Validation of standard ocean-color chlorophyll-a products in turbid coastal waters: A case study on statistical evaluation and quality control tests in the Persian Gulf
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引用次数: 1
Abstract
Selecting the appropriate in-situ and satellite matchups is a critical task for evaluating and application of ocean color products in optically complex coastal waters. This article investigates the performance of five single-sensor and two merged multi-sensors Chl-a products in the Persian Gulf. In this study, bio-optical and Chl-a measurements collected from 531 stations in the northern Persian Gulf from 2008 to 2019 were used. In-situ samples were initially controlled to filter out inappropriate datasets. Results indicated that surface measurements may not be representative of satellite-derived Chl-a, and satellite estimations were mostly consistent with Chl-a concentrations in the first optical depth (Chlopt). Statistical analysis showed that all satellite-derived Chl-a products overestimated the Chlopt by 48%–170%, in which Chl-a from Neural-Network and OC5 algorithms yielded the best agreement. Afterwards, the QC tests were designed based on the remote sensing reflectance (Rrs) at 555 nm as a proxy of SPM, Rrs(412)/Rrs(443) as a proxy of CDOM, and Rrs(560)/Rrs(490) as a proxy of Chl-a, to select the matchups with the least interference of Colored Dissolved Organic Matter (CDOM) and Suspended Particulate Matter (SPM) on Chl-a. The correlation between Chlopt and satellite-derived Chl-a improved significantly after applying the QC tests (R2 = 0.80–0.89). The valid pixels were determined using matching the results of QC tests and standard level-2 quality flags. Finally, statistical calibration was used to create the final quality controlled calibrated Chl-a maps, using regression coefficients obtained from training/validation exercises and bootstrapping-like techniques applied to the quality-controlled datasets. The findings showed that in turbid coastal waters, standard ocean color Chl-a products cannot be validated only by performing statistical methods, and quality control experiments are necessary for their applications.
期刊介绍:
The Journal of Marine Systems provides a medium for interdisciplinary exchange between physical, chemical and biological oceanographers and marine geologists. The journal welcomes original research papers and review articles. Preference will be given to interdisciplinary approaches to marine systems.