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Open AccessArticle

Optical Water Type Guided Approach to Estimate Optical Water Quality Parameters

1
Tartu Observatory, University of Tartu, 50090 Tartu, Estonia
2
Department of Marine Systems, School of Science, Tallinn University of Technology, 12616 Tallinn, Estonia
3
Estonian Marine Institute, University of Tartu, 12618 Tallinn, Estonia
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(6), 931; https://doi.org/10.3390/rs12060931
Received: 10 February 2020 / Revised: 9 March 2020 / Accepted: 11 March 2020 / Published: 13 March 2020
Currently, water monitoring programs are mainly based on in situ measurements; however, this approach is time-consuming, expensive, and may not reflect the status of the whole water body. The availability of Multispectral Imager (MSI) and Ocean and Land Colour Instrument (OLCI) free data with high spectral, spatial, and temporal resolution has increased the potential of adding remote sensing techniques into monitoring programs, leading to improvement of the quality of monitoring water. This study introduced an optical water type guided approach for boreal regions inland and coastal waters to estimate optical water quality parameters, such as the concentration of chlorophyll-a (Chl-a) and total suspended matter (TSM), the absorption coefficient of coloured dissolved organic matter at a wavelength of 442 nm (aCDOM(442)), and the Secchi disk depth, from hyperspectral, OLCI, and MSI reflectance data. This study was based on data from 51 Estonian and Finnish lakes and from the Baltic Sea coastal area, which altogether were used in 415 in situ measurement stations and covered a wide range of optical water quality parameters (Chl-a: 0.5–215.2 mg·m−3; TSM: 0.6–46.0 mg·L−1; aCDOM(442): 0.4–43.7 m−1; and Secchi disk depth: 0.2–12.2 m). For retrieving optical water quality parameters from reflectance spectra, we tested 132 empirical algorithms. The study results describe the best algorithm for each optical water type for each spectral range and for each optical water quality parameter. The correlation was high, from 0.87 up to 0.93, between the in situ measured optical water quality parameters and the parameters predicted by the optical water type guided approach. View Full-Text
Keywords: optical water type; chlorophyll-a; total suspended matter; CDOM; Secchi disk depth; Sentinel-3 OLCI; Sentinel-2 MSI; lakes; Baltic Sea optical water type; chlorophyll-a; total suspended matter; CDOM; Secchi disk depth; Sentinel-3 OLCI; Sentinel-2 MSI; lakes; Baltic Sea
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MDPI and ACS Style

Uudeberg, K.; Aavaste, A.; Kõks, K.-L.; Ansper, A.; Uusõue, M.; Kangro, K.; Ansko, I.; Ligi, M.; Toming, K.; Reinart, A. Optical Water Type Guided Approach to Estimate Optical Water Quality Parameters. Remote Sens. 2020, 12, 931.

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