Practical SAR orthorectification

SAR orthorectification procedures have been implemented at major processing facilities for several years, but only recently has workstation computer speed increased to a level where it is now practical for the SAR researcher to have their own orthorectification capability in-house. The present article presents the authors´ efforts to implement such a program and the practical lessons learned in doing so. Orthorectification encompasses all the corrections needed to precisely align a SAR image with a map, accounting for actual topography. However, there are several other operations that are required in order to produce radiometrically corrected data during the orthorectification process: calculating layover and shadow masks, local incidence angle, and calibration to σ⁰. Without calibration the image is far less useful in further processing, such as in land-cover classification and biophysical parameter estimation. Specifics of the authors´ effort to apply this to ERS PRI data, and to JERS level 2.1 data are presented, including an assessment of how well it performed