Applications of Synthetic Aperture Radar (SAR)/ SAR Interferometry (InSAR) for Monitoring of Wetland Water Level and Land Subsidence

Development of coastal wetlands and arid areas had negative impacts on the natural hydrological processing on the surface and underground, and it resulted in disappearance of wetlands that buffer severe flooding and function as home for various wildlife in the wetlands, and groundwater depletion in the desert areas. Continuously monitoring the surface change caused by human activities requires radar remote sensing with the in-situ measurements. The intensity and phase components of Synthetic Aperture Radar (SAR) data provide valuable information on the characteristics of surface change and ground deformation. First of all, in this study, we demonstrated that the wetland water level changes in the Atchafalaya Basin of the Louisiana can be effectively observed by integrating Interferometric SAR (InSAR) results and radar altimetry data. When the hydrologic flow between wetlands is disrupted by levees or dams, InSAR processing cannot appropriately resolve the absolute water level changes from unwrapped phases. The fusion of the two radar technologies enables one to accurately estimate absolute water level change while avoiding inconsistent phase unwrapping. Secondly, the water level in the Everglades is measured by monitoring stations, and the measurement is often disturbed by abrupt water level rise. The L-band SAR backscatter coefficient in Everglades has the characteristics that SAR intensity is inversely proportional with water level in the freshwater marsh. The linear relationship enables one to estimate water level from SAR backscattering coefficients. The correlation between two parameters over the sawgrass was high, and it implied that water level estimation from the ALOS L-band SAR backscatter coefficients is possible. The final study demonstrated the use of small baseline subset (SBAS) InSAR processing technique to effectively measure the ground subsidence caused by groundwater depletion in Tucson, Arizona. The SBAS processing suppresses atmospheric artifacts affected by turbulent mixing that appears random in time and space and estimates topographic error terms from multiple InSAR pairs. The SBAS InSAR-derived vertical deformation gives information on the spatial extent and magnitude of subsidence. The groundwater level decrease of tens of meter caused the ground subsidence of tens of centimeters over a 17-years time period. InSAR results indicate that the subsidence has recently slowed down possibly due to the artificial recharge of water into surrounding aquifers near Tucson, Arizona.