Building damage assessment is of great significance to disaster monitoring.Polarimetric Synthetic Aperture Radar (SAR) can record the polarization scattering measurement matrix of ground objects and obtain more abundant ground object information,meaning that they can be used for assessing damage to buildings.In this paper,a new approach is proposed to assess building damage using the Touzi incoherent decomposition and SAR-based characteristics of buildings before and after damage.The March 11th,2011 earthquake that struck the coast of northeast Japan serves as the demonstration of the technique using quad-polarimetric ALOS PALSAR data acquired before and after the disaster.The analysis shows that after the buildings are damaged,there is a clear decrease in the αs1 (the dominant scattering-type magnitude) components and the degree of this reduction corresponds to the degree of building damage.This means that the αs1 components obtained by Touzi decomposition can effectively reflect the degree of building damage.On this basis,a model based on Touzi decomposition was established to evaluate the degree of damage to buildings,and the accuracy of the model was validated using high-resolution optical data acquired before and after the earthquake.The experimental results show that Touzi decomposition can be effectively used for damage assessment mapping in built-up areas.