An inherent-optical-property-centered approach to correct the angular effects in water-leaving radiance

Remote-sensing reflectance (R_rs), which is defined as the ratio of water-leaving radiance (L_w) to downwelling irradiance just above the surface (E_d(0⁺)), varies with both water constituents (including bottom properties of optically-shallow waters) and angular geometry. L_w is commonly measured in the field or by satellite sensors at convenient angles, while E_d(0⁺) can be measured in the field or estimated based on atmospheric properties. To isolate the variations of R_rs (or L_w) resulting from a change of water constituents, the angular effects of R_rs (or L_w) need to be removed. This is also a necessity for the calibration and validation of satellite ocean color measurements. To reach this objective, for optically-deep waters where bottom contribution is negligible, we present a system centered on water's inherent optical properties (IOPs). It can be used to derive IOPs from angular R_rs and offers an alternative to the system centered on the concentration of chlorophyll. This system is applicable to oceanic and coastal waters as well as to multiband and hyperspectral sensors. This IOP-centered system is applied to both numerically simulated data and in situ measurements to test and evaluate its performance. The good results obtained suggest that the system can be applied to angular R_rs to retrieve IOPs and to remove the angular variation of R_rs.