Sentinel-3 Altimetry A Spot

Sentinel-3 Altimetry instruments

Sentinel-3 Altimetry A Spot
Sentinel-3 Altimetry A Spot

The Sentinel-3 satellites carry the three instruments for the altimetry mission.

Last Updated

20 April 2021

Published on

30 June 2020


Synthetic Aperture Radar Altimeter (SRAL)

SRAL instrument. Credit TAS-F

The dual-frequency (Ku and C-band) Synthetic Aperture Radar Altimeter (SRAL) on board Sentinel-3 provides sea surface topography measurements in SAR (Delayed Doppler) mode, i.e. with a spatial resolution as narrow as 300 m. SRAL is used to determine sea and lake surface height, significant wave height, surface wind speed, and sea ice height and thickness.

Main characteristics

  • Possible radar measurement modes: LRM and SAR (operating 100% in SAR in orbit).
  • Tracking modes: closed and open-loop.
  • Pulse repetition frequency: 1.9 KHz (LRM), 17.8 KHz (SAR).
  • Total range error: 3 cm.
  • Launch mass: 60 kg.

SRAL is supported by a microwave radiometer (MWR) for atmospheric correction and by a Precise Orbital Determination package (POD) to determine the altimeters position in space with pinpoint accuracy.

For further information please see the Sentinel-3 altimetry handbook.


Precise Orbital Determination package (POD)

SRAL requires high accuracy radial orbit detection to meet its operational requirements. The POD package consists of three measurement systems that serve this purpose: the Global Navigation by Satellite System (GNSS), Doppler Orbitography by Radiopositioning Integrated by Satellite (DORIS), and a Laser RetroReflector (LRR).


Microwave radiometer (MWR)

MWR instrument. Credit: ESA

The MWR is a two-channel passive microwave system that records brightness temperatures at 23.8 GHz and 36.5 GHz, providing information on respective atmospheric water vapour and liquid water content. These brightness temperatures are used with a radiative transfer model to infer the amount of water vapour and liquid water in the sub-satellite atmospheric column, and, thus, to calculate the WTC (correction to range) and the atmospheric attenuation (correction to σo) during ground station processing.

Main characteristics

  • Dual frequency, 23.8/36.5 GHz.
  • Radiometric accuracy, 3 K absolute (0.6 K relative).
  • Launch mass: 26 kg.
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Other Sentinel-3 instruments

Other Sentinel-3 instruments

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