Large-Scale Retrieval of Coloured Dissolved Organic Matter in Northern Lakes Using Sentinel-2 Data

• Published in: Remote Sensing
• Main Authors: Enass Said. Al-Kharusi, David E. Tenenbaum, Abdulhakim M. Abdi, Tiit Kutser, Jan Karlsson, Ann-Kristin Bergström, Martin Berggren
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2020
• Subjects: sentinel-2a; northern lakes; remote sensing; atmospheric correction; coloured dissolved organic matter (cdom); water quality; Science; Q; Northern Sweden
• Online Access: https://doi.org/10.3390/rs12010157; https://doaj.org/article/58ece02abb414286b2a1838b1a2957eb

Owing to the significant societal value of inland water resources, there is a need for cost-effective monitoring of water quality on large scales. We tested the suitability of the recently launched Sentinel-2A to monitor a key water quality parameter, coloured dissolved organic matter (CDOM), in various types of lakes in northern Sweden. Values of a (420) CDOM (CDOM absorption at 420 nm wavelength) were obtained by analyzing water samples from 46 lakes in five districts across Sweden within an area of approximately 800 km 2 . We evaluated the relationships between a (420) CDOM and band ratios derived from Sentinel-2A Level-1C and Level-2A products. The band ratios B2/B3 (460 nm/560 nm) and B3/B5 (560 nm/705 nm) showed poor relationships with a (420) CDOM in Level-1C and 2A data both before and after the removal of outliers. However, there was a slightly stronger power relationship between the atmospherically-corrected B3/B4 ratio and a (420) CDOM (R 2 = 0.28, n = 46), and this relationship was further improved (R 2 = 0.65, n = 41) by removing observations affected by light haze and cirrus clouds. This study covered a wide range of lakes in different landscape settings and demonstrates the broad applicability of a (420) CDOM retrieval algorithms based on the B3/B4 ratio derived from Sentinel-2A.