Product Description

• UPorto GPD+ Wet Tropospheric Correction

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• UPorto GPD+ for all missions

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

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; doi: 10.1016/j.rse.2015.07.023