One of the key issues for ocean color investigation using Ocean Color Imager (OCI) radiance is the correction for atmospheric effect. In particular, the water-leaving radiance is an order of magnitude less than that of observed radiance, so the accuracy of the concentration of phytoplankton pigments retrieval depends on the accuracy of the correction of atmospheric effect. According to the magnitude of atmospheric effect, it is divided into three categories: the zero order, Rayleigh scattering; the first order, Mie scattering; the second order, including the effect of multi-scattering, polarization, sea surface roughness, viewing angle and the temporal and spatial variation of pressure and total ozone concentration. The Rayleigh scattering effect on OCI channels is the focus of this paper. The optical thickness of Rayleigh scattering and the transmittance of the atmosphere were calculated using 5 coastal surface data from the Taiwan area. The results show that the optical thickness of Rayleigh scattering and the transmittance of the atmosphere are significantly changed for various locations and seasons. To ensure that the atmospheric model can be used in operation, a model for providing Rayleigh scattering optical thickness and transmittance has been established using three-year surface data.
The daily and seasonal variations of Rayleigh scattering radiance were discussed. In daily variation, the results show that before noon the minimum regions of Rayleigh scattering radiance spread from the center to the edge in the Rayleigh radiance image and after noon the minimum regions of Rayleigh scattering radiance come together from the edge to the center. The reason for these phenomena may be caused by different solar zenith angles. In seasonal variation, it was found that the Rayleigh scattering radiance was significantly changed following the declination movement of the sun. Generally, the Rayleigh scattering radiance in winter is less than that in summer. In addition, the minimum value, the maximum value and the range of Rayleigh scattering radiance were discussed. In daily variation, the results indicate that among the maxima, the radiance at 8 A.M. is largest, and among the minima, the radiance at 10 A.M. is smallest, and that within the range the difference at 8 A.M. is largest, and at 10 A.M. is smallest. In seasonal variation, the results show that among the minima, January is largest and among the maxima, June is the smallest. The Rayleigh scattering radiance regularly increases from January to June and regularly decreases from June to December and the minimum range occurs in March and maximum range in June.