Minimize Geophysical Corrections

The geophysical corrections computed at Level-2 processing are:

  • Model dry tropospheric corrections (zero and measurement altitudes) (mod_dry_tropo_cor_zero_altitude_[x1]_[x2]): computed  from 3d meteorological fields at zero altitude, at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. A dry tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for dry tropospheric range delays of the radar pulse. For (mod_dry_tropo_cor_meas_altitude_[x1]_[x2])) computed from 3d meteorological fields at measurement altitude, at the altimeter time-tag. A dry tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for dry tropospheric range delays of the radar pulse.
  • Model wet tropospheric corrections (zero and measurement altitudes) (mod_wet_tropo_cor_zero_altitude_[x1]_[x2]): computed from 3d meteorological fields at zero altitude, at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. A wet tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for wet tropospheric range delays of the radar pulse. For (mod_wet_tropo_cor_meas_altitude_[x1]_[x2])): computed from 3d meteorological fields at measurement altitude, at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. A wet tropospheric correction must be added (negative value) to the instrument range to correct this range measurment for wet tropospheric range delays of the radar pulse.
  • Composite wet tropospheric correction (comp_wet_tropo_cor_[x1]_[x2]): computed at the altimeter time-tag from both radiometer and model corrections over areas where the radiometer wet troposphere correction is missing or supposed as invalid due to the proximity of emerged lands, coastal areas and/or radiometer gaps in open oceans. A wet tropospheric correction must be added (negative value) to the instrument range to correct this range measurement fro wet tropospheric range delays of the radar pulse.
  • Radiometer wet tropospheric correction (rad_wet_tropo_cor_[x1]_[x2]): a wet tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for wet tropospheric range delays of the radar pulse. This correction is valid over ocean surfaces only.
  • Radiometer wet tropospheric correction using SST and Gamma (rad_wet_tropo_cor_[x1]_[x2]): computed at the altimeter time-tag from the radiometer brightness temperatures, the Ku-band backscatter coefficient, the sea surface temperature and the lapse rate (decreasing rate of the atmosphere temperature with altitude). A wet tropospheric correction must be added (negative value) to the instrumetn range to correct this range measurement for wet tropospheric range delays of the radar pulse.
  • Altimeter ionospheric correction on Ku band (iono_cor_alt_[x1]_[x2]): an ionospheric correction must be added (negative value) to the instrument range to correct this range measurement for ionospheric range delays of the radar pulse. This correction is valid over ocean surfaces only.
  • GIM-derived ionospheric correction on Ku band (iono_cor_gim_[x1]_[x2]): an ionospheric correction must be added (negative value) to the instrument range to correct this range measurement to ionospheric range delays of the radar pulse.
  • Sea state bias correction (sea_state_bias_[x1]_[x2]): a sea state bias correction must be added (negative value) to the instrument range to correct this range measurement for sea state delays of the radar pulse.
  • Atmospheric attenuation correction (atm_cor_sig0_[x1]_[x2])
  • Mean sea surface height above reference ellipsoid (solution 1) (mean_sea_surf_sol1_[x1]_[x2])
  • Mean sea surface height accuracy (solution 1) (mean_sea_surf_sol1_acc_[x1]_[x2])
  • Mean sea surface height above reference ellipsoid (solution 2) (mean_sea_surf_sol2_[x1]_[x2])
  • Mean dynamic topography above goid (mean_dyn_topo_[x1]_[x2])
  • Mean dynamic topography accuracy (mean dyn_topo_acc_[x1]_[x2])
  • Geoid height (geoid_[x1]_[x2]): computed from the geoid model with a correction to refer the value to the mean tide system i.e. includes the permanent tide (zero frequency).
  • Ocean depth / land elevation (odle_[x1]_[x2])
  • Inverted barometer height correction (inv_bar_cor_[x1]_[x2]): computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag.
  • High frequency fluctuations of the sea surface topography (hf_fluct_cor_[x1]_^[x2]): provided as a correction to the inverted barometer correction (inv_bar_cor_[x1]_[x2]).
  • Geocentric ocean tide height (GOT model) (ocean_tide_sol1_[x1]_[x2]): Solution 1 corresponds to GOT4.8 model. Includes the corresponding loading tide (load_tide_sol1_[x1]_[x2]) and equilibrium long-period ocean tide height (ocean_tide_eq_[x1]_[x2]). The permanent tide (zero frequency) is not included in this parameter because it is included in the geoid and mean sea surface (geoid_[x1]_[x2]), mean_sea_surf_sol1_[x1]_[x2]).
  • Geocentric ocean tide height (FES model) (ocean_tide_sol2_[x1]_[x2]): Solution 2 corresponds to FES2004 model. Includes the corresponding loading tide (load_tide_sol2_[x1]_[x2]) and equilibrium long-period ocean tide height (ocean_tide_eq_[x1]_[x2]). The permanent tide (zero frequency) is not included in this parameter because it is included in the geoid and mean sea surface (geoid_[x1]_[x2], mean_sea_surf_sol1_[x1]_[x2]).
  • Equilibrium long period ocean tide height (ocean_tide_eq_[x1]_[x2]): this value has already been added to the two geocentric ocean tide height values recorded in the product (ocean_tide_sol1_[x1]_[x2] and ocean_tide_sol2_[x1]_[x2]). The permanent tide (zero frequency) is not included in this parameter because it is included in the geoid and mean sea surface (geod_[x1]_[x2], mean_sea_surf_sol1_[x1]_[x2]).
  • Non-equilibrium long period ocean tide height (ocean_tide_non_eq_[x1]_[x2]): this parameter is computed as a correction to the parameter ocean_tide_eq_[x1]_[x2]. This value can be added to ocean_tide_eq_[x1]_[x2] (or ocean_tide_sol1_[x1]_[x2], ocean_tide_sol2_[x1]_[x2]) so that the resulting value models the total non equilibrium ocean tide height.
  • Load tide height (GOT model) (load_tide_sol1_[x1]_[x2]): this value has already been added to the corresponding ocean tide height value recorded in the product (ocean_tide_sol1_[x1]_[x2]).
  • Load tide height (FES model) (load_tide_sol2_[x1]_[x2]): this value has already been added to the corresponding ocean tide height value recorded in the product (ocean_tide_sol2_[x1]_[x2]).
  • Solid earth tide height (solid_earth_tide_[x1]_[x2]): calculated using Cartwright and Tayler tables and consisting of the second and third degree constituents. The permanent tide (zero frequency) is not included.
  • Geocentric pole tide height (pole_tide_[x1]_[x2])
  • Rain rate (rain_rate_[x1]_[x2])
  • Rain attenuation (rain_att_[x1]_[x2])
  • Sea-ice concentration (sea_ice_concentration_[x1]_[x2])
  • Snow density (snow_density_[x1]_[x2])
  • Snow depth (snow_depth_[x1]_[x2])

