Detection of Envisat RA2/ICE-1 retracked radar altimetry bias over the Amazon basin rivers using GPS |
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Authors: | Stéphane Calmant Joecila Santos da Silva Daniel Medeiros Moreira Frédérique Seyler CK Shum Jean François Crétaux Germinal Gabalda |
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Institution: | 1. IRD/LEGOS, 14 Av. Edouard Belin, 31400 Toulouse, France;2. UEA/CESTU, Av. Djalma Batista 3578, 69058-807 Manaus, Brazil;3. UFRJ/CPRM, Av. Pasteur 404, 22290-040 Rio de Janeiro, Brazil;4. IRD/ESPACE-DEV, 500 Rue Jean François Breton, 34093 Montpellier, France;5. Division of Geodetic Sciences, OSU/SES, 125 South Oval Mall, Columbus, 43210 OH, United States;6. CNES/LEGOS, 14 Av. Edouard Belin, 31400 Toulouse, France;g IRD/GET, 14 Av. Edouard Belin, 31400 Toulouse, France |
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Abstract: | Altimetry is now routinely used to monitor stage variations over rivers, including in the Amazon basin. It is desirable for hydrologic studies to be able to combine altimetry from different satellite missions with other hydrogeodesy datasets such as leveled gauges and watershed topography. One requirement is to accurately determine altimetry bias, which could be different for river studies from the altimetry calibrated for deep ocean or lake applications. In this study, we estimate the bias in the Envisat ranges derived from the ICE-1 waveform retracking, which are nowadays widely used in hydrologic applications. As a reference, we use an extensive dataset of altitudes of gauge zeros measured by GPS collocated at the gauges. The thirty-nine gauges are spread along the major tributaries of the Amazon basin. The methodology consists in jointly modeling the vertical bias and spatial and temporal slope variations between altimetry series located upstream and downstream of each gauge. The resulting bias of the Envisat ICE-1 retracked altimetry over rivers is 1.044 ± 0.212 m, revealing a significant departure from other Envisat calibrations or from the Jason-2 ICE-1 calibration. |
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Keywords: | Altimetry bias Envisat Amazon basin Hydrology |
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