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Purpose

 

Images obtained from coherent sensors such as SAR (or Laser) system are characterized by speckle, This is a spatially random multiplicative noise due to coherent superposition of multiple backscatter sources within a SAR resolution element. In other words, speckle is a statistical fluctuation associated with the radar reflectivity of each pixel a scene. A first step to reduce the speckle - at the expense of  spatial resolution - is usually performed during the multi-looking, where range and/or azimuth resolution cells are averaged.

 

Technical Note

 

De Grandi Filter

It has to be pointed out that this multi-temporal filtering is based on the assumption that the same resolution element on the ground is illuminated by the radar beam in the same way, and corresponds to the same co-ordinates in the image plane (sampled signal) in all images of the time series. In other words the SAR geometry is the same for all acquisitions. The reflectivity can of course change from one time to the next due to a change in the dielectric and geometrical properties of the elementary scatters, but should not change due to a different position of the resolution element with respect to the radar. Therefore proper spatial coregistration of the SAR images in the time series is condition sine qua non and of paramount importance.

 

The Coregistration step must be performed prior the execution of this filter. Input data must be in the satellite view geometry; geocoded (_geo) data are not admitted.

 

The filter works in a combined time-space domain. Each element in homogeneous areas with developed speckle is averaged with corresponding uncorrelated elements  in the time-series. The mean values of the probability distribution function of each instance in the averaged series is adjusted to keep track of changes in reflectivity. The adjustment is performed in space by estimation in a diagonal wavelet basis  of the local mean backscatter values in each data set. Since the wavelet based estimator preserves structures in the image (such as edges and point targets), these structures (and changes thereof)  are also preserved (and denoised) by the time domain averaging.

In the DualPol case, the number of channels used in the LMMSE filtering will be doubled with respect to the Single Pol version since both polarizations for each date will be used.

 

The current filter is a variant, taylored for dual-pol processing, of the one proposed in:

G. F. De Grandi, M. Leysen, J. S. Lee, and D. Schuler, “Radar reflectivity estimation using multiple SAR scenes of the same target: Technique and applications,” in Proc. IEEE Int. Remote Sens. Sci. Vis. Sustain. Develop. Geosci. Remote Sens. (IGARSS’97), Aug. 3–8, 1997, vol. 2, pp. 1047–1050.

 

 

Input Files

 

Input file list

Input file names of coregistered (_pwr, _rsp) data. This file list is mandatory.

Note: The order of the files in the list must be, for the same date, Co-Pol followed by Cross-Pol.

 

Parameters - Principal Parameters

 

-Make Differential Ponderation

If false, the process will be carried only on the maximum common area. NaN will be propagated throughout the time series.

If true, the LMMSE step will be executed in a differential ponderation fashion. NaN will not be propagated.

 

 

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 file list

Output file list of the filtered data. This file list is mandatory.

 

_fil        

Filtered Intensity image and associated header files (.sml, .hdr).

 

_meta        

It allows to load the processing results as a single file.

 

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

 

G. F. De Grandi, M. Leysen, J. S. Lee, and D. Schuler, “Radar reflectivity estimation using multiple SAR scenes of the same target: Technique and applications,” in Proc. IEEE Int. Remote Sens. Sci. Vis. Sustain. Develop. Geosci. Remote Sens. (IGARSS’97), Aug. 3–8, 1997, vol. 2, pp. 1047–1050.