June 21, 2023

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, an ultra-precise GPS receiver and a DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) transponder for precise orbit determination.

Le module Nadir de SWOT en cours d’intégration

The C/Ku-band nadir altimeter, a replica of the Poseidon-3 model on Jason-3, was supplied by CNES. It complements the main KaRIn instrument, filling in gaps for long-wavelength ocean signals (>1,000 km). It also aids calibration of KaRIn. Performance is expected to be the same as for Poseidon-3.

L’altimètre Nadir POSEIDON 3C

SWOT is equipped with the same DORIS receiver as Sentinel-3. It affords 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, measures atmospheric water vapour at three frequencies—18, 24 and 34 gigahertz—to improve altimetric accuracy. Water vapour is measured using two beams pointed simultaneously at the centre of the interferometer’s right and left swathes. AMR draws on the heritage of the Jason-2 and Jason-3 missions.

Radiomètre AMR

The Global Positioning System Payload (GPSP) complements DORIS for precise orbit determination. Its performance draws on the heritage of the instrument on Jason-3. The GPS receiver on SWOT is not redundant and a specific feature is that its antenna is integral with the spacecraft 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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