Minimize Heritage

The Poseidon-4 radar altimeter has evolved from the altimeters on-board the Jason satellites (Poseidon-2 of Jason-1, Poseidon-3A of Jason-2 and Poseidon-3B of Jason-3). Poseidon-4 also inherits the Synthetic Aperture Radar (SAR) High Resolution Altimeter mode of CryoSat-2 SIRAL (SAR Interferometry Radar Altimeter) and Sentinel-3 SRAL (SAR Radar Altimeter). SAR altimeters are now proven to provide data allowing reduction of errors in retrieval of elevation and SWH retrieval over opena and coastal ocean. Poseidon-4 is supported by a MicroWave Radiometer (AMR-C) for atmospheric correction and a Precise Orbit Determination (POD) package, including a GPS/Galileo receiver (GNSS-POD), a DORIS instrument and a Laser Retro-reflector Array (LRA).


The combined topography package provides exact measurements of sea surface height, essential for ocean forecasting systems and climate monitoring. SENTINEL-6 will also provide accurate topography measurements over rivers and lakes.


Even though POSEIDON-4 inherits technology from SIRAL, POSEIDON-3 and SRAL, it has many new features. The main innovations of POSEIDON-4 with respect to its predecessors are:

  • Improved digital and radio frequency hardware that improves performance.
  • Open burst Ku-band pulse transmission (open burst operation, termed the interleaved mode): performing a near continuous transmission of Ku-band pulses. It will allow simulations processing of the measuurements to obtain High Resolution along-track (HR or SAR) and Low Resolution along-track (LR or LRM) data.
  • Dual frequency transmission: transmits C-band pulses in order to retrieve a correction for ionospheric path delay.
  • Implementation of an On-board algorithm termed - "Range Migration Compensation" (RMC) reducing overall data volume.

For the purpose of minimising long-term drifts that can alias in-to sea-level elevation retrieval. 20 calibration pulses per second are generated.


 Figure 1‑2: (Top) Closed burst operation as implemented on SENTINEL-3 (SRAL) and CRYOSAT (SIRAL). The instrument transmits a burst of pulses (64 in this case) and waits before receiving returned echoes. This concept suits topography missions such as that of CryoSat. (Bottom) Open burst operation allows continuous transmission of pulses interleaved with receive echoes, hence the term 'interleaved mode'. (Credit: NOAA)