June 29, 2021

Nadir payload

The KaRin instrument is complemented by a Nadir module with a conventional radar altimeter like the C/Ku-band altimeter employed on the Jason satellites, a tri-frequency Advanced Microwave Radiometer (AMR) similar to that on the OSTM/Jason-2 & 3 ocean surface topography mission, GPS receivers and a DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) transponder for precise orbit determination.

SWOT Nadir module undergoing integration

The C/Ku-band nadir altimeter, a replica of the Poseidon-3 model on Jason-3, is being supplied by CNES. This altimeter complements the main KaRIn instrument to ensure nominal coverage of the gaps between KaRIn’s swaths at large wavelengths (> 1,000 km) and also supports calibration of KaRIn’s radar interferometer. It is expected to deliver the same level of performance as Poseidon-3.

Poseidon-3C nadir altimeter

SWOT is equipped with the same DORIS receiver as Sentinel-3. It will afford the ability to measure SWOT’s orbit with centimetre accuracy, thanks to a network of 60 ground stations around the globe.

The Advanced Microwave Radiometer (AMR), built by JPL, will measure atmospheric water vapour at three frequencies—18, 24 and 34 gigahertz—to improve altimetric accuracy. This will be achieved by two beams pointing simultaneously at the middle of the left and right swathes of the radar interferometer. AMR draws on the heritage of the Jason-2 and Jason-3 missions.

Advanced Microwave Radiometer (AMR)

The GPS receiver will complement DORIS for precise orbit determination. This receiver is built around the heritage of the instrument used on Jason-3. The GPS receiver on SWOT will not be redundant and a specific feature is that its antenna is integral with the satellite bus, at the heart of the launcher interface, due to SWOT’s in-flight topology.

SWOT GPSP Receiver (TriG)

The Laser Reflector Assembly (LRA) is a passive unit that reflects laser pulses fired from the ground for calibration purposes. It consists of an optimal array of quartz corner cubes. The LRA is used by some 40 ground laser ranging stations to support the orbital data generated by DORIS and the GPS receiver.


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