Abstract: The present invention is directed to a method and apparatus for nondestructively locating and identifying subsurface features of a material or structure. A thermographic scanner constructed in accordance with the invention includes a heat source passed over the surface of interest at a controlled speed and followed in a fixed, spaced-apart relation by an array of detectors. The heat source produces an enhanced temperature gradient on the surface that is a function of the subsurface features. The detectors respond to the surface temperature and produce an indication of the type of subsurface features present. The scanner is provided with wheels connected to an optical encoder that produces an indication of the scanner's position over the surface. Thus, the output of the optical encoder is used to indicate the location of the scanner and detectors with respect to the surface.