Over years of development, the instrument has been designed to capture very precise measurements of the height of water in Earth’s fresh water bodies and oceans. CARIN will measure the height of water in the ocean, “seeing” features such as currents and eddies that are less than 13 miles (20 kilometers) across — 10 times smaller than are detectable with other satellites in the ocean. It will also collect data on lakes and reservoirs larger than 15 acres (62,500 m²) and rivers wider than 330 feet (100 m).
“For freshwater, it would be a quantum leap in terms of our knowledge,” said Daniel Esteban-Fernandez, CARIN instrument manager at NASA’s Jet Propulsion Laboratory in Southern California. For example, researchers currently have good data on only a few thousand lakes worldwide; SWOT would increase that number to at least a million.
The state-of-the-art CARIN instrument is at the heart of this international mission, the latest in a long-running collaboration between NASA and the French space agency Center National d’Etudes Spatiales (CNES), which includes contributions from the Canadian Space Agency (CSA) and the Canadian Space Agency (CSA). UK Space Agency.
a big picture
So far, researchers looking to study bodies of water have relied on instruments that measure at specific locations — such as gauges in rivers or oceans — or that are space-based, gathering data along a narrow “track” of Earth. Yes, they can see from the classroom. Researchers then have to extrapolate if they want a broad idea of what is happening in the water body.
Carin is different. Radar equipment uses Ka-band frequencies in the microwave end of the electromagnetic spectrum to penetrate cloud cover and the darkness of night. As a result, it can take measurements regardless of the season or time of day. The instrument configuration consisted of an antenna at each end of a 33 ft (10 m) long boom. By bouncing a radar pulse off the surface of the water and receiving the return signal with both antennas, KaRIn will collect data along a 30-mile (50-kilometer) wide swath on either side of the satellite. “With the KaRIn data, we’ll be able to actually see what’s happening instead of relying on these extrapolations,” said Tamlyn Pavelsky, NASA freshwater science lead for SWOT based at the University of North Carolina, Chapel Hill.
The two KARIn antennas will see the same spot on Earth from 553 miles (890 kilometers) up. Since the antennas view a given point on Earth from two directions, the return signals reflected back to the satellite arrive at each antenna slightly out of phase or in phase with each other. Using this phase difference, the distance between the two antennas, and the radar wavelength, researchers can calculate the height of the water that KRIN is observing.
Such a remarkable device demanded a lot from the team that developed it. For starters, stability was needed. “You have two antennas looking at the same spot on the ground, but if their footprints don’t overlap, you won’t see anything,” Esteban-Fernandez said. This was one of the many technical challenges the mission faced in building KARIn.
Engineers also need to know how the SWOT is positioned in space to ensure the accuracy of KRIN’s data. If researchers don’t know that the spacecraft is tilted, for example, they can’t account for it in their calculations. “Imagine the boom rolls as the spacecraft moves, so one antenna is slightly higher than the other,” Esteban-Fernandez said. “This will screw up the results—it will look like all your water is downhill.” So engineers included a high-performance gyroscope on the satellite to account for changes in the SWOT position.
The engineers designing the CARIN 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 1.5 kilowatts, which is a huge amount of power for a satellite like this,” Esteban-Fernandez said. “To generate that, you have to have tens of thousands of volts conducting at the satellite.” Engineers need to use specific designs and materials for high-voltage systems when building electronics to help the satellite accommodate such high-power and high-voltage requirements.
The team spent years overcoming those and many other challenges to deliver the KARIn tool. Very soon the interferometer will fly aboard the SWOT satellite for the first time and begin sending back terabytes of data. Esteban-Fernandez said, “Carin will be offering something to the table that didn’t exist before.”
more about the mission
Scheduled to launch from Vandenberg Space Force Base in Central California on December 15, SWOT is being developed jointly by NASA and CNES with contributions from the CSA and the UK Space Agency. JPL, which is managed for NASA by Caltech in Pasadena, California, leads the US component of the project. For the flight system payloads, NASA is providing the Ka-band Radar Interferometer (KaRIn) instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer and NASA instrument operations. CNES is providing the Doppler Orbitography and Radioposition Integrated by Satellite (DORIS) system, the Dual Frequency Poseidon Altimeter (developed by Thales Alenia Space), the KRIN radio-frequency subsystem (with Thales Alenia Space and with the support of the UK Space Agency). , Satellite Platform and Ground Control segments. CSA is providing KaRI in high-power transmitter assemblies. NASA is providing the launch vehicle and related launch services.
To learn more about SWOT, visit: