Validation and Comparison of Water Quality Products in Baltic Lakes Using Sentinel-2 MSI and Sentinel-3 OLCI Data

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.

Using Optical Water Types to Monitor Changes in Optically Complex Inland and Coastal Waters

“…Using the OWT classification performed in this study, it is possible to follow the movements of river water masses. Additionally, the OWT classification for larger lakes showed a reasonable correspondence with the results of previous studies [42][43][44][45]. Some small lakes and pixels affected by the adjacency effect were often classified as Clear.…”

Physics-based Bathymetry and Water Quality Retrieval Using PlanetScope Imagery: Impacts of 2020 COVID-19 Lockdown and 2019 Extreme Flood in the Venice Lagoon

“…Furthermore, information on bathymetry is critical for navigation purposes and the spatial variations of the water depth can be considered as an indicator of bed topography [1]. TSM refers to organic and mineral solids suspended in the water column, which is closely linked with water transparency/turbidity and Secchi disk depth [22]. The monitoring of TSM can contribute to the assessment of water quality and studies on sediment transportation [22,23].…”

“…TSM refers to organic and mineral solids suspended in the water column, which is closely linked with water transparency/turbidity and Secchi disk depth [22]. The monitoring of TSM can contribute to the assessment of water quality and studies on sediment transportation [22,23]. We examine the feasibility of a physics-based inversion of the PlanetScope radiometric data for retrieving bathymetry and TSM in a challenging shallow water environment.…”

Temporal and Spatial Variations of Secchi Depth and Diffuse Attenuation Coefficient from Sentinel-2 MSI over a Large Reservoir

“…The Sentinel-2 mission from the European Space Agency (ESA) is a land monitoring constellation of two satellites (S2A launched in June 2015 and S2B launched in March 2017) that provide high-resolution optical imagery (spatial resolution between 10 m and 60 m, depending on the spectral band) and presents a systematic global coverage of two to three days at mid-latitudes, which brought a great opportunity to study inland reservoirs. Several studies have been done in recent years in the analysis of water quality of inland waters using Sentinel-2 data, to measure water quality parameters of bodies of water [26][27][28][29][30][31].…”