Assessment of Chlorophyll-a Remote Sensing Algorithms in a Productive Tropical Estuarine-Lagoon System

Abstract

Remote estimation of chlorophyll-a in turbid and productive estuaries is difficult due to the optical complexity of Case 2 waters. Although recent advances have been obtained with the use of empirical approaches for estimating chlorophyll-a in these environments, the understanding of the relationship between spectral reflectance and chlorophyll-a is based mainly on temperate and subtropical estuarine systems. The potential to apply standard NIR-Red models to productive tropical estuaries remains underexplored. Therefore, the purpose of this study is to evaluate the performance of several approaches based on multispectral data to estimate chlorophyll-a in a productive tropical estuarine-lagoon system, using in situ measurements of remote sensing reflectance, R rs . The possibility of applying algorithms using simulated satellite bands of modern and recent launched sensors was also evaluated. More accurate retrievals of chlorophyll-a (r 2 > 0.80) based on field datasets were found using NIR-Red three-band models. In addition, enhanced chlorophyll-a retrievals were found using the two-band algorithm based on bands of recently launched satellites such as Sentinel-2/MSI and Sentinel-3/OLCI, indicating a promising application of these sensors to remotely estimate chlorophyll-a for coming decades in turbid inland waters. Our findings suggest that empirical models based on optical properties involving water constituents have strong potential to estimate chlorophyll-a using multispectral data from satellite, airborne or handheld sensors in productive tropical estuaries.

Remote Sensing of Water Quality Parameters over Lake Balaton by Using Sentinel-3 OLCI

“…Bands positioned in the red part of the electromagnetic spectrum, corresponding to the longer wavelengths, might be important due to the second absorption peak of the Chl-a molecule [39]. Recent studies have presented the benefit of using S3 OLCI red bands to monitor Chl-a in optically complex environments [40,41]. Chl-a estimation can be improved by using models with these red bands.…”

First Results of Phytoplankton Spatial Dynamics in Two NW-Mediterranean Bays from Chlorophyll-a Estimates Using Sentinel 2: Potential Implications for Aquaculture

“…IV. NR: The ratio between Red and NIR assumes that the absorption by non-algal particles, yellow substances and the backscattering are insignificant when compared to chl-a absorption at red wavelengths (665 nm) [35]. Between 700 and 720 nm, the absorption due to water constituents is minimal.…”

Optical Water Type Guided Approach to Estimate Optical Water Quality Parameters

“…Compared to other optical water quality parameter model selections, Chl-a varies the most between OWTs and the spectral range. The widely used [10,63,68,[87][88][89][90][91][92] ratio 700/670 nm with a high correlation for high-biomass waters, was the best model only for Turbid OWT with a Ramses spectral range. However, the two variables ratio approach was the best for all the spectral ranges in Brown OWT, OLCI and MSI Moderate OWT, Ramses Turbid OWT, and MSI Very Turbid OWT.…”

“…In our best-performing models, all variables were selected from the red and NIR spectral range, with different combinations. Moreover, broadly used [10,30,61,87,94,95] algorithms that include chlorophyll fluorescence information using values of reflectance spectra around 681 nm were not the best for any cases. The Brown OWT retrieving models coefficients of determination were about 40%, thus needing future investigation and improvement.…”