A radiative transfer model designed for application to snow-covered sea ice with vertical layering is presented which removes several of the computational problems associated with media whose optical properties are strong functions of wavelength and depth. With this model it is possible to treat the effects of biological activity in the ice as well as vertical variations in brine volume and bubble density. Transmission spectra can also be calculated as a function of depth in the water column beneath the ice. Accurate results are achieved for both direct and diffuse incident irradiance for single scattering albedos ranging from 0.0 to 0.99999999. Calculated albedos and extinction coefficients for snow and sea ice are consistent with both observations and previous models, and the model results resolve apparent inconsistencies among certain observational data sets. Refraction is included for all layer interfaces and is found to reduce the albedo, while the transmissivity responds to changes in the optical depth in addition to redirection of the radiation. For bare sea ice, ignoring refraction can introduce albedo errors as great as 24% and transmissivity errors of more than 70%. Absorption by algae in the ice is shown to reduce the transmitted radiation by more than a factor of 10 at certain visible wavelengths. The predicted azimuthal dependence of the emergent radiances is very weak even for large solar incidence angles. ¿American Geophysical Union 1991