 

 

PARAMETER

Geophysical Corrections Applied to Backscatter Coefficient: Atmospheric Attenuation Correction

NETCDF NAME

atm_cor_sig0_[x1]_[x2]
[x1]: 1 Hz or 20 Hz data rates
[x2]: Ku-band or C-band

DESCRIPTION

The RAD_PHY_ATT_01 algorithm computes the atmospheric attenuation correction. The Ku-band and C-band backscatter coefficient two-way atmospheric attenuations are computed from the MWR (Microwave Radiometer) 23.8 GHz and 36.5 GHz brightness temperatures (interpolated at the SRAL time tag) and from the Ku-band sigma0.

UNITS

10-2 dB

DATA SET AVAILABILITY

Reduced: none
Standard: 1 Hz Ku and C-bands
Enhanced: 1 Hz Ku and C-bands

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: RAD_PHY_ATT_01 algorithm
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

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

Table 1. Atmospheric

 
 

PARAMETER

Geophysical Corrections Applied to Altimeter Range:Sea State Bias (SSB) Correction

NETCDF NAME

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

DESCRIPTION

The ALT_COR_RAN_04 algorithm computes the sea state bias. The sea state bias is the difference between the apparent sea level as "seen" by an altimeter and the actual mean sea level. A sea state bias correction must be added (negative value) to the instrument range to correct this range measurement for sea state delays of the radar pulse.

UNITS

10-4 m

DATA SET AVAILABILITY

Reduced: 1 Hz Ku-band
Standard: 1 Hz Ku/C-bands only
Enhanced: 1 Hz Ku/C-bands only

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: ALT_COR_RAN_04 algorithm
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

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

Table 2. Sea state bias

 

 

PARAMETER

Geophysical Corrections Applied to Altimeter Range:Ionospheric Correction

NETCDF NAME

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

DESCRIPTION

The ALT_COR_RAN_05 algorithm computes ionospheric corrections using the dual-frequency (Ku and C-bands) measurements.

UNITS

10-4 m

DATA SET AVAILABILITY

Reduced: 1 Hz Ku-band
Standard: 1/20 Hz Ku-band only
Enhanced: 1/20 Hz Ku-band only

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: ALT_COR_RAN_05 algorithm
20 Hz Ku-band: ALT_COR_RAN_05 algorithm
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

Ionospheric correction derived from GIM (Global Ionospheric Maps) model(iono_cor_gim_[x1]_[x2])

PARAMETER DETAILED DESCRIPTION

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

Table 3. Ionospheric

 

 

PARAMETER

Mean Sea Surface Height

NETCDF NAME

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

DESCRIPTION

The GEN_ENV_MSS_01 algorithm computes Mean Sea Surface (MSS) height above the reference ellipsoid. The model used is CLS01.

