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Article

Inter-Comparison of Methods for Chlorophyll-a Retrieval: Sentinel-2 Time-Series Analysis in Italian Lakes

1
Digital Society Center, Fondazione Bruno Kessler, Via Sommarive 18, I-38123 Trento, Italy
2
Department of Information Engineering and Computer Science, University of Trento, Via Sommarive 5, I-38123 Trento, Italy
3
German Aerospace Center (DLR), Remote Sensing Technology Institute, Münchner Str. 20, Oberpfaffenhofen, D-82234 Weßling, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Deepak R. Mishra
Remote Sens. 2021, 13(12), 2381; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13122381
Received: 14 April 2021 / Revised: 11 June 2021 / Accepted: 15 June 2021 / Published: 18 June 2021
Different methods are available for retrieving chlorophyll-a (Chl-a) in inland waters from optical imagery, but there is still a need for an inter-comparison among the products. Such analysis can provide insights into the method selection, integration of products, and algorithm development. This work aims at inter-comparison and consistency analyses among the Chl-a products derived from publicly available methods consisting of Case-2 Regional/Coast Colour (C2RCC), Water Color Simulator (WASI), and OC3 (3-band Ocean Color algorithm). C2RCC and WASI are physics-based processors enabling the retrieval of not only Chl-a but also total suspended matter (TSM) and colored dissolved organic matter (CDOM), whereas OC3 is a broadly used semi-empirical approach for Chl-a estimation. To pursue the inter-comparison analysis, we demonstrate the application of Sentinel-2 imagery in the context of multitemporal retrieval of constituents in some Italian lakes. The analysis is performed for different bio-optical conditions including subalpine lakes in Northern Italy (Garda, Idro, and Ledro) and a turbid lake in Central Italy (Lake Trasimeno). The Chl-a retrievals are assessed versus in situ matchups that indicate the better performance of WASI. Moreover, relative consistency analyses are performed among the products (Chl-a, TSM, and CDOM) derived from different methods. In the subalpine lakes, the results indicate a high consistency between C2RCC and WASI when aCDOM(440) < 0.5 m−1, whereas the retrieval of constituents, particularly Chl-a, is problematic based on C2RCC for high-CDOM cases. In the turbid Lake Trasimeno, the extreme neural network of C2RCC provided more consistent products with WASI than the normal network. OC3 overestimates the Chl-a concentration. The flexibility of WASI in the parametrization of inversion allows for the adaptation of the method for different optical conditions. The implementation of WASI requires more experience, and processing is time demanding for large lakes. This study elaborates on the pros and cons of each method, providing guidelines and criteria on their use. View Full-Text
Keywords: method comparison; water quality; lake; chlorophyll-a; TSM; CDOM; C2RCC; WASI; OC3; product consistency; multitemporal analysis; Sentinel-2 method comparison; water quality; lake; chlorophyll-a; TSM; CDOM; C2RCC; WASI; OC3; product consistency; multitemporal analysis; Sentinel-2
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MDPI and ACS Style

Niroumand-Jadidi, M.; Bovolo, F.; Bruzzone, L.; Gege, P. Inter-Comparison of Methods for Chlorophyll-a Retrieval: Sentinel-2 Time-Series Analysis in Italian Lakes. Remote Sens. 2021, 13, 2381. https://0-doi-org.brum.beds.ac.uk/10.3390/rs13122381

AMA Style

Niroumand-Jadidi M, Bovolo F, Bruzzone L, Gege P. Inter-Comparison of Methods for Chlorophyll-a Retrieval: Sentinel-2 Time-Series Analysis in Italian Lakes. Remote Sensing. 2021; 13(12):2381. https://0-doi-org.brum.beds.ac.uk/10.3390/rs13122381

Chicago/Turabian Style

Niroumand-Jadidi, Milad, Francesca Bovolo, Lorenzo Bruzzone, and Peter Gege. 2021. "Inter-Comparison of Methods for Chlorophyll-a Retrieval: Sentinel-2 Time-Series Analysis in Italian Lakes" Remote Sensing 13, no. 12: 2381. https://0-doi-org.brum.beds.ac.uk/10.3390/rs13122381

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