Ice re-tracking estimates - Sentinel-3 Altimetry Technical Guide - Sentinel Online
There is a single re-tracker dedicated to LRM mode ice waveforms. This re-tracker method is a heritage of the ice-2 re-tracker (also called ice_erf re-tracker) implemented in both ENVISAT and CryoSat-2 missions. It is a physical-based retracker.
This retracker is based in the Brown model, described by a triple convolution term (flat surface impulse response+height probability density function+radar point target response/PTR), and intended for ice caps studies. The basic idea behind the ice-2 retracker is to detect the waveform edge and then fitting an error function to the leading edge and an exponential decrease to the trailing edge.
The aim of the ice-2 retracker algorithm is to fit the measured waveform with a return power model, according to a Least Square Error (LSE) minimization.
The main outputs of this ice LRM retracker annotated in the Level-2 product are:
- corrected "ice" altimeter range
- corrected "ice" backscatter coefficient
- corrected "ice" leading edge backscatter coefficient (arithmetic average of the waveform samples in a window limited by the beginning of the leading edge and the end of the window used for the slope estimation)
- width of the leading edge
- slope of the first part of the trailing edge (potentially used to identify volume scattering in the signal for ice scenarios and misspointing angles over ocean surfaces)
- slope of the second part of the trailing edge
|
PARAMETER |
Corrected Ice Backscatter Coefficient |
|
NETCDF NAME |
sig0_ice_[x1]_[x2] |
|
DESCRIPTION |
LRM mode: ice re-tracking. |
|
UNITS |
10-2 dB |
|
DATA SET AVAILABILITY |
Reduced: None |
|
OPERATING MODE AVAILABILITY |
LRM |
|
DATA ORIGIN |
1 Hz Ku/C-bands: None |
|
ADDITIONAL INFORMATION |
None |
|
PARAMETERS RELATED |
Corrected ice leading edge backscatter coefficient: sig0_leading_edge_ice_[x1]_[x2] |
|
PARAMETER DETAILED DESCRIPTION |
ESA's Global Land and Ocean Mission for GMES Operational Services |
Table 1. Ice backscatter coefficient
|
PARAMETER |
Ice Width of the Leading Edge |
|
NETCDF NAME |
width_leading_edge_ice_[x1]_[x2] |
|
DESCRIPTION |
LRM mode : ice re-tracking using the ALT_RET_ICE_02 algorithm. The ALT_RET_ICE_02 algorithm is based on the ENVISAT RA-2 ice-2 re-tracker. The aim of the ice-2 re-tracker algorithm is to make the measured waveform coincide with a return power model, according to least square estimators. |
|
UNITS |
10-3 m |
|
DATA SET AVAILABILITY |
Reduced: none |
|
OPERATING MODE AVAILABILITY |
LRM |
|
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 |
Table 2. Width of the leading edge
|
PARAMETER |
Ice Slope of the First and Second Part of the Trailing Edge |
|
NETCDF NAME |
slope_first_trailing_edge_ice_[x1]_[x2] slope_second_trailing_edge_ice_[x1]_[x2] |
|
DESCRIPTION |
LRM mode : Ice re-tracking using ALT_RET_ICE_02 algorithm. |
|
UNITS |
s-1 |
|
DATA SET AVAILABILITY |
Reduced: None |
|
OPERATING MODE AVAILABILITY |
LRM |
|
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 |
Table 3. Slope of the leading edge