Estimation of surface topography from single polarimetric SAR imagery using RADARSAT2

In this paper a practical method is demonstrated for estimating terrain slopes in azimuth and ground range directions for digital elevation model (DEM) generation without any prior knowledge on the terrain by using only one single pass of polarimetric synthetic aperture radar (PolSAR) instead of two-pass or interferometric SAR (INSAR). The basic approach is by combing the orientation angle estimation and a shape-from-shading technique (SFS) which is mostly used by the computer vision community. In particular, when limited PolSAR data are available, this technique provides an alternative way for DEM generation. The polarization orientation angle (POA) is related to both the range and azimulh angles of the tilted surface and radar viewing angle and it can be estimated from the PolSAR data by using the circular polarization method which shows the best performance in computation efficiency and accuracy with respect to the other methods. After terrain slopes in both the range and azimuth directions have been estimated initially by the combination of the POA estimation and the SFS algorithm, a least squares method similar to that used in interferometric phase unwrapping is used to generate the topography. The least squares approach to phase unwrapping obtains an unwrapped solution by minimizing the differences between the discrete partial derivatives of the (wrapped) phase data and the discrete partial derivatives of the unwrapped solution. We illustrate our results by using the polarimetric SAR images acquired in Algeria by the RadarSAT2 (FQ19) in C-band.