3.2.2 Despeckle

SAR images are generally corrupted by speckle noise. To suppress speckle and improve the radar image analysis lots of filtering techniques have been proposed. The module implements to well-known despeckle methods: Frost, Lee, Gamma-MAP and Kuan.

Figure (?? shows an extract of a SLC Sentinel1 image, band VV, taken over Cape Verde and the result of the Gamma filter. The following commands were used to produce the despeckled extract :

First, the original image is converted into an intensity one (real part corresponds to band 1, and imaginary part to band 2):

otbcli_BandMath -il S1-VV-extract.tif  
                -exp im1b1^2+im1b2^2  
                -out S1-VV-extract-int.tif

Then the intensity image is despeckled with the Gamma-MAP filter :

otbcli_Despeckle -in S1-VV-extract-int.tif  
                 -filter.gammamap.rad 5  
                 -filter.gammamap.nblooks 1  
                 -out S1-VV-despeckled-extract.tif

The produced images were then rescaled to intensities ranging from 0 to 255 in order to be displayed.


PIC PIC

Figure 3.6: Intensity image from a SLC-VV Sentinel1 image and result of Gamma filter.