UNITS

10-4 m

DATA SET AVAILABILITY

Reduced: 1 Hz
Standard: 1 Hz Ku/C-bands and 20 Hz Ku-band
Enhanced: 1 Hz Ku/C-bands and 20 Hz Ku-band

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: GEN_ENV_MSS_01 algorithm, 20 Hz Ku-band: GEN_ENV_MSS_01 algorithm, 20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

Mean sea surface height accuracy (mean_sea_surf_acc_[x1]_[x2])

PARAMETER DETAILED DESCRIPTION

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

Table 4. Mean sea surface height


 

PARAMETER

Ocean Depth / Land Elevation

NETCDF NAME

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

DESCRIPTION

The GEN_ENV_BAT_01 algorithm computes the ocean depth or land elevation from a bathymetry / topography file. The model used is the global digital elevation model MACESS. If the surface type of the altimeter measurement is set to "open ocean or semi-enclosed seas", only grid points having negative altitude are used in the interpolation. If no grid points with negative altitude are found, the four grid points having positive altitude are used. If the altimeter measurement is set to "enclosed seas or lakes", "continental ice" or "land", all grid points are used in the interpolation regardless of their altitude.

UNITS

10-4 m

DATA SET AVAILABILITY

Reduced: 1 Hz
Standard: 1 Hz
Enhanced: 1 Hz

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: GEN_ENV_BAT_01 algorithm
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

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

Table 5. Ocean depth - land elevation

 
 

PARAMETER

Rain Rate and Rain Attenuation

NETCDF NAME

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

DESCRIPTION

The ALT_PHY_GEN_02 algorithm computes the rain attenuation (rain_att_[x1]_[x2]). Rain attenuation is the difference between the expected main band backscatter coefficient and the measured main band backscatter coefficient.
The ALT_PHY_GEN_03 algorithm computes the rain rate (rain_rate_[x1]_[x2]). Rain rate is computed from the freezing level and rain attenuation using the Marshal-Palmer relation. The freezing level is inferred by the inversion of the radiometer brightness temperatures or from seasonal maps of freezing level, if the inversion process fails.

UNITS

Rain attenuation: 10-2 dB
Rain rate: 10-2 mm/h

DATA SET AVAILABILITY

Reduced: none
Standard: 1 Hz
Enhanced: 1 Hz

OPERATING MODE AVAILABILITY

LRM only

DATA ORIGIN

1 Hz Ku/C-bands: ALT_PHY_GEN_02 and ALT_PHY_GEN_03 algorithms
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

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

Table 6. Rain rate

 
 

PARAMETER

Tide Height Corrections

NETCDF NAME

ocean_tide_sol1_[x1]_[x2] (GOT model)
ocean_tide_sol2_[x1]_[x2] (FES model)
[x1]: 1 Hz or 20 Hz data rates
[x2]: Ku-band or C-band

DESCRIPTION

The GEN_ENV_TID_04 algorithm computes the tide height (ocean_tide_sol1_[x1]_[x2]) using the GOT00.2 model. It includes the corresponding loading tide (load_tide_sol1_[x1]_[x2]) and equilibrium long-period ocean tide height (ocean_tide_eq_[x1]_[x2]).
The GEN_ENV_TID_03 algorithm computes the tide height (ocean_tide_sol2_[x1]_[x2]) using the FES2004 model. It includes the corresponding loading tide (load_tide_sol2_[x1]_[x2]) and equilibrium long-period ocean tide height (ocean_tide_eq_[x1]_[x2]). The permanent tide (zero frequency) is not included in both parameters (ocean_tide_sol1_[x1]_[x2] and ocean_tide_sol2_[x1]_[x2]) because it is included in the geoid and mean sea surface (geoid_[x1]_[x2], mean_sea_surf_[x1]_[x2]).

UNITS

10-4 m

DATA SET AVAILABILITY

Reduced: 1 Hz (GOT model only)
Standard: 1 Hz
Enhanced: 1 Hz

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: GEN_ENV_TID_03 and GEN_ENV_TID_04 algorithms
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

Non-equilibrium long period ocean tide height (ocean_tide_non_eq_[x1]_[x2]). This parameter is computed as a correction to equilibrium long period ocean tide. This value can be added to equilibrium long period ocean tide so that the resulting value models the total non-equilibrium ocean tide height.
Solid earth tide height (solid_earth_tide_[x1]_[x2]). It is calculated using Cartwright and Tayler tables and consisting of the second and third degree constituents. The permanent tide (zero frequency) is not included.
Geocentric pole tide height (pole_tide_[x1]_[x2]). Sea surface height due to pole tide.

