Abstract
Inland waters, including lakes, are one of the key points of the carbon cycle. Using remote sensing data in lake monitoring has advantages in both temporal and spatial coverage over traditional in-situ methods that are time consuming and expensive. In this study, we compared two sensors on different Copernicus satellites: Multispectral Instrument (MSI) on Sentinel-2 and Ocean and Land Color Instrument (OLCI) on Sentinel-3 to validate several processors and methods to derive water quality products with best performing atmospheric correction processor applied. For validation we used in-situ data from 49 sampling points across four different lakes, collected during 2018. Level-2 optical water quality products, such as chlorophyll-a and the total suspended matter concentrations, water transparency, and the absorption coefficient of the colored dissolved organic matter were compared against in-situ data. Along with the water quality products, the optical water types were obtained, because in lakes one-method-to-all approach is not working well due to the optical complexity of the inland waters. The dynamics of the optical water types of the two sensors were generally in agreement. In most cases, the band ratio algorithms for both sensors with optical water type guidance gave the best results. The best algorithms to obtain the Level-2 water quality products were different for MSI and OLCI. MSI always outperformed OLCI, with R2 0.84–0.97 for different water quality products. Deriving the water quality parameters with optical water type classification should be the first step in estimating the ecological status of the lakes with remote sensing.
Highlights
Lake water quality can be determined by its optical properties, as the concentrations of chlorophyll-a (Chl-a) and the total suspended matter (TSM), the absorption coefficient of colored dissolved organic matter (CDOM), and transparency of the water measured by Secchi disk
We found 41 Multispectral Instrument (MSI) match-ups for 35 different sampling points, from witch 6 sampling points had 2 match-up images; and 79 Ocean and Land Color Instrument (OLCI) match-ups for 42 different sampling points, from witch 28 sampling points had more than one match-up images
The water transparency decreased towards the summer and again increased in autumn, in all of the studied lakes
Summary
The importance of inland water bodies has never been greater, because inland water, including lakes, are one of the key points of the carbon cycle and, local and regional climate [1,2].Lakes are economically important as a source of drinking water, and provide fishing and recreation opportunities; the monitoring of the water quality has become a global concern.In Europe, for example, the Water Framework Directive [3] is aiming to achieve good water quality status in all lakes larger than 0.5 km2 .Lake water quality can be determined by its optical properties, as the concentrations of chlorophyll-a (Chl-a) and the total suspended matter (TSM), the absorption coefficient of colored dissolved organic matter (CDOM), and transparency of the water measured by Secchi disk (SecchiSensors 2020, 20, 742; doi:10.3390/s20030742 www.mdpi.com/journal/sensorsSensors 2020, 20, 742 depth, SD). Lakes are economically important as a source of drinking water, and provide fishing and recreation opportunities; the monitoring of the water quality has become a global concern. In Europe, for example, the Water Framework Directive [3] is aiming to achieve good water quality status in all lakes larger than 0.5 km. Lake water quality can be determined by its optical properties, as the concentrations of chlorophyll-a (Chl-a) and the total suspended matter (TSM), the absorption coefficient of colored dissolved organic matter (CDOM), and transparency of the water measured by Secchi disk D.R., State-of-the-Art. In Bio-optical Modeling and Remote Sensing of Inland Waters; Mishra, D.R.; Ogashawara, I.; I., Elsevier. Cyanobacterial toxins, the perception of water quality, and and the prioritization of eutrophication control
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