An optical scanning system and method for detecting anomalies, including pattern defects and particulate contaminants, on both patterned and unpatterned surfaces, using a light beam, scanning at a grazing angle with respect to the surfaces, a plurality of detectors and an interchannel communication scheme to compare data from each detector, which facilitates characterizing anomalies. The light beam illuminates a spot on the surface which is scanned over a short scan-line. The surface is moved in a manner so that the spot is scanned over its entire area in a serpentine fashion along adjacent striped regions. The plurality of detectors include groups of collector channels disposed circumferentially around the surface, a bright field reflectivity/autoposition channel, an alignment/registration channel and an imaging channel. The collector channels in each group are symmetrically disposed, in the azimuth, on opposite sides of the center of the scan line. The position of the collector channels, as well as the polarization of the beam, facilitates distinguishing pattern defects from particulate contaminants. The bright field reflectivity/autoposition channel is positioned to receive specularly reflected light that carries information concerning local variation in reflectivity, which is used to classify detected anomalies, as well as determine variations in the height of the surface. The alignment/registration channel is positioned to detect a maximum of the light scattered from the pattern on the surface to ensure that the streets of die present on the surface are oriented so as not to be oblique with respect to the scan line. The imaging channel combines the advantages of a scanning system and an imaging system while improving signal/background ratio of the present system.