Ocean inherent optical property estimation from irradiances

A method is evaluated for estimating the absorption coefficient a and the backscattering coefficient b_b from measurements of the upward and downward irradiances E_u(z) and E_d(z). With this method, the reflectance ratio R(z) and the downward diffuse attenuation coefficient K_d(z) obtained from E_u(z) and E_d(z) are used to estimate the inherent optical properties R_∞ and K_∞ that are the asymptotic values of R(z) and K_d(z), respectively. For an assumed scattering phase function $\tilde{\mathrm{\beta }}$, there are unique correlations between the values of R_∞ and K_∞ and those of a and b_b that can be derived from the radiative transfer equation. Good estimates of a and the Gordon parameter G = b_b/(a + b_b) can be obtained from R_∞ and K_∞ if the true scattering phase function is not greatly different from the assumed function. The method works best in deep, homogeneous waters, but can be applied to some cases of stratified waters. To improve performance in shallow waters where bottom effects are important, the deep- and shallow-measurement reflectance models also are developed.