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

Abstract

A performance evaluation of ocean color chlorophyll-a algorithms was conducted based on the in situ fluorescence chlorophyll concentration (F_chl) 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 (C_sat). F_chl 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 F_chl values into chlorophyll concentration (C_flu). Overall, linear regression analysis between C_flu and C_sat 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.

Descriptors:
Ocean color; MODIS; VIIRS; Southern Brazilian Coastal Waters; in situ fluorescence chlorophyll-a; moored measurements