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Purpose

 

Water vapour data contained in ENVISAT MERIS or GACOS . MERIS and GACOS standard products must be previously imported, note that MERIS works with ENVISAT ASAR products only. It is important to point out that the MERIS and GACOS master and slave data must have been acquired simultaneously to the corresponding SAR acquisitions.

 

Technical Note

 

The layers of master and slave data, containing the water vapor related parameters, are used to compute the phase delay of the corresponding acquisitions. The calculated phase delay difference is subtracted to the input flattened (and possibly filtered) interferogram.

 

It must be noted that cloud covered data should not be used for this purpose. Isolated cloudy pixels are masked out by means of an available mask provided with the input data, in the MERIS case the mask is generated starting from the input layers of "Cloud Mask", "Reflectance" and "Pressure" (all provided with the original standard product).

 

- Data Interpolation is intended to assign a specific value to the dummy/masked (NaN) pixels, which typically correspond to the clouds. The "Relax Interpolation" model is represented by a soft surface, which is adapted to the dummy surrounding area. The algorithm, which is based on the solution of the heat transfer equation (Poisson equation), uses known water vapor values to reconstruct at the best the masked areas. It must be noted that isolated dummy pixels are better interpolated using an "Interpolation Window", which can be associated with the "Relax Interpolation".

 

- Mean Filter is used in order to smooth small atmospheric changes (e.g. isolated clouds).

 

 

Input Files

 

Interferogram file

File name of the previously generated interferogram (_dint or _fint). This file is mandatory.

 

Slant Range Digital Elevation Model file

Name of the Digital Elevation Model in slant range geometry (_srdem). This file is mandatory.

 

Optional Files

 

Optional Master Water Vapour File

File name of the master water vapour data or data file list (_filename_list.txt; *_bil). This file is mandatory only when the MERIS or GACOS sensor type is used.

 

Optional Slave Water Vapour File

File name of the slave water vapour data or data file list (_filename_list.txt; *_bil). This file is mandatory only when the MERIS or GACOS sensor type is used.

 

Unwrapped Phase File

Name of the unwrapped phase (_upha). This file is mandatory only when the Atmosphere Height Correlation Flag is selected.

 

Parameters - Principal Parameters

 

Atmosphere External Sensors

By inserting this optional list, the software removes the atmosphere artefacts from the filtered interferogram stack using external sensors such as GACOS and MERIS (only for ENVISAT data).

 

Atmosphere Height Correlation Flag

By selecting this flag, the algorithm estimates and removes the height-related component of the atmosphere from each interferogram, using a the “Height Correlation Window Size [m]” (Atmosphere section) parameter to define the size of the filter. To enable this flag is mandatory to upload an _upha file within the Unwrapped Phase File filed.

 

Parameters - Global

 

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

 

Parameters - Other Parameters

 

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

 

Output Files

 

Output Root Name

Name of the output root. This file is mandatory.

 

_corr_dint/fint

Corrected interferogram with the associated header files (.sml, .hdr).

 

_corr_mask

MERIS masked master and slave data, in the original image geometry, with the associated header files (.sml, .hdr).

 

_corr_atm

Atmospheric phase delay, in slant range SAR master image geometry, with the associated header files (.sml, .hdr).

 

Details specific to the Units of Measure and Nomenclature of the output products can be found in the Data Format section.

 

General Functions

 

Exec

The processing step is executed.

 

Store Batch        

The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.

 

Close        

The window will be closed.

 

Help

Specific help document section.

 

 

Specific Function(s)

 

None.

 

References

 

Z. Li, E.J. Fielding, P. Cross, and J.-P. Muller, ”Interferometric synthetic aperture radar atmospheric correction: MEdium Resolution Imaging Spectrometer and Advanced Synthetic Aperture Radar integration”, Geophysical Research Letters, 33: L06816, 2006.

 

R. Jolivet, R. Grandin, C. Lasserre, M. P. Doin, G. Peltzer, "Systematic InSAR tropospheric phase delay corrections from global meteorological reanalysis data", Geophysical Research Letters, Vol. 38, No. 17., 2011.