Optical bandpass characteristics of reflectance from random media

Experiments show that the optical reflectance of a random medium can have a nonmonotonic dependence on wavelength even when its absorption spectrum is flat and its scattering coefficient decreases monotonically with wavelength. Measured at a particular radial distance from the illumination point, the reflectance is almost independent of wavelength over a wide band. The peak wavelength of the reflectance increases as the optical distance to the detector increases. We explain that this behavior is a consequence of the interplay between direct backscattered and diffuse photon fluxes, whose magnitudes at the surface of the medium have opposite dependencies on the mean scattering length. @S1063-651X~98!00805-8#