New Paper Pinpoints Key Role of NASA Satellites in Monitoring Earth’s Vital Signs

A laser altimeter is a precise tool for measuring Earth’s topography, capturing the height and shape of a specific area on the Earth’s surface. A satellite shoots a laser beam from space, illuminating a certain area and then bouncing back. The height of the target area comes from how far the laser travels and how long it takes to bounce back. If there is vegetation on the surface, it estimates the canopy height and structure, as well as the ground.

The new research, published Jan. 30 in Nature Reviews Earth & Environment, illustrates the impact of satellite laser altimetry to monitor the full Earth system. This laser technology is deployed on satellites or the space station, ensuring it remains unaffected by international borders. It collects essential data on critical Earth components such as melting ice, sea-level changes, carbon levels in forests around the globe, and the amount of aerosols in the sky.

"We know from 20 years of observation that this is a great technology that can tell stories about our planet through data with unprecedented accuracy and resolution," said Lori Magruder, an associate professor in the Cockrell School of Engineering's Department of Aerospace Engineering and Engineering Mechanics, and the lead author of the research.

Measuring a changing planet

Earth is made up of different components that work together: living things (biosphere), oceans and water on land (hydrosphere), the air around us (atmosphere), icy areas like ice sheets and glaciers (cryosphere), and the ground beneath our feet (geosphere). Figuring out how these components interact and change with time is crucial to figuring out how things might change in the future and understanding the part humans play in those changes.

NASA’s three satellite missions, two of which are ongoing, have provided global surface and canopy heights. This has enabled scientists to quantify the annual loss of 320 gigatons of land ice from Greenland and Antarctica from 2003 to 2018, representing a 14-millimeter-rise in sea level, and a 30% reduction in winter sea ice volume in the Arctic from 2003 to 2021. Outside the polar regions, water surface heights have shown that human-managed reservoirs account for 57% of Earth's seasonal surface water storage variability, while Earth's forests act as a net carbon sink, compensating for losses through forest growth.

“Satellite altimetry has led to so many discoveries and is vital for monitoring the health of the planet,” said Fricker, who also co-leads the Scripps Polar Center. “We are living during a critical time in Earth’s history, where rapid changes are occurring due to the effects of climate change from increasing greenhouse gases in the atmosphere. Humans urgently need better ways to track and predict how Earth is changing — and satellite-based lasers provide this capability.”

NASA’s original laser altimetry mission, ICESat, ran from 2003 to 2009. Its successor, ICESat-2, launched in 2018 and remains active today. These missions are complemented by the GEDI mission, which also remains active.

Scientists at Scripps Oceanography and the University of Texas at Austin (UT) have a rich history of involvement in laser altimetry missions. Over the past decade, Scripps Oceanography’s Fricker has played a crucial role as a member of NASA’s Science Definition Team, contributing to the success of the ICESat-2 satellite launch and recently being appointed as a science team leader.

Bob Schutz, a former aerospace engineering faculty member at UT, was chosen as the original science team lead on ICESat. Magruder and Amy Neuenschwander, a co-author on the paper and senior research scientist at UT's Center for Space Research, are both part of the science team for ICESat-2 that Magruder has led for the past decade.

After ICESat-2 and GEDI, no further laser altimetry missions are on the books. The authors emphasized the efficacy of this technology, and urged sustained support for its continued development and deployment.

Every 10 years, the National Academies of Sciences, Engineering and Medicine publishes the Decadal Survey for Earth Science and Applications from Space (ESAS), which will help shape science priorities and guide agency investments into the next decade. The survey, sponsored by NASA, the National Oceanic and Atmospheric Administration, and the United States Geological Survey, is driven by input from the scientific community and policy experts.

The 2017-2027 ESAS Decadal Survey highlighted three “targeted observables” that can be served by satellite laser altimetry: ice elevation, terrestrial ecosystem structure, and surface topography and vegetation for consideration for future missions. The next survey is coming up in 2027, and will certainly play a role in the future of Earth science satellite missions and research, said the authors.

"We want to make sure the scientific community understands the impact these missions have made," said Neuenschwander. "These missions will continue to play an important role in understanding the changing nature of our climate and planet as a whole."

Additional co-authors on the paper include Sinead Farrell and Laura Duncanson of the University of Maryland, Bea Csatho of the University of Buffalo, and Sahra Kacimi of NASA’s Jet Propulsion Laboratory.

– Adapted from the University of Texas at Austin

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