Waves breaking on sea wall. Credit: Zacarias da Mata

New Sentinel-3 Altimetry Processing Baseline


Photo credit: Zacarias da Mata

Waves breaking on sea wall. Credit: Zacarias da Mata
Waves breaking on sea wall. Credit: Zacarias da Mata

A new Processing Baseline for Sentinel-3 Altimetry, PB 2.79-Marine, will be released on 14 December 2021.

Last Updated

16 February 2023

Published on

02 December 2021

This Processing Baseline (PB) brings improvements and anomaly fixes to the Sentinel-3 Altimetry Marine Products, while not fundamentally changing the timeline.

The updates affect both Level-1 and Level-2 products.

This new PB is still part of Baseline Collection 004, as no major change is expected with respect to the PB 2.61 used for the full mission reprocessing. This ensures the scientific timeline continuity.

Sentinel-3A Sea Surface Anomaly Oct 2021
Figure 1: Example product

SRAL/MWR L2 (v6.52) updates

  • PLRM SSHA corrected.
    • Now the SSB of PLRM is used in the SSHA ('ssha_01_plrm_ku') calculation instead of erroneously using the SAR one. The SSB written in the product has always been correct, it was just wrongly applied in the PLRM SSHA.
  • Mean Sea Surface: Update of CNES/CLS15 to combined MSS solution with SCRIPPS, CNES/CLS15 and DTU15.
    • Default MSS in the SSHA calculation is still DTU18.
  • Mean Dynamic Topography update to CNES/CLS MDT18 model.
  • Angle of Approach to the Coast.
    • New variables 'angle_coast_01', 'angle_coast_20_ku' and 'angle_coast_20_c' added to the L2 product.
  • Addition of Internal Tides correction.
    • New variable 'internal_tide_sol1_01' using 'HREF v8.1' model. Not yet applied into SSHA calculation.
  • Phase Number into netCDF.
    • Same information as it is currently in the manifest.
  • Correction of SAMOSA MQE bug.
    • MQE values were incorrectly low and dependent on wave height. New values are independent for SWH and about 10x the previous one.
  • Pass number corrected.
    • Pass numbers present in the netCDF files are now correct, following the altimetry convention.
  • Fix of filtered ionosphere correction bug.
    • A problem with the filtering algorithm was introducing a variable error of about 0.6mm in the filtered iono correction, both SAR and PLRM.
  • Improvement of the number of measurements for filtered ionosphere correction (STC/NTC).
    • Further filtered ionosphere correction data is now available for STC/NTC timeliness, this impacts mostly coastal zones and sea-ice borders. Users are advised to check if the SSHA generated is impacted by land/ice, for instance with the flags 'open_sea_ice_flag_01_ku'/'open_sea_ice_flag_01_plrm_ku'.

SRAL L1 (v6.21) updates

  • Addition of Zero Masking vector.
    • The new array variable 'stack_mask_vector_l1b_echo_sar_ku' has been introduced and allows to mask out the waveform spurious values of the stack. While it is made available at L1, it is not yet used in the retracking at L2.
  • Longer CAL2 average.
    • The CAL2 is now averaged for 90 days instead of 27 days, this should provide smoother calibration.
  • Small PLRM waveform updates.
    • To fix a truncation issue found. It has zonal impact for range (~1mm) and wave height (~3mm) at L2 retracking.

MWR L1 (v6.12) updates

  • Reduction of ascending/descending bias in the brightness temperatures for 23.8 GHz channel.
    • This should improve the wet troposphere correction at L2, making it slightly more in line with ECMWF’s operational model. The impact expected is less than 1mm.

Overall impact


SAR mode: Difference to previous PB around 1mm.

PLRM mode: Difference to previous PB around 4 mm.

Differences between SAR and PLRM mode are further reduced.

SWH and Wind Speed

Negligible impact for SAR and PLRM modes.

More details can be found in the product notice that will be made available shortly on the Altimetry services page.

There information regarding the current Product limitations can also be found.

The updated Product Format Specification for both L1 and L2 products will be available on the same page.

Acronyms list

Acronym Full name
PLRM Pseudo-Low Rate Mode
SSB Sea State Bias Correction
SSHA Sea Surface Height Anomaly
SAR Synthetic Aperture Radar
CNES Centre National d’Etudes Spatiales
DTU Technical University of Denmark
SCRIPPS Scripps Institution of Oceanography
MSS Mean Sea Surface
MQE Mean Quadratic Error
STC Short Time Critical
NTC Non-Time Critical
ECMWF European Centre for Medium-Range Weather Forecasts
SAMOSA SAR Altimetry MOde Studies and Applications
SWH Significant Wave Height

For more information, contact our User Service Helpdesk.