Estimation of the spectral diffuse attenuation coefficient Kd(λ) from UV to NIR using ocean color images: Application from SeaWiFS to PACE

The fine-scale study of the diffuse attenuation coefficient, K_d(l), of the spectral solar downward irradiance  is only feasible by ocean color remote sensing. Several empirical and semi-analytical methods exist. However, most of these models are generally applicable for clear open ocean waters. They show limitations when applied to coastal waters. A new empirical method based on neural networks has been developed using a relationship between the remote-sensing reflectances between 443 and 670 nm and K_d(λ). The architecture of the neural network has been defined using synthetical and in situ dataset. The model has been developed for SeaWiFS, MODIS-AQUA, MERIS, VIIRS, OLCI and PACE space-borne sensors. Validation using in-situ measurements from a wide range of type of waters (from oligotrophic to very turbid waters) shows similar retrievals accuracies for low values of K_d(490)  (i.e. <0.20 m^-1) and better estimates for greater values of and K_d(490). The new model is compared to empirical and semi-empirical methods and is suitable for open water but also for turbid waters.