Abstract
Lakes are an essential component of biogeochemical processes, and variations in lake level are regarded as indicators of climate change. For more than a decade, satellite altimetry has successfully monitored variation in water levels over inland seas, lakes, rivers, and wetlands. Through altimetry, the surface water levels are measured at varying temporal scales depending on the orbit cycle of the satellite. The futuristic mission of Surface Water and Ocean Topography (SWOT) scheduled to be launched in year 2022 shall offer the spatial coverage and resolution suitable for water level estimation and volume calculation in small water bodies like lakes worldwide. With a radar interferometer in Ka-band, SWOT proposes to provide two-dimensional maps of water heights 21 days repeat orbit configuration. Cycle average SWOT datasets for land will be developed with higher temporal resolution, with temporal resolution varying geographically. This work assesses the potential of SWOT for monitoring water volumes over a case study lake by analyzing SWOT like synthetic data produced using the SWOT simulator developed by the Centre National d'Etudes Spatiales (CNES). With SWOT relying on a novel technology, the initial 90 days of this mission after launch shall focus on an extensive calibration and validation. Firsthand results of SWOT-simulated water levels and volumes are presented over a case study region in the tropical band, namely, Pookode Lake, in the ecologically fragile district of Wayanad, Kerala, India. It is the second-largest freshwater lake in Kerala that is being affected by anthropogenic activities, causing huge depletion in lake water storage in the last four decades. Our analysis indicated that the lake region is subjected to a rise in temperature of 0.018°C per year. We further assess the potential of remote sensing and SWOT data to monitor water storage of Pookode Lake, which is undergoing a rapid change. Results show that the proxy water surface elevations have immense potential in scientific studies pertaining to lake monitoring across the world. Overall, the study shows the potential of SWOT for monitoring the variability of water levels and volumes in this region.
Highlights
Surface water bodies are important sources of water for civilization, and they have a direct impact on ecosystems (Dudgeon et al, 2006; Palmer et al, 2015)
To generate synthetic Surface Water and Ocean Topography (SWOT) observations, the SWOT simulator uses a lake water extent shapefile with true Water Surface Elevation (WSE) as one of the attributes (CNES, 2020)
This study presents firsthand the results of the SWOT hydrology simulator to small lakes in India
Summary
Surface water bodies are important sources of water for civilization, and they have a direct impact on ecosystems (Dudgeon et al, 2006; Palmer et al, 2015). The aim of the SWOT satellite is to provide hydrologists with unprecedented observations of terrestrial water bodies in order to track changes in water volume These data are crucial for determining surface water availability and preparing for major water-related disasters like floods and droughts. To generate synthetic SWOT observations, the SWOT simulator uses a lake water extent shapefile with true WSE (details provided in Extraction of Water Level Using Interferometric SAR section) as one of the attributes (CNES, 2020). Surface area extent was computed from masked water bodies of sentinel photos Using this information, the change in volume ( v) for Pookode Lake after flood events was computed using Equation 3. Where h1 is the high water level in the lake (during the study period, i.e., 2020), h2 is the low water level (2015), A1 is lake surface area during 2020, and A2 is lake surface area during 2015
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