Double density wavelet transformation for speckle reduction of SAR images

Discrete wavelet transformations (DWTs) based on oversampled filter banks, proposed by I. W. Selesnick (2001), are used for speckle reduction of SAR images. The oversampled DWT is called double density DWT (DD-DWT) and is based on a single scaling function (lowpass) and two distinct wavelet functions (highpass). The DD-DWT is useful for speckle reduction through its subband images and the speckle reduction is obtained by thresholding the subband-image coefficients of the digitized SAR images. A thresholding method using non-linear functions which are adapted for each selected subband is used in the paper. The non-linear functions are based on sigmoid functions. The denoising method shows great promise for speckle removal and hence can provide good detection performance for SAR based recognition.