Exploring Polarimetric Phase of Microwave Backscatter from Typha Wetlands

Despite their natural and societal importance, wetlands are becoming increasingly threatened. The goal of this study is to investigate the potential of polarimetric synthetic aperture radar (SAR) for monitoring one important vegetation constituent of wetlands: Typha. An idealized cylindrical scattering model is developed to portray double bounce microwave scattering from Typha stalks. Then a thin cylinder Brewster angle is introduced; relating the co-pol phase difference (CPD) of Typha to its relative permittivity. Full polarization Radarsat-2 data were acquired for a variety of dates and incidence angle ranges in order to validate the scattering model. The dependence of CPD on incidence angle is found to be consistent with the model. The evolution of CPD with seasonal senescence was also investigated. Despite some agreement with expected trends in vegetation moisture, there are anomalies that remain unexplained; possibly due to ecosystem change. This suggests the need for radar scatterometer experiments in a controlled environment to better explore the dependence of CPD on incidence angle and seasonal change. Last, cross-pol phase difference (XPD) histograms support other research in demonstrating the existence of coherent depolarization in Typha scattering. Additional modeling, entailing the detailed structure of the vegetation, will be necessary to understand this behavior.