A Global Look At Earth’s Surface Waters

Artistic rendering of the SWOT satellite. Image Credit: NASA/JPL

September 21, 2017 – While Boulder battled temperatures in the high 90’s this summer, CIRES ESOC researcher J. Toby Minear and his team were knee-deep in frigid Alaskan waters—taking calibration ground measurements for a NASA mission that will harness new, state-of-the-art satellite technology to view Earth’s water in incredible detail from space.

Once fully operational, the NASA Surface Water and Ocean Topography (SWOT) mission will remotely capture accurate, cutting-edge detail about the world’s rivers, wetlands, and oceans—far beyond what has been recorded by previous technology. The satellite is scheduled to launch in 2021.

“We will have the potential to make measurements at accuracies and scales that we have never made before.” said Minear. “Studying river and lake levels without having to physically travel to the field will now be possible—and that’s unheard of.”

Across the globe, less than five percent of the world’s major rivers are instrumented with gauges to measure their discharge. Even well-known rivers like the Congo lack this type of equipment; Currently scientists do not have an accurate measure of the volume of water that rushes through the mouth of that African giant.

SWOT will help researchers and decision makers overcome these limitations: A collaboration between the United States, France, Canada, and the United Kingdom, SWOT is the first ever satellite mission dedicated to hydrology. The satellite will harness a new, high-precision radar frequency to view rivers with incredible resolution: this “Ka-band” frequency uses tiny, millimeter-sized radar waves to measure water levels and flooding at centimeter level—that’s much more precise than previous methods.

This summer, NASA’s AirSWOT aircraft carried a prototype of the satellite’s main instrument—allowing researchers to test the instrument before the satellite launches into space. The AirSWOT plane was one of several participating in a large multi-sensor NASA project investigating the rapidly changing Arctic and boreal environments in northern latitudes, called ABoVE (Arctic-Boreal Vulnerability Experiment).

Back in the field, dressed in a water-tight drysuit—Minear and his team measured water-levels by raft and kayak in the Sagavanirktok River, which drains into the Arctic Ocean. Using highly precise GPS instruments linked to acoustic river current profilers, Minear and his team simultaneously measured water elevation, depth, velocity, and discharge. Other teams around the world made similar “ground-truth” measurements this summer—by drone, in rivers, in other aircraft—to help NASA calibrate, validate, and fine-tune methods in preparation for the SWOT mission.

Team members Mylene Jacquemart (CU) and Brandon Overstreet (USGS) measuring GNSS antenna offsets for the Acoustic Doppler Current Profiler (ACDP). Image Credit: J. Toby Minear/CIRES

Once launched, the SWOT satellite will unleash a new wave of improved hydrological data and make it accessible worldwide. Scientists and decision makers in places that currently lack river gauges will be able to access data remotely, to help fuel research and water resource decisions. In the United States, that means experts with the U.S. Geological Survey, Bureau of Reclamation, and the Army Corps of Engineers will have vastly expanded ability to measure freshwater variables such as lake level and river discharge.

CIRES is a partnership of NOAA and CU Boulder. The CIRES Earth Science & Observation Center advances scientific and societal understanding of the Earth System based on innovative remote sensing research.