Popis: |
We reanalyze PacRim 2000 L-band AIRSAR polarimetry collected over the western foothills of central Taiwan a year after the September 20, 1999 ChiChi earthquake, which produced more than 10,000 landslides. The objective is to explore the utility of SAR data, particularly polarimetry, for identifying and mapping natural hazards like landslides that essentially resurface landscapes. An overall goal of this research is to exploit the operational advantages of radars over optical instruments for rapid assessment and response to natural hazards and disasters. Three flightlines of XTI1 AIRSAR were acquired over the two largest landslides, Tsaoling and Mt. Juo-feng-err, as well as hundreds of smaller slides generated by the ChiChi main and aftershocks. We first looked at the relative utility of single channel (co-polarized) SAR, dual polarimetry (co- and cross-polarized channels), and full polarimetry for landslide identification. We found that landslides are very difficult to recognize in fixed polarization SAR data. On the other hand, recognizing hillsides cleared of vegetation by landslides is relatively easy with dual and fully polarimetric data by using cross-polarized and co-polarized cross-sections to provide radar vegetation indices. Radar target decomposition methods applied to the L-band polarimetry allowed us to explore the changes in scattering mechanisms induced by the action of landsliding on forested hillslopes, and to use derived polarimetric parameters to identify landslides. Application of speckle reduction filters does not degrade the resolution with which small landslides can be mapped. Finally, we explored unsupervised classification methods for efficient mapping of landslides under a rapid response mode of operation. |