Minimize Ice re-tracking

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]
[x1]: 1 Hz or 20 Hz data rates
[x2]: Ku-band or C-band

DESCRIPTION

LRM mode: ice re-tracking.
The instrumental corrections already included are: AGC instrumental errors correction (agc_cor_[x1]_[x2]), internal calibration correction (sig0_cal_[x1]_[x2]). The ALT_PHY_BAC_01 algorithm computes the backscatter coefficient.

UNITS

10-2 dB

DATA SET AVAILABILITY

Reduced: None
Standard: 20 Hz Ku/C bands
Enhanced: 20 Hz Ku/C bands

OPERATING MODE AVAILABILITY

LRM

DATA ORIGIN

1 Hz Ku/C-bands: None
20 Hz Ku-band: ALT_PHY_BAC_01 algorithm
20 Hz C-band: ALT_PHY_BAC_01 algorithm

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]
[x1]: 1 Hz or 20 Hz data rates
[x2]: Ku-band or C-band

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
Standard: 20 Hz Ku/C bands
Enhanced: 20 Hz Ku/C bands

OPERATING MODE AVAILABILITY

LRM

DATA ORIGIN

1 Hz Ku/C-bands: none
20 Hz Ku-band: ALT_RET_ICE_02 algorithm
20 Hz C-band: ALT_RET_ICE_02 algorithm

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]
[x1]: 1 Hz or 20 Hz data rates
[x2]: Ku-band or C-band

DESCRIPTION

LRM mode : Ice re-tracking using 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

s-1

DATA SET AVAILABILITY

Reduced: None
Standard: 20 Hz Ku/C bands
Enhanced: 20 Hz Ku/C bands

OPERATING MODE AVAILABILITY

LRM

DATA ORIGIN

1 Hz Ku/C-bands: None
20 Hz Ku-band: ALT_RET_ICE_02 algorithm
20 Hz C-band: ALT_RET_ICE_02 algorithm

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