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Interferometric synthetic aperture radar (InSAR) techniques can successfully detect phase variations related to the water level changes in wetlands and produce high spatial resolution maps of water level changes. We present a new InSAR technique, termed small temporal baseline subset (STBAS), for monitoring not relative but absolute water levels and their variations with time (time series) using successive radar observations over wetlands. Our approach follows the small baseline subset (SBAS) used for monitoring displacement time series of solid earth surfaces. The new STBAS algorithm utilizes highly coherent interferometric phases obtained only with relatively short time difference regardless of spatial baseline. We tested the STBAS technique with two year long Radarsat-1 data acquired over a small section of the Everglades wetlands in south Florida (USA). Our study uses ground-based stage (water level) data for calibration and validation, which indicate a good fit between the InSAR the stage data. The new STBAS technique can transform relative wetland InSAR observations to absolute frame and generates both detailed maps of water levels, as well as water level time series for almost each pixel (50 m resolution).