motion records to detect global mass changes, the team tracked an abrupt 1,614‑gigatonne drop in global soil‑moisture storage between 2000 and 2002—an exodus of freshwater as large as two years of Greenland ice loss. That missing water raised mean sea level by ~4.4 mm and nudged Earth’s spin axis ~45 cm toward 90° E—fingerprints strong enough to validate an independent hydrological model and confirm that terrestrial water has been steadily declining ever since.

GRACE’s exquisite sensitivity makes it a very costly mission: two bus‑sized spacecraft, complex microwave and in the follow-on mission laser ranging, and with only one satellite pair flying there are global coverage gaps in space and time. Wilson sees the next leap may be fleets of small sats carrying miniaturized gravity meters or gravity gradient instruments and GNSS‑reflectometry payloads. Swarms could trade individual precision for sheer numbers, stitching together higher‑resolution gravity maps and even bouncing GPS signals off the ocean to watch sea level rise in near‑real‑time. Add machine‑learning‑driven assimilation of climate, soil‑moisture, and atmospheric data, and future systems could flag drought or flood risks before they fully unfold.

Beyond physics, Wilson stresses communication. High‑accuracy sea‑level and water‑storage records face vocal skepticism, yet every smartphone GPS receiver relies on the same Earth‑orientation parameters, including motion of the pole used in his most recent study, all refined by satellite geodesy. Linking daily navigation to long‑term climate measurement closes that credibility gap—turning abstract millimeters into lived reality for coastal planners, farmers, and citizens deciding whether to trust the data.

Dr. Wilson’s work embodies Eco Aero’s mission: harness aerospace innovation to safeguard our shared environment. By spotlighting gravity‑mapping constellations and the soil‑moisture crisis they reveal, we aim to keep the conversation grounded in data—even when that data comes from 400 kilometers overhead. EcoAero will continue following GRACE‑FO’s successors, the emerging nanosatellite geodesy boom, and the AI models poised to convert orbital measurements into actionable climate insight. After all, listening to Earth’s faint gravitational whisper is only the first step; acting on what we hear is the challenge that lies ahead.