Evaluation of ocean chlorophyll-a remote sensing algorithms using in situ fluorescence data in Southern Brazilian Coastal Waters

Carlos Alberto Eiras Garcia,Gabriel Serrato De Mendonça Silva

doi:10.1590/2675-2824069.20-014gsdms

Carlos Alberto Eiras Garcia, Gabriel Serrato De Mendonça Silva

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https://doi.org/10.1590/2675-2824069.20-014gsdms

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Abstract

Abstract A performance evaluation of ocean color chlorophyll-a algorithms was conducted based on the in situ fluorescence chlorophyll concentration (Fchl) measured by a sensor on the buoy SiMCosta-SC01 in coastal waters of South Brazil. The operational algorithms are used in MODIS and VIIRS sensors to derive satellite chlorophyll concentration (Csat). Fchl values were successfully corrected for nonphotochemical quenching (NPQ) by an interpolation of sunrise and sunset daily measurements. A laboratory-derived calibration coefficient was applied to convert the unquenching Fchl values into chlorophyll concentration (Cflu). Overall, linear regression analysis between Cflu and Csat for both sensors showed good results, with the coefficient of determination (R2) varying between 0.88 and 0.96, slopes between 0.92 and 1.02 and intercepts between -0.17 and 0.13. The MODIS algorithm (R2 = 0.96, slope = 1.02, RMSE = 0.16 mg m-3, BIAS = 0.16 mg m-3, for N = 222 and time interval ±1 h) presented slightly better performance than VIIRS (R2 = 0.92, slope = 0.96, RMSE = 0.25 mg m-3, BIAS = -0.25 mg m-3, for N = 284 and time interval ±1 h). These results represent the most comprehensive satellite data analysis for this region, suggesting that the approach may be applicable to other SiMCosta buoys.

Highlights

Technological advances in space missions in recent decades have allowed the development of sensors such as the Coastal Zone Color Scanner (CZCS), Moderate Resolution Imaging Spectroradiometer (MODIS) (Salomonson et al, 1989), Ocean Color and Temperature Scanner (OCTS) (Iwasaki et al, 1992), Submitted: 09-October-2020 Approved: 15-February-2021 Editor: Rubens M
The studied region is regularly occupied by Subtropical Shelf Water (STSW) (Bordin et al, 2019) - a mixture of La Plata Plume Water (PPW) and Tropical Water (TW) (Moller et al, 2008) - with higher influence of Plate River Plume Water (PPW) (TW) in wintertime (Moller et al, 2008; Bordin et al 2019)
Our results have shown that the differences between Csat and Cflu do not depend on photosynthetically active radiation (PAR) measurements (Figure 11a) and time of year (Figure 11b), which reflects the good correction for nonphotochemical quenching in the measurements of in situ chlorophyll-a from fluorescence data

Summary

Introduction

Technological advances in space missions in recent decades have allowed the development of sensors such as the Coastal Zone Color Scanner (CZCS), Moderate Resolution Imaging Spectroradiometer (MODIS) (Salomonson et al, 1989), Ocean Color and Temperature Scanner (OCTS) (Iwasaki et al, 1992), Submitted: 09-October-2020 Approved: 15-February-2021 Editor: Rubens M. Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (Hooker et al, 1992), Medium Resolution Imaging Spectrometer (MERIS) (Rast and Bezy, 1999) and, more recently, Visible Infrared Imager / Radiometer Suite (VIIRS) (Welsch et al, 2001). Such development permitted researchers to conduct pioneering ocean color studies with high spatial and temporal resolutions. 2008; Henson et al, 2009; Park et al, 2010; Song et al, 2010), biogeochemical cycles We can highlight the empirical algorithms that are obtained through the relationship between optical measurements and the concentrations of constituents sampled in situ, and the semi-analytical algorithms, developed through theoretical mathematical formulations with statistical adjustments (IOCCG, 2000)

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