Potential of ENVISAT Radar Altimetry for Water Level Monitoring in the Pantanal Wetland

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.

Sentinel-3 radar altimetry for river monitoring – a catchment-scale evaluation of satellite water surface elevation from Sentinel-3A and Sentinel-3B

“…The instruments operate 100 % in SAR mode between 60 • N and 60 • S, making Sentinel-3 the first satellite altimetry mission to provide near global coverage in SAR mode. SAR altimeters have improved data quality and accuracy in coastal areas and over inland water thanks to the smaller along-track footprint, which is less affected by land contamination (Dinardo et al, 2018;Jiang et al, 2017b;Nielsen et al, 2017;Wingham et al, 2006). Thus smaller water bodies, including narrower rivers, can be sensed by the altimeter (Villadsen et al, 2016).…”

Remote Sensing of Boreal Wetlands 1: Data Use for Policy and Management

“…SAR is used extensively for mapping water extents and relative water level change to establish the hydroperiod (over multiple acquisition dates) [22,23,184,189,196,199,203,278,279]. When combined with a high-resolution DEM from lidar or another sensor (e.g., SRTM), the combination of ground surface elevation and open water extent can be used to estimate water level [23,118,186,189,265]. SAR backscatter (defined as the reflected microwave radiation from an intentionally illuminated object) results in specular reflectance over calm water bodies as the backscattered signal is directed away from the sensor.…”

Spatial and Temporal Variations of Terrestrial Water Storage in Upper Indus Basin Using GRACE and Altimetry Data

“…Therefore, the returned waveforms must be analyzed carefully to avoid errors in the measurement range. To eliminate noisy waveforms from each altimetry data set, a parameter Sigma0 or the radar backscatter coefficient, was used as an efficient criterion for classifying the reflected surface property [61], [62]. The waveform with a Sigma0 of less than zero was considered a noisy wave and was discarded.…”