Impact of DEM source on Radarsat-2 polarimetric information during ortho-rectification

Abstract

Ortho-rectification using digital terrain models is a key issue for full polarimetric complex synthetic aperture radar (SAR) data because resampling the complex data can corrupt the polarimetric phase, mainly in terrain with relief. Two methods for ortho-rectification of the complex SAR data can be applied: the polarimetric processing is performed before (image-space method) or after (ground-space method) the geometric processing. This research evaluated the impact of the digital elevation models (DEMs), which are generally available to users (topographic DEM and ASTER GDEM V2). The two methods were applied to three Radarsat-2 fine-quad data acquired with different look angles over a hilly relief study site. Quantitative evaluations between the two approaches as a function of different geometric and radiometric parameters were, thus, performed to evaluate the impact during the ortho-rectification. The results demonstrated that the look angles and the terrain slopes can potentially corrupt the single-look polarimetric complex SAR data during its ortho-rectification with the ground-space method, mainly at the layover limit. However, advice is provided to reduce these impacts to an acceptable level.

Keywords:

• SAR
• polarimetry
• ortho-rectification
• DEM
• Radarsat-2

Acknowledgements

The Authors thank M. Paul Briand and the Canadian Space Agency under its GRIP and SOAR programmes for the financial contribution and the Radarsat-2 data. They also thank MM. Eric Pottier and Cédric Lardeux of I.E.T.R, Université de Rennes 1 for scientific advice in polarimetry and operational support in PolSARpro. ESS Contribution number/Numéro de contribution du SST: 20120357.