Monitoring turbidity in a highly variable estuary using Sentinel 2-A/B for ecosystem management applications

Frontiers in Marine Science

Marine Science

Stef van Bergeijk¹  César Vilas²  Gabriel Navarro³  Isabel Caballero³  Irene Laiz⁴  Masuma Chowdhury⁵ 

[1] Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA)-Centro El Toruño El Puerto de Santa Maria, Cádiz, Spain;Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA)-Centro El Toruño El Puerto de Santa Maria, Cádiz, Spain;Associate Research Unit “Blue Growth” Spanish National Research Council (CSIC) - Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA), Cádiz, Spain;Associate Research Unit “Blue Growth” Spanish National Research Council (CSIC) - Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA), Cádiz, Spain;Department of Ecology and Coastal Management, Institute of Marine Sciences of Andalusia (ICMAN) - Spanish National Research Council (CSIC), Puerto Real, Cádiz, Spain;Departamento de Física Aplicada, Instituto Universitario de Investigación Marina (INMAR), Universidad de Cádiz, Puerto Real, Cádiz, Spain;Departamento de Física Aplicada, Instituto Universitario de Investigación Marina (INMAR), Universidad de Cádiz, Puerto Real, Cádiz, Spain;Quasar Science Resources, S. L., Madrid, Spain;

关键词: Sentinel-2;    atmospheric correction;    multi-conditional algorithm;    turbidity;    Guadalquivir estuary;    ecosystem management;   

DOI  :  10.3389/fmars.2023.1186441

 received in 2023-03-14, accepted in 2023-06-23,  发布年份 2023

来源: Frontiers

【 摘 要 】

The Guadalquivir estuary (southern Spain) occasionally experiences medium to high turbidity, reaching above 700 Formazin Nephelometric Unit (FNU) during extreme events, thus negatively influencing its nursery function and the estuarine community structure. Although several turbidity algorithms are available to monitor water quality, they are mainly developed for mapping turbidity ranges of 0-100 FNU. Thus, their use in a highly turbid region may not give accurate results, which is crucial for estuarine ecosystem management. To fill this gap, we developed a multi-conditional turbidity algorithm that can retrieve turbidity from 0 to 600 FNU using the Sentinel-2 red and red-edge bands. Four major steps are implemented: atmospheric and sun glint correction of the Level-1C Sentinel-2 data, spectral analysis for different water turbidity levels, regression modelling between in situ turbidity and remote sensing reflectance (Rrs) for algorithm development, and validation of the best-suited model. When turbidity was < 85 FNU, the Rrs increased firstly in the red wavelength (665 nm), but it saturated beyond a certain turbidity threshold (> 250 FNU). At this time, Rrs started to increase in the red-edge wavelength (704 nm). Considering this spectral behavior, our algorithm is designed to automatically select the most sensitive turbidity vs. Rrs, thus avoiding the saturation effects of the red bands at high turbidity levels. The model showed good agreement between the satellite derived turbidity and the in situ measurements with a correlation coefficient of 0.97, RMSE of 15.93 FNU, and a bias of 13.34 FNU. Turbidity maps derived using this algorithm can be used for routine turbidity monitoring and assessment of potential anthropogenic actions (e.g., dredging activities), thus helping the decision-makers and relevant stakeholders to protect coastal resources and human health.

【 授权许可】

Unknown   
Copyright © 2023 Chowdhury, Vilas, van Bergeijk, Navarro, Laiz and Caballero