Amazon floodplain water level changes measured with interferometric SIR-C radar

We find that interferometric processing of repeat-pass L-HH-band shuttle im aging radar (SIR-C) data reveals centimeter-scale changes in the elevations of water surfaces within flooded vegetation, Because radar pulses reflect specularly from the water surface, interferometric observations of open wat er are incoherent. However, within flooded forests and inundated shrubs, th e L-band radar pulse penetrates the vegetation canopy and follows a double- bounce travel path that includes the water and vegetation-trunk surfaces. I n these environments, the returned radar energy and associated phase cohere nce are both stronger than the surrounding nonflooded terrain, permitting d etermination of the interferometric phase. Phase errors related to atmosphe ric water vapor are usually longer in wavelength and spatially distinct fro m phase signatures related to stage changes in tributaries and floodplain l akes. The interferometrically measured stage decreases match gauge data, pr oviding further verification. Water level changes across 150 m to 2.75 km-w ide water bodies containing inundated vegetation can be reliably measured. Our results suggest that if future interferometric L-HH-band SAR missions a re implemented with short temporal baselines, it is possible to measure the hydrologic response of wetlands and inundated floodplains to changes in ma instem water level.