Abstract
Remote sensing data are essential for monitoring the Earth’s surface waters, especially since the amount of publicly available in-situ data is declining. Satellite altimetry provides valuable information on the water levels and variations of lakes, reservoirs and rivers. In combination with satellite imagery, the derived time series allow the monitoring of lake storage changes and river discharge. However, satellite altimetry is limited in terms of its spatial resolution due to its measurement geometry, only providing information in the nadir direction beneath the satellite’s orbit. In a case study in the Mississippi River Basin (MRB), this study investigates the potential and limitations of past and current satellite missions for the monitoring of basin-wide storage changes. For that purpose, an automated target detection is developed and the extracted lake surfaces are merged with the satellites’ tracks. This reveals that the current altimeter configuration misses about 80% of all lakes larger than 0.1 km2 in the MRB and 20% of lakes larger than 10 km2, corresponding to 30% and 7% of the total water area, respectively. Past altimetry configurations perform even more poorly. From the larger water bodies represented by a global hydrology model, at least 91% of targets and 98% of storage changes are captured by the current altimeter configuration. This will improve significantly with the launch of the planned Surface Water and Ocean Topography (SWOT) mission.
Highlights
Freshwater resources are critical for human life
The focus of this study is to investigate the capability of different satellite altimetry configurations to measure basin-wide lake storage changes
While the number of detected water bodies was very close to the number given in Global Lakes and Wetlands Database (GLWD) (Level 1 and Level 2), which is 4647, the total area is underestimated by almost 4600 km2
Summary
Freshwater resources are critical for human life. About 2.5% of the Earth’s water is freshwater, of which most is embedded in ice and in the ground [1]. About 0.25% of the world’s freshwater is stored in lakes and reservoirs. Knowledge about its availability and changes is essential for water management as well as for monitoring climate change. Even though extensive and precise in-situ monitoring systems for some regions have been installed, the knowledge about global water storage is still limited. Global models such as the WaterGap Global Hydrology Model (WGHM) [2] can provide valuable but uncertain information. In order to provide reliable results, they need to be calibrated by observation data [3]
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