Deriving the Vertical Variations in the Diffuse Attenuation Coefficient of Photosynthetically Available Radiation in the North Pacific Ocean from Remote Sensing

Diffuse attenuation coefficient of photosynthetically available radiation (PAR), K-PAR, is a key product of ocean color remote sensing. Current ocean color algorithms generally detect only the average K-PAR within one optical depth, K-PAR(RS). Due to the marked vertical variations of K-PAR, knowledge of K-PAR(RS) is insufficient to accurately evaluate the submarine light field. By using field in situ observations, a two-step approach, based on the development of an ocean color algorithm for K-PAR(RS) and the relationships between K-PAR(RS) and the average K-PAR from the surface down to depth Z ((K) over bar (Z)(PAR)), was developed to remotely estimate the vertical variations in (K) over bar (Z)(PAR) in the North Pacific from the MODerate-resolution Imaging Spectrometer (MODIS) imagery. The root mean square difference of log((K) over bar (Z)(PAR)) in depths within the euphotic zone was around +/- 0.059 (in unit of m(-1) for (K) over bar (Z)(PAR)), which corresponded to a deviation of +/- 15% for the estimated (K) over bar (Z)(PAR) and the penetration depths of PAR. Our study may provide a promising approach to detect the vertical variations of (K) over bar (Z)(PAR) and underwater PAR distributions in the North Pacific Ocean.