Ocean re-tracking estimates - Sentinel-3 Altimetry Technical Guide - Sentinel Online
Two different retrackers have been implemented in the Level-2 processor when operating over ocean:
- LRM: Ocean-3, inherited from JASON-2 mission, is used to perform a fitting of the waveform with a 4-th parametric model estimation (epoch, composite sigma, amplitude and mispinting angle) based on a weighted least square error (LSE) minimization derived from a Maximum Likelihood Estimator (MLE).
- SAR: Fully analytical re-tracker for SAR mode operation over open ocean and coastal zones inherited from SAMOSA project. It tries to fit the theoretically modelled multi-look L1B waveform to the real L1B SAR waveform, providing estimates of the epoch, composite sigma, amplitude and mispointing angle.
The main output of these two retrackers annotated in the Level-2 products are:
- corrected "ocean" altimeter range
- corrected "ocean" backscattering coefficient
- corrected "ocean" significant waveheight
- epoch (used to derive the corrected altimeter range)
- composite sigma (used to derive the corrected backscattering coefficient)
- thermal noise
- square of the angle misspointing
PARAMETER |
Ocean Retracking Outputs |
NETCDF NAME |
epoch_ocean_[x1]_[x2] |
DESCRIPTION |
LRM mode: ocean re-tracking (ALT_RET_OCE_01 algorithm). |
UNITS |
Epoch: 10-15 secs |
DATA SET AVAILABILITY |
Reduced: none |
OPERATING MODE AVAILABILITY |
Epoch: LRM and SAR |
DATA ORIGIN |
1 Hz Ku/C-bands: none |
ADDITIONAL INFORMATION |
None |
PARAMETERS RELATED |
None |
PARAMETER DETAILED DESCRIPTION |
ESA's Global Land and Ocean Mission for GMES Operational Services |
PARAMETER |
Ocean Sea Surface Height Anomaly |
NETCDF NAME |
{ssha_[x1]_[x2]} where: |
DESCRIPTION |
The sea surface height (SSH) above the sea level is only computed for Ku-band measurements. The equation used to compute SSH is: |
UNITS |
10-3 m |
DATA SET AVAILABILITY |
Reduced: 1 Hz Ku-band only |
OPERATING MODE AVAILABILITY |
LRM and SAR |
DATA ORIGIN |
1 Hz Ku-band: ALT_PHY_RAN_02 and ALT_MAN_INT_01 algorithms |
ADDITIONAL INFORMATION |
None |
PARAMETERS RELATED |
None |
PARAMETER DETAILED DESCRIPTION |
ESA's Global Land and Ocean Mission for GMES Operational Services |
PARAMETER |
Corrected Ocean Significant Wave Height |
NETCDF NAME |
swh_ocean_[x1]_[x2] |
DESCRIPTION |
LRM mode: ocean re-tracking. |
UNITS |
10-3 m |
DATA SET AVAILABILITY |
Reduced: 1 Hz Ku-band only |
OPERATING MODE AVAILABILITY |
LRM and SAR |
DATA ORIGIN |
1 Hz Ku/C-bands: ALT_COR_SWH_01 algorithm |
ADDITIONAL INFORMATION |
None |
PARAMETERS RELATED |
Ocean significant wave height validity flag (swh_ocean_qual_[x1]_[x2]). Flag indicating the use or not of the 20 Hz estimate of the ocean significant wave height in the computation of 1 Hz estimate. |
PARAMETER DETAILED DESCRIPTION |
ESA's Global Land and Ocean Mission for GMES Operational Services |