PARAMETER DETAILED DESCRIPTION

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

Table 7. Tide heights

 

 

PARAMETER

Snow Density and Snow Depth

NETCDF NAME

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

DESCRIPTION

Geo CFI and ALT_COR_RAN_06 algorithms compute snow depth, extracting it from the snow depth climatology auxiliary file and performing a bilinear interpolation.

UNITS

Snow density: kg/m-3
Snow depth: 10-4 m

DATA SET AVAILABILITY

Reduced: none
Standard: 20 Hz Ku-band only
Enhanced: 20 Hz Ku-band only

OPERATING MODE AVAILABILITY

SAR only

DATA ORIGIN

1 Hz Ku/C-bands: none
20 Hz Ku-band: Geo CFI and ALT_COR_RAN_06 algorithms
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

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

Table 8. Snow density and depth

 

 

PARAMETER

Geophysical Corrections Applied to Altimeter Range: Wet and Dry Tropospheric Correction

NETCDF NAME

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

DESCRIPTION

The GEN_COR_RAN_01 algorithm computes the dry tropospheric correction at measurement altitude from meteorological models. A dry tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for dry tropospheric range delays of the radar pulse.
The RAD_PHY_GEN_02 algorithm computes from the microwave radiometer brightness temperatures, the Ku-band backscattering coefficient, the Sea Surface Temperature (SST) and the lapse rate (decreasing rate of the atmosphere temperature with altitude). Wet tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for wet tropospheric range delays of the radar pulse.

UNITS

10-4 meters

DATA SET AVAILABILITY

Reduced: 1 Hz (dry tropospheric) and none (wet tropospheric)
Standard: 1 Hz only
Enhanced: 1 Hz only

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: GEN_COR_RAN_01 and RAD_PHY_GEN_02 algorithms
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

Composite web tropospheric correction (comp_wet_tropo_cor_[x1]_[x2]) is based on both radiometer and model corrections over areas where the radiometer wet troposphere correction is missing or supposed as invalid due to the proximity of emerged lands: coastal areas and/or radiometer gaps in open oceans.
Dry tropospheric correction at zero altitude (mod_dry_tropo_cor_zero_altitude_[x1]_[x2]).
Wet tropospheric correction at both zero and measurement altitude (mod_wet_tropo_cor_zero_altitude_[x1]_[x2] and mod_wet_tropo_cor_meas_altitude_[x1]_[x2]).
Wet tropospheric correction computed from the MWR 23.8 GHz and 36.5 GHz brightness temperatures (interpolated at the SRAL time-tag) and from the Ku-band sigma0 (rad_wet_tropo_cor_[x1]_[x2]).

PARAMETER DETAILED DESCRIPTION

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

Table 9. Tropospheric

 

 

PARAMETER

Sea-Ice Concentration

NETCDF NAME

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

DESCRIPTION

Geo CFI and ALT_COR_RAN_06 algorithms compute the sea-ice concentration, extracting it from a sea-ice auxiliary file and performing a bilinear interpolation

UNITS

10-2 %

DATA SET AVAILABILITY

Reduced: none
Standard: 20 Hz Ku-band only
Enhanced: 20 Hz Ku-band only

OPERATING MODE AVAILABILITY

SAR only

DATA ORIGIN

1 Hz Ku/C-bands: none
20 Hz Ku-band: Geo CFI and ALT_COR_RAN_06 algorithms
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

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

Table 10. Sea-ice concentration

 

 

PARAMETER

Mean Dynamic Topography

NETCDF NAME

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

DESCRIPTION

The GEN_ENV_MDT_01 algorithm computes Mean Dynamic Topography (MDT) above geoid. The model used is CLS RIO 05.

UNITS

10-4 m

DATA SET AVAILABILITY

Reduced: 1 Hz
Standard: 1 Hz
Enhanced: 1 Hz

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: GEN_ENV_MDT_01 algorithm
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

Mean dynamic topography accuracy (mean_dyn_topo_acc_[x1]_[x2])

PARAMETER DETAILED DESCRIPTION

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

Table 11. Mean dynamic topography

 

 

PARAMETER

Geoid height

NETCDF NAME

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

DESCRIPTION

The GEN_ENV_GEO_01 algorithm computes the geoid height above the reference ellipsoid. The model used is EGM96.

UNITS

10-4 m

DATA SET AVAILABILITY

Reduced: none
Standard: 1 Hz
Enhanced: 1 Hz

OPERATING MODE AVAILABILITY

LRM and SAR

DATA ORIGIN

1 Hz Ku/C-bands: GEN_ENV_GEO_01 algorithm
20 Hz Ku-band: none
20 Hz C-band: none

ADDITIONAL INFORMATION

None

PARAMETERS RELATED

None

PARAMETER DETAILED DESCRIPTION

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

Table 12. Geoid height