Simple analytical formulae are presented to calculate the local optical parameters and the spherical albedo r of close-packed media with large particles. The formulae obtained can be used to describe recent experiments on snow and foam optics. It was found that the value of r of weak absorbing semi-infinite layers with large particles depends mostly on two parameters (the effective size of particles and the imaginary part of their refractive index). Another important characteristic is the absorption coefficient of low-level contaminants (soot, dust particles, detergents in foam). This value determines the spherical albedo of snow and foam in the visible. The accuracy of obtained equations is better than 10% at r>0.2. ¿ 1998 American Geophysical Union