Land surface water is a major component of the hydrological cycle and the source for over 66% of the water consumed by humans, but yet amounts to less than 1% of the total water on Earth. Monitoring of continental surface water is a major issue for national, state, and local governments and of paramount importance for hydrology science to understand climatic changes and the impact on humans and biodiversity. Satellite altimetry has long contributed to the monitoring of continental surface water, specifically providing surface water elevation observations of inland seas, lakes, rivers, reservoirs, and wetlands. These elevation observations have contributed to several hydrology products including lake and reservoir volume change, river stage and discharge, river elevation profiles and in situ station leveling, and wetland water levels. The geodetic altimeter elevation observations collected by GEDI are an important data set to add to the global monitoring of land surface water. The GEDI data set is unique as it provides sub-kilometer spatial sampling with large footprint lidar measurements of surface water elevation without penetration into the water column. Multi-track, high-resolution, along-track sampling makes GEDI data especially useful for measuring river reach slopes.

The world’s land ice in the form of glaciers, ice caps and the Greenland and Antarctica ice sheets are a major contributor to global sea level rise (GSLR). From 1992 to 2010 the Greenland and Antarctic ice sheets have accounted for approximately 20% of GSLR. More recently from 2004 to 2016 the ice sheets have contributed approximately 35% of GSLR. However, over the next 100 years mountain glaciers and ice caps will contribute more to GSLR than the ice sheets combined, with approximately 60% of the of ice loss from glaciers and ice caps potentially accounting for 37 cm of GSLR over the next 100 years. In fact, the next largest contributor to present day GSLR is from the Gulf of Alaska glaciers which contribute approximately 7% to GSLR. While the ISS orbit precludes GEDI from observing the polar land ice, GEDI observes the most susceptible and dramatically wasting sub-polar land ice, including the high mountain Asia and Patagonia glaciers and ice caps. The Patagonia ice fields are rapidly losing volume with current recent estimates of ice loss equivalent to 2% of GSLR from these ice fields alone. The high mountain Asia glaciers are the world’s largest storage of frozen water in the sub-polar region, and as such are an important water source for millions of people. Rising temperatures have forced rapid ice loss in the region with a conservative estimate of nearly a third of the ice lost by the end of the century. GEDI’s multi-beam large footprint surface elevation observations provide measurements of the sub-polar land ice to aid in understanding their present state and future change. Similarly, the sub-polar snowpack is an important water resource and GEDI’s surface elevation measurements contribute to validating and mapping this snowpack.

Ice calved from the Upsala glacier. Image credit: NASA

Coastal topography is a key parameter driving coastal change processes and in quantifying the inundation and impacts from sea level rise, storm surge, and tidal flooding. Understanding the impact of regional and local sea level rise requires precise land topography measurements linked to sea level in a precise reference frame. GEDI provides a plethora of large footprint surface elevation measurements at the ocean land interface. GEDI also provides these measurements for remote and highly vegetated coastal regions. These high accuracy surface elevation observations can then be used to control and improve coastal digital elevation models relative to sea level for the purposes of local and regional flood modeling from sea level rise, tidal flooding, and storm surge and quantifying hurricane hazard zones.

Mangrove forest in Pongara National Park in Gabon, Africa, photographed during NASA’s 2016 AfriSAR mission.