ic_set_tau valueThe optical thickness defined here is the integral from the surface at the user-defined altitude to TOA (top of atmosphere). This option is useful only for monochromatic calculations or in wavelength regions where the optical properties of ice clouds can be considered constant, e.g. the ultraviolet region. If you use this option in combination with the ice cloud properties by Fu (1996), please make sure that you understand the explanation of ic_fu_tau.