Measuring Earth's Surface Water

NASA launches mission to measure Earth’s surface water – with help from Canada

(Article courtesy of The Globe and Mail)

A spacecraft equipped with Canadian technology has begun its mission to answer one of the most basic but challenging questions in climate science: where is all the water?

The Surface Water and Ocean Topography mission, or SWOT, was launched from California’s Vandenberg Space Force Base early Friday morning aboard a SpaceX Falcon 9 rocket. The low-Earth-orbit satellite was developed by NASA in partnership with the French space agency, CNES, with additional involvement from Britain and Canada.

SWOT’s aim is to measure the water levels of rivers, lakes and coastal waters of about 90 per cent of the globe and track how they change over time.

While the task may sound straightforward, the results promise to unlock a bounty of information about the water cycle, its relationship to climate and the consequences for people around the world.

Indeed, so important is the data that the scientists behind the mission describe it in the same terms that astronomers have used when talking about the James Webb Space Telescope.

“We’re speaking about a revolution in hydrology,” said Selma Cherchali, the head of Earth observation at CNES, at a prelaunch science briefing.

For decades, researchers have been able to rely on satellite imagery to measure the length and breadth of the countless bodies of water that dot Earth’s surface and to map the coastlines of every continent, but capturing water levels is an entirely different matter. Visually, there is no easy way to do this from space.

Instead, gauges that measure water levels must be installed wherever such data is needed. However, that can only provide measurements at one point, and the global distribution of gauges is highly uneven, leaving many parts of the world underrepresented in the data.

Without water level data, estimating the total volume becomes guesswork – which in turn makes it difficult to answer a host of questions about drought, flood risk and water availability in many locations.

“Having these areas where there’s a dearth of information is horrible to deal with because you’re just left having to make assumptions,” said Thomas Piekutowski, the program manager for Sun-Earth system sciences at the Canadian Space Agency.

SWOT has been designed to bridge this knowledge gap by using a pair of antennae 10 metres apart that simultaneously fire radar pulses toward Earth’s surface thousands of times per second. The pulses are reflected by water and travel back up to the spacecraft.

The slight difference in the time it takes the reflected pulses to reach each antenna separately allows the satellite to extract three-dimensional information about water levels to an accuracy of within 10 centimetres.

The satellite’s near-polar orbit allows it to build a global map of Earth’s water every 21 days. It is expected to provide data on any body of water that is at least 250 metres across, including small lakes and most of the world’s major rivers.

“That’s critical in a country like Canada that has millions of lakes and rivers that would be impossible to measure by traditional, ground-based methods,” said Jay Famiglietti, executive director of the University of Saskatchewan’s Global Institute for Water Security.

During the development of SWOT, researchers tested the satellite’s radar system by flying it over some of Canada’s Prairie wetlands.

SWOT is also designed to observe the oceans and record the degree to which the sea surface is lifted or depressed by eddy currents that can transport heat, nutrients, oxygen and pollution from one place to another, providing a unique window on the ever-shifting patterns of water flow.

Collectively, the data will improve climate models and help researchers understand the global water supply.

“It’s really going to provide rich information that impacts all of us,” said Benjamin Hamlington, a research scientist at the Jet Propulsion Laboratory in Pasadena, Calif., and a member of the SWOT science team.

Environment and Climate Change Canada and the Department of Fisheries and Oceans are both preparing to make use of the data SWOT will provide. The Canadian Space Agency is also working with university researchers with projects related to SWOT.

Canada has contributed a key electronic component to the satellite called a klystron, which amplifies the radar signal. The hardware was built by Communications & Power Industries Canada Inc., a Georgetown, Ont., based company.

The launch caps off a big year for Canadian researchers engaged in observing the planet and its atmosphere from space. 

In October, the federal government announced about $200-million in funding for a new mission called HAWC, so named because it is designed to study high-altitude aerosols, water vapour and clouds. All are factors that influence how energy moves through the atmosphere. Scientists are seeking a better understanding of their distribution and impact to refine climate models.

“Having better data is really going to be critical,” said Kaley Walker, an atmospheric physicist at the University of Toronto and co-principal investigator on the project.

The effort is part of a multi-satellite program, the Atmosphere Observing System, led by NASA. Some components of HAWC are slated to fly in 2028, with a Canadian-led satellite to follow in 2031.