Wetland InSAR over the Everglades from space observed polarimetric data
Sang-Hoon Hong(1), Shimon Wdowinski(1) and Sang-Wan Kim(2)
(1) University of Miami, 4600 Rickenbacker Causeway, 33149, Miami, United States
(2) Sejong University, 98 Gunja-Dong Gwangjin-Gu, 143-147, Seoul, Korea
Interferometric and coherence analyses of the TerraSAR-X dual polarization mode observations (HH-HV, VV-VH) for Wetland InSAR applications over the south Florida reveal that interferometric phase maintains good coherences over both urban and wetland areas (all coherences > 0.40). The coherence of co-polarization is slightly better than that of cross-polarization, because the horizontal co-polarization of the radar signal is the dominant scattering behavior in wetland areas. The HH polarization yields the highest coherence (0.44) compared with other polarization interferograms (VV: 0.43, HV and VH: 0.42). A comparison between the co- and cross-polarization interferograms reveals that the fringe patterns in most regions are very similar despite the different polarization type. Interferometric coherence and fringes in wetlands occur due to double bounce scattering from the water surface and the emergent vegetation and reflect surface water level changes between the interferogram acquisition dates. Because of the very similar fringe pattern of both co- and cross polarization-interferograms, we suggest that cross-polarization in wetlands is also dominated by the double bounce scattering mechanism. This result indicates the volume scattered phases from vegetated areas are negligible with respect to double bounce scattering and that the cross-polarization phase information can be utilized for the interferometric processing over the wetland areas despite of short wavelength radar signal.
We also conducted a feasibility analysis of Radarsar-2 quad-polarimetric data acquired over the Everglades wetlands in south Florida. So far, we obtained only a single acquisition, which is not sufficient for PolInSAR, but still allows us to conduct PolSAR analysis. We used the Pauli and H-alpha decomposition approaches to investigate the scattering mechanism in the study area. Initial results indicate that in saltwater mangrove areas, which are located near by the open sea, volume scattering behavior is dominant. The main scattering mechanism over fresh water marsh covered by herbaceous vegetation is the even bounce scattering. These initial results are very promising and suggest that polarimetric data will be helpful to understand the scattering behavior of wetland areas. We will perform a full polarimetric interferometry analysis of the Radarsat-2 quad-polarimetric data after obtaining the next repeat pass acquisitions.