Estimation of Absorption and Backscattering Coefficients from in Situ Radiometric Measurements: Theory and Validation in Case II Waters

A model that relates the coefficients of absorption (a ) and backscattering (bb) to diffuse attenuation (Kd), radiance reflectance (RL), and the mean cosine for downward irradiance ((mu)d) is presented. Radiance transfer simulations are used to verify the physical validity of the model for a wide range of water column conditions. Analysis of these radiance transfer simulations suggests that absorption and backscattering can be estimated with average errors of 1% and 3%, respectively, if the value of (mu)d is known with depth. If the input data set is restricted to variables that can be derived from measurements of upward radiance (Lu) and downward irradiance (Ed), it is necessary to use approximate values of (mu)d . Examination of three different approximation schemes for (mu)d shows that the average error for estimating a and bb increases to ~13%. We tested the model by using measurements of Lu and Ed collected from case II waters off the west coast of Scotland. The resulting estimates of a and bb were compared with independent in situ measurements of these parameters. Average errors for the data set were of the order of 10% for both absorption and backscattering.