With object of determining the atmospheric turbidity (aerosol optical depth) from upward emerging spectral radiances, an evaluation was made of that wavelength at which the variability of the radiance owing to the variability of the turbidity predominates the variability caused by the the perturbing optical parameters. This has been done by numerical modeling of the variability of the radiances owing to the variability of all optically acting atmospheric constituents (no clouds) and the underlying rough ocean for maritime aerosols and Saharan dust. It is found that the optimum wavelengths are 0.75 and 0.87 μm. In addition, it has been found that low sun and low observation elevation angles are preferable.