1. Apparatus for measuring diffuse backscattering of electromagnetic radiation from a medium, which comprises in combination: (a) a source of electromagnetic radiation having a chosen wavelength; (b) first polarizer means for receiving the electromagnetic radiation and for selectively polarizing the electromagnetic radiation; (c) means for directing the polarized electromagnetic radiation into a small area of the medium substantially perpendicular to the surface of the medium; (d) means for collecting multiply-scattered electromagnetic radiation emerging from the medium in the vicinity of the area of entry of the electromagnetic radiation into the medium and in the opposite direction to the direction of the incident electromagnetic radiation; (e) mask means for blocking specular reflection from the surface of the medium in the collected backward-scattered electromagnetic radiation; (f) second polarizer means for receiving the collected backward-scattered electromagnetic radiation and for selectively polarization analyzing the collected backward-scattered electromagnetic radiation; and (g) means for receiving the polarization-analyzed, collected backward-scattered electromagnetic radiation and simultaneously recording the spatial components of the intensity thereof.