Change Detection in Polarimetric SAR Images Using a Geodesic Distance Between Scattering Mechanisms

A novel technique to generate the difference image (DI) in change detection analysis for polarimetric SAR (PolSAR) data is proposed. Unlike the standard methods, viz., band difference or intensity/amplitude ratioing, the proposed technique utilizes the full vector nature of multitemporal PolSAR data. In this data, a pixel is characterized by a <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> Kennaugh matrix. The geodesic distance (GD) on an unit sphere is utilized to define the distance between the Kennaugh matrices of the three elementary targets (trihedral, dihedral, and 45° rotated dihedral about the radar line of sight) producing canonical scattering mechanisms and the observed Kennaugh matrix. Three absolute differences of the GD from respective elementary targets are obtained for time instants <inline-formula> <tex-math notation="LaTeX">$t_{1}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$t_{2}$ </tex-math></inline-formula>. The DI is then the maximum among the three quantities. The proposed technique is applied to two scenes obtained from the L-band UAVSAR data characterizing changes due to urbanization. The principal component analysis with <inline-formula> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula>-means clustering proposed by Celik is used to obtain the binary change map. The proposed differencing method performs better than the single-channel intensity band ratio and the total power ratio for time instants <inline-formula> <tex-math notation="LaTeX">$t_{1}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$t_{2}$ </tex-math></inline-formula>. The detection rate with the proposed technique is 6% and 20% better than the ratio methods for the two data sets, respectively, with the higher <inline-formula> <tex-math notation="LaTeX">$\kappa $ </tex-math></inline-formula> value as a measure of performance evaluation.