Minimize OCOG re-tracking

The Offset Centre of Gravity (OCOG) re-tracker is a heritage of the ice-1 re-tracker implemented in both ENVISAT and CryoSat-2 missions. It is an empirical-based algorithm used in LRM mode for ice surfaces and in SAR mode for sea-ice margins.

This method is based on the OCOG and requires form the estimation of the waveform amplitude as it is using a threshold-based approach to infer the epoch. Then, OCOG amplitude is estimated.

The retracker correction is computed as the difference between the OCOG retracked bin and the nominal tracking point. This is finally added to the estimated range to the surface (through the measured window delay) in order to obtain the corrected range.

The main output of these two retrackers annoted in the Level-2 products are:

  • corrected OCOG altimeter range
  • corrected OCOG backscatter coefficient
 

PARAMETER

Corrected OCOG Altimeter Range

NETCDF NAME

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

DESCRIPTION

LRM mode: OCOG retracking using ALT_RET_ICE_01 algorithm.
SAR mode : OCOG retracking using ALT_RET_ICE_01 algorithm.
A standard Offset Centre Of Gravity (OCOG) retracking (called ice-1) is performed on the power waveform. The instrumental corrections already included are: USO drift correction (uso_cor_[x1]_[x2]), internal path correction (int_path_cor_[x1]_[x2]), distance antenna-COG (cog_cor_[x1]_x2]).

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

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: none
20 Hz Ku-band: ALT_RET_ICE_01 algorithm
20 Hz C-band: ALT_RET_ICE_01 algorithm

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

ESA's Global Land and Ocean Mission for GMES Operational Services

Table 1. OCOG altimeter range

 
 

PARAMETER

Corrected OCOG Backscatter Coefficient

NETCDF NAME

sig0_ocog_[x1]_[x2]
[x1]: 1 Hz or 20 Hz data rates
[x2]: Ku-band or C-band

DESCRIPTION

LRM mode: OCOG re-tracking
SAR mode : OCOG 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_03 algorithm computes the backscatter coefficient for LRM mode. The ALT_PHY_BAC_02 algorithm computes the backscatter coefficient for SAR mode.

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 and SAR

DATA ORIGIN

1 Hz Ku/C-bands: None
20 Hz Ku-band: ALT_PHY_BAC_02 and ALT_PHY_BAC_03 algorithms
20 Hz C-band: ALT_PHY_BAC_02 and ALT_PHY_BAC_03 algorithms

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

ESA's Global Land and Ocean Mission for GMES Operational Services

Table 2. OCOG backscatter coefficient