Set the total ice cloud optical depth to a constant value for all wavelengths.
ic_set_tau value
The 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 Fu1996, please make sure that you understand
the explanation of ic_fu_tau.