Ice sheet re-tracking estimates - Sentinel-3 Altimetry Technical Guide - Sentinel Online
Two different retrackers have been implemented in the Level-2 processor when operating over ice-sheets:
- LRM: Maximum Likelihood Estimation of the 4th order (MLE4) is used to perform a fitting of the waveform with a 4-th parametric model (amplitude, arrival time/epoch, rise time/leading edge, and trailing edge decay).
- SAR: The method is that used for waveforms received in the SARin degraded case for the CryoSat-2 mission, where the phase and coherence information is unavailable. The retracking algorithm has been designed to exploit least squares fitting of a semi-analytical model of the echo. The echo model is a modified gaussian form. It corresponds to a six parametrizable function with 5-section modelling.
The main output of these two retrackers annotated in the Level-2 product are:
- corrected "ice sheet" altimeter range
- corrected "ice sheet" backscatter coefficient
- elevation of echoing points
PARAMETER |
Corrected Ice-Sheet Elevation of Echoing Points |
NETCDF NAME |
range_ice_[x1]_[x2] |
DESCRIPTION |
LRM mode: ice-sheet retracking using the ALT_RET_ICE_04 algorithm. |
UNITS |
10-4 m. An offset of 700 000 m to be added to the value read from the netCDF file. |
DATA SET AVAILABILITY |
Reduced: None |
OPERATING MODE AVAILABILITY |
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 |
Corrected Ice-Sheet Altimeter Range |
NETCDF NAME |
range_ice_sheet_[x1]_[x2] |
DESCRIPTION |
LRM mode: Ice-sheet re-tracking using the ALT_RET_ICE_04 algorithm. |
UNITS |
10-4 m. An offset of 700 000 m to be added to the value read from the netCDF file. |
DATA SET AVAILABILITY |
Reduced: None |
OPERATING MODE AVAILABILITY |
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 |