Peng Shi

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 (${\overline{K}}_{PAR}^Z$), was developed to remotely estimate the vertical variations in ${\overline{K}}_{PAR}^Z$ in the North Pacific from the MODerate-resolution Imaging Spectrometer (MODIS) imagery. The root mean square difference of log(${\overline{K}}_{PAR}^Z$) in depths within the euphotic zone was around ±0.059 (in unit of m⁻¹ for ${\overline{K}}_{PAR}^Z$), which corresponded to a deviation of ±15% for the estimated ${\overline{K}}_{PAR}^Z$ and the penetration depths of PAR. Our study may provide a promising approach to detect the vertical variations of ${\overline{K}}_{PAR}^Z$ and underwater PAR distributions in the North Pacific Ocean.