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2.9.3 Level 2 processing

The auxiliary files to be used solely for the RA2/MWR L2 processing are the following:

RA2_IOC_AX (Model ionospheric coefficients file)

This file contains the values of the polynomial coefficients to be used in the computation of the ionospheric correction from the Bent model in the FDGDR processing. There are two sets of coefficients in every record: the first set of coefficients is related to the critical frequency and the second set to the ratio of maximum usable frequency to the critical frequency. This file has to be updated typically once a year, since these coefficients cover one year (one record per month). This file, used only for NRT processing, has not been updated yet.

In the off line processing, the ionospheric correction is computed using daily TEC maps coming from a different (non-PDS formatted) auxiliary file, that can be distributed only by the AVISO catalogue entity.

RA2_MSS_AX (Mean Sea Surface)

This file contains the values of the mean sea surface heights.

The MSS model used for the calculation of the sea heights has been updated since launch. Currently the CLS01 model is used.

The values are recorded on a regular grid with 2 minutes resolution in longitude and latitude. This file is used in the FDGDR, IGDR and GDR processing.

RA2_SOL_AX (Solar activity data file)

The data in this file, containing the 12 month running average of the sunspot numbers (solar activity indexes), is used to compute the Bent model ionospheric correction in NRT. The solar activity indexes neededfor the OFL DORIS iono correction are extracted from a different external file (daily DORIS TEC maps).

Predicted solar activity data is used for NRT while measured data is used for the off line processing. The data in this file is updated approx. once per month by a dedicated IECF function.

RA2_POL_AX (Pole location position data file)

The data contained in this file is related to the position of the pole, needed to calculate the geocentric pole tide height. The predicted pole data is used for NRT processing, while the analysed data is used for off line. The polar motion data in this file is updated twice per week by a dedicated IECF function.

RA2_PLA_AX (Platform data file)

This file contains the center of mass correction (i.e. distance between antenna phase center and the center of gravity of the satellite) that is applied during the (NRT and off line) level 2 processing to the retracked altimeter range. The CoM - antenna phase center distance is obtained only from the projection on the z-axis, since the x-axis component is negligible. The file is updated every time there is a consumption of satellite fuel due to a manoeuvre. In NRT this is done automatically by a dedicated IECF function.

In OFL, the CoM-antenna data, coming also from the FOS file, is stored in a different aux. file.

RA2_SOI_AX (Ocean/Ice 2 configuration system file)

This file contains the processing parameters (constants, thresholds, tables) for the ocean/ice2 processing. These parameters are used for NRT and off line processing.The file has been updated during Commissioning Phase in the frame of the Level 2 algorithms verification group activities.

RA2_ICT_AX (Ice1/ sea ice Configuration system file)

This file contains the processing parameters (constants, thresholds, tables) for the ice 1/sea ice processing. These parameters are used for off line processing. The file has been updated during Commissioning Phase in the frame of the Level 2 algorithms verification group activities

RA2_SSB_AX (Sea State Bias table file)

This file contains the values of the sea state bias corrections for the Ku and S bands, to be used for NRT and off line processing. It is a double input table depending on significant waveheight and windspeed. The SWH coverage is from 0 t o12 m, with a resolution of 0.25 m, while the coverage for windspeed is from 0 to 25 m/s with a resolution of 0.25 m/s.

This file has been updated with a new one that is based on the analysis of ten cycles (cycle 25 to 35), using residuals relative to a mean sea surface and applying the non parametric estimation technique

RA2_DIP_AX (Modified Dip Map file)

This file contains the values of the modified magnetic dip used in the computation of the ionospheric correction from the Bent model in the NRT processing. The values are recorded on a regular grid with 2 degrees resolution in longitude and latitude.

RA2_SET_AX (Cartwright Amplitudes file)

This file contains the values of Cartwright amplitudes of the tidal constituents harmonic coefficients and amplitudes which are used for the computation of the solid earth tide height in the NRT and off line processing. Each record contains six harmonic coefficients and the amplitude for each potential term of the second and third order.

No update of this file has been done during Commissioning Phase.

