C-band Radar Observes Water-level Change in Coastal Louisiana Swamp Forests

It is commonly recognized that C-band (wavelength of 5.7 cm) radar pulses backscatter from the upper canopy of swamp forests. Consequently, interferometric analysis of C-band imagery has not been exploited to study water-level changes in swamp forests. Using C-band ERS-1 and ERS-2 radar images, we show that interferometric synthetic aperture radar (InSAR) images maintain adequate coherence over swamp forests composed of moderately dense trees with a medium-low canopy closure in southeastern Louisiana over a time window of a few months. The InSAR images acquired during leaf-off seasons (October - April) can maintain coherence up to 5 years. This unexpected phenomenon is believed to be due to double-bounce returns of C-band radar signal reflecting off tree trunks and the water surface. The persistent coherence of C-band radar signal over swamp forests allows us to measure changes in water-level beneath tree cover with an unprecedented degree of vertical accuracy. Future InSAR images with shorter repeat times will be capable of characterizing the temporal evolution of water-level changes to improve hydrological modeling predictions and enhance assessments of future flood hazards over wetlands.