GPD+ wet tropospheric correction

GPD+ product description

Altimeters and time coverage

 

The University of Porto  (J. Fernandes) provides a homogeneous wet tropospheric correction for many altimetric missions:

  • ERS-1 — phases a to g, cycles 1 to 156 (RADS convention) or cycles 1 to 53 (AVISO convention), 1991.8–1996.4;
  • ERS-2 — cycles 1 to 167, 1995.4–2011.5,;
  • Envisat — cycles 1 to 113, 2002.4–2012.3;
  • TOPEX/Poseidon — cycles 1 to 481, 1992.7–2005.8;
  • Jason-1 — cycles 1 to 424, 2002.0–2013.5;
  • Jason-2 — cycles 1 to 226, 2008.5–2014.7;
  • Cryosat-2 subcycles 4-86, 2010.7-2016.12;
  • Saral/Altika - cycles 1 to 30, 2013/03/14-2016/01/28;
 

Data access is available through this request form.

 
The products are in NetCDF format and their brief description is found below.  The scientific description of the product is found in two publications:
 
 
 
 

Brief description of the product

 

The correction is provided in netcdf files with the following fields:

 

time_01                     - time of measurement, seconds since 1990-01-01 00:00:00.0 UTC

 

lat_01                            latitude

 

lon_01                           longitude   

 

GPD_wet_tropo_cor_01       wet tropospheric correction (metres)

 

GPD_wet_tropo_cor_qual_01       -validity flag of the wet_GPD estimate:

                         0 - point for which the radiometer correction (rad_wet_tropo_cor)is valid - for these  

                              points wet_GPD=rad_wet_tropo_cor (after applying calibration factors)

                         1 - wet_GPD is a valid estimate

                         2 – there were no observations for this point. In this case wet_GPD equals the model value

                             (ERA Interim or ECMWF Op.) with possible small bias applied.

                         3 - wet_ GPD was outside the interval [-0.5, 0.0], In this case the values -0.5 and 0.0

                              were attributed to the correction.

 

 

Main details of this implementation

 

·       computations include all sea points and first land point in a land/sea transition zone. This avoids loss of points in the coastal regions when time interpolation is required for example for interpolation into 20 Hz points.

·       All missions have been inter-calibrated using the SSMI and SSMI/S sensors as reference, adjusting 3 parameters: scale factor, offset and linear trend. Details are provided on the following   paper:

M. Joana Fernandes and Clara Lázaro, GPD+ Wet Tropospheric Corrections for CryoSat-2 and GFO Altimetry Missions, Remote Sensing 2016, 8(10), 851; doi:10.3390/rs8100851 (http://www.mdpi.com/2072-4292/8/10/851)

 

Another paper is in preparation describing the corrections for all missions except C2 and GFO. For the time being, the corrections should be cited by reference to the previous and to the following paper:

M. Joana Fernandes, Clara Lázaro, Michaël Ablain, Nelson Pires., 2015. Improved wet path delays for all ESA and reference altimetric missions, Remote Sensing of Environment, Volume 169, November 2015, Pages 50-74, ISSN 0034-4257, http://dx.doi.org/10.1016/j.rse.2015.07.023.

 

All questions should be sent to:

Joana Fernandes: mjfernan (with the arobase sign) fc.up.pt

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