Abstract
The importance of lakes and reservoirs leads to the high need for monitoring lake water quality both at local and global scales. The aim of the study was to test suitability of Sentinel-2 Multispectral Imager’s (MSI) data for mapping different lake water quality parameters. In situ data of chlorophyll a (Chl a), water color, colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) from nine small and two large lakes were compared with band ratio algorithms derived from Sentinel-2 Level-1C and atmospherically corrected (Sen2cor) Level-2A images. The height of the 705 nm peak was used for estimating Chl a. The suitability of the commonly used green to red band ratio was tested for estimating the CDOM, DOC and water color. Concurrent reflectance measurements were not available. Therefore, we were not able to validate the performance of Sen2cor atmospheric correction available in the Sentinel-2 Toolbox. The shape and magnitude of water reflectance were consistent with our field measurements from previous years. However, the atmospheric correction reduced the correlation between the band ratio algorithms and water quality parameters indicating the need in better atmospheric correction. We were able to show that there is good correlation between band ratio algorithms calculated from Sentinel-2 MSI data and lake water parameters like Chl a (R2 = 0.83), CDOM (R2 = 0.72) and DOC (R2 = 0.92) concentrations as well as water color (R2 = 0.52). The in situ dataset was limited in number, but covered a reasonably wide range of optical water properties. These preliminary results allow us to assume that Sentinel-2 will be a valuable tool for lake monitoring and research, especially taking into account that the data will be available routinely for many years, the imagery will be frequent, and free of charge.
Highlights
Lakes and reservoirs act as regulators of carbon cycling and climate [1]
The highest values of chlorophyll a (Chl a), dissolved organic carbon (DOC), colored dissolved organic matter (CDOM) and water color were measured from Lake Lohja and Lake Võrtsjärv and the lowest from Lake Nohipalo Valgõjärv, Lake Rõuge Suurjärv and Lake Viitna Pikkjärv
There are several band ratio algorithms developed for estimating lake CDOM concentrations and closely related water color and DOC concentrations [18,35,36,37]
Summary
Lakes and reservoirs act as regulators of carbon cycling and climate [1]. They provide water for multiple human uses from drinking water to recreation and support high levels of biodiversity [2].There is a high need for monitoring lake water quality at local to global scales. Lakes and reservoirs act as regulators of carbon cycling and climate [1]. They provide water for multiple human uses from drinking water to recreation and support high levels of biodiversity [2]. There is a high need for monitoring lake water quality at local to global scales. Increasing amount of lakes has been equipped with automated monitoring systems [4,5] that provided data with sufficient frequency. Satellite remote sensing is the only feasible way to monitor lakes when we have global questions (like carbon cycle) under investigation, or when water quality over large regions has to be monitored with reasonable frequency
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