Abstract
Wetlands are important ecosystems playing an essential role for continental water regulation and the hydrologic cycle. Moreover, they are sensitive to climate changes as well as anthropogenic influences, such as land-use or dams. However, the monitoring of these regions is challenging as they are normally located in remote areas without in situ measurement stations. Radar altimetry provides important measurements for monitoring and analyzing water level variations in wetlands and flooded areas. Using the example of the Pantanal region in South America, this study demonstrates the capability and limitations of ENVISAT radar altimeter for monitoring water levels in inundation areas. By applying an innovative processing method consisting of a rigorous data screening by means of radar echo classification as well as an optimized waveform retracking, water level time series with respect to a global reference and with a temporal resolution of about one month are derived. A comparison between altimetry-derived height variations and six in situ time series reveals accuracies of 30 to 50 cm RMS. The derived water level time series document seasonal height variations of up to 1.5 m amplitude with maximum water levels between January and June. Large scale geographical pattern of water heights are visible within the wetland. However, some regions of the Pantanal show water level variations less than a few decimeter, which is below the accuracies of the method. These areas cannot be reliably monitored by ENVISAT.
Highlights
Radar altimetry was designed to provide highly accurate measurements of sea surface heights over open ocean areas on a global scale
Focusing on the example of Pantanal, the present study investigates the capability of radar altimetry to monitor water level variations of large inundation areas
The root mean square (RMS) differences are between 30 and 50 cm. These values are in the same order of magnitude with the results from the crossover analysis (Section 4.4.1) and the formal errors of the altimetry time series
Summary
Radar altimetry was designed to provide highly accurate measurements of sea surface heights over open ocean areas on a global scale. Using radar altimetry for wetland water monitoring is both: (1) a great possibility for deriving hydrologic information in mostly remote areas where in large parts infrastructure is missing and no in situ observations are available and (2) a challenge for data processing as only small areas with open water exist that change rapidly with time. Focusing on the example of Pantanal, the present study investigates the capability of radar altimetry to monitor water level variations of large inundation areas. Several interesting studies exist on this inundation area, mainly dealing with the extent of water areas and consequences for the ecosystem, among them Hamilton et al [27], Hamilton et al [28], Evans et al [29], Evans and Costa [30], Girard et al [31], and Padovani [32] All these studies rely on sparse in situ gauging stations to derive water level time series.
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