RA2_OT1_AX (Coefficient map for the ocean tide calculation - solution 1)

This file contains the values of the harmonic coefficients for the height of the principal tide waves of the GOT00.2 model. They are used for the computation of the non-equilibrium ocean tide height in the NRT and off line processing. The values are recorded on a regular grid with 0.5 deg resolution in longitude and latitude. Eight values of the A1 harmonic coefficients and eight values of the A2 harmonic coefficients are recorded at each grid point.

RA2_OT2_AX (Coefficient map for the ocean tide calculation - solution 2)

This file contains the values of the harmonic coefficients for the height of the principal tide waves of FES2002 model for NRT and FES2004 for Offline processing. They are used for the computation of the non-equilibrium ocean tide height. The values are recorded on a regular grid with 0.25 deg resolution for NRT, and 0.125 deg for OFL, in latitude and longitude. Eight values of the A1 harmonic coefficients and eight values of the A2 harmonic coefficients are recorded at each grid point.

RA2_TLG_AX (Coefficients map for the tidal loading calculation - solution 1)

This file contains the values of the harmonic coefficients for the height principal tide waves of the GOT00.2 model. They are used for the computation of the height of the tidal loading effect in the NRT and off line processing. The values are recorded on a regular grid with 0.5 deg resolution in latitude and longitude. Eight values of the B1 harmonic coefficients and eight values of the B2 harmonic coefficients are recorded at each grid point.

RA2_TLD_AX (Coefficients map for the tidal loading calculation - solution 2)

This file contains the values of the harmonic coefficients for the height principal tide waves computed from the Francis and Mazzega's method, using the solution 2 ocean tide model as input. They are used for the computation of the height of the tidal loading effect in the NRT and off line processing. The values are recorded on a regular grid with 0.25 deg resolution in latitude and longitude. Eight values of the B1 harmonic coefficients and eight values of the B2 harmonic coefficients are recorded at each grid point.

RA2_GEO_AX (Geoid height map)

This file contains the values of the geoid heights, EGM96, during NRT and off line processing. The values are recorded on a regular grid with 0.25 deg resolution in latitude and longitude.

AUX_DEM_AX (Ocean depth/land elevation map)

This ENVISAT wide file contains the values of the ocean depth or land elevation, MACESS model to be used for the NRT processing. The values are recorded on a regular grid with a 5 minutes resolution in longitude and latitude for NRT and with a 2 minutes resolution in longitude and latitude for off line processing.

RA2_SL1_AX (RA-2 slope model for Greenland data file)

This file contains the Greenland slope data to be used in the ice1/sea ice processing in off line processing. The horizontal sampling resolution for this model is 2.5 Km. Each record contains the x and y range slope components.

RA2_SL2_AX (RA-2 slope model for Antarctica data file)

This file contains the Antarctica slope data to be used in the ice1/sea ice processing in off line processing. The horizontal sampling resolution for this model is 5 Km. Each record contains the x and y range slope components.

MWR_LSF_AX (Land/Sea mask map)

This file contains the values of the land/sea flag to be used for the RA2/MWR level 2 NRT and off line processing. The values are recorded on a regular grid with 2 minutes resolution in latitude and longitude. Each value is recorded at each grid point with the following meaning: 0 (oceans or semi-enclosed seas), 1 (enclosed seas or lakes), 2 (continental ice) or 3 (land).

RA2_MET_AX (Altitude of meteorological grid points)

This file contains the altitude of meteorological grid points to be used during the NRT processing. This file contains only one record corresponding to the 360X181 grid points of the meteorological grid found in the predicted meteorological data.

AUX_ECF_AX and AUX_ECA_AX (ECMWF forecast and analysis meteorological data files)

The predicted ECMWF data provided by ECMWF are relative to the prediction of the wet and dry tropospheric corrections, and the 10 m wind vectors. They are used in the NRT processing to compute the wet and dry tropospheric range corrections and the sea state bias correction to be applied on the altimeter measurement. The ECMWF parameters used during the processing are the relative humidity, geopotential, temperature, mean sea level pressure, and U and V components of the 10 m wind vector. The first three parameters are profiles (relative to 21 altitude levels of the meteorological model) while the three latter ones are surface parameters. All of them are provided on a global regular grid, with 1 deg resolution in longitude and latitude.

The meteo data coming from Meteo-France, that uses as input the analysis ECMWF products, is used for the off line processing.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry