Nasa launches water monitoring satellite to provide greater climate insights

Nearly 20 years in development, the Surface Water and Ocean Topography (SWOT) satellite promises to provide a thorough accounting of water over much of the Earth’s surface.

SWOT's measurements of fresh water and the ocean could help researchers to address climate issues and help communities prepare for a warming world.

The data will be compiled from radar sweeps of the Earth that will take place at least twice every 21 days and which could help to bolster weather and climate forecasts.

The satellite makes use of a scientific instrument called the Ka-band Radar Interferometer (KaRIn) which has been in development for years.

The instrument has been designed to capture very precise measurements of the height of water in Earth’s freshwater bodies and the ocean. KaRIn will measure the height of water in the ocean, 'seeing' features such as currents and eddies that are less than 12.5 miles (20km) across – up to 10 times smaller than those detectable with other sea-level satellites.

It will also collect data on lakes and reservoirs larger than 62,500 square meters and rivers wider than 100m across.

“For freshwater, this will be a quantum leap in terms of our knowledge,” said Daniel Esteban-Fernandez, KaRIn instrument manager.

Researchers currently have good data on only a few thousand lakes around the world; SWOT will increase that number to at least a million.

Until now, researchers looking to study a body of water relied on instruments that measure at specific locations – e.g. gauges in rivers or the ocean – or that are space-based, gathering data along narrow 'tracks' of Earth which they can see from orbit. Researchers then have to extrapolate if they want a broader idea of what’s happening in a water body.

KaRIn is a radar instrument that uses the Ka-band frequency at the microwave end of the electromagnetic spectrum to penetrate cloud cover and the dark of night.

As a result, it can take measurements regardless of weather or time of day. The instrument configuration consists of one antenna at each end of a 10m-long boom. By bouncing radar pulses off the water’s surface and receiving the return signal with both antennas, KaRIn will collect data along a swath 31 miles (50km) wide on either side of the satellite.

“With KaRIn data, we’ll be able to actually see what’s happening, rather than relying on these extrapolations,” said Tamlin Pavelsky, Nasa freshwater science lead for SWOT.

The two KaRIn antennas will see the same spot on Earth from approximately 550 miles (890km) above. Since the antennas look at a given point on Earth from two directions, the return signals reflected back to the satellite arrive at each antenna slightly out of step, or phase, with one another.

Using this phase difference, the distance between the two antennas, and the radar wavelength, researchers can calculate the height of the water that KaRIn is looking at.

Engineers designing KaRIn also had to contend with the amount of radar power transmitted.

“To measure things down to centimeter accuracy, you need to transmit radar pulses of 1.5kw, which is a huge amount of power for a satellite like this,” said Esteban-Fernandez.

“In order to generate that, you have to have tens of thousands of volts operating on the satellite.” The engineers needed to use designs and materials specific to high-voltage systems when manufacturing the electronics to help the satellite accommodate such high-power and high-voltage needs.

If all goes as planned, the SUV-sized satellite will produce research data within several months.