Sinusoidal wavelength-scanning (SWS) interferometry is unique in that a time-varying interference signal contains phase-modulation amplitude Z b due to the SWS besides a conventional phase α. Propagation time and wavefront of the light wave diffusely reflected from a metal surface can be detected from the amplitude Zb and the phase α, respectively. A concave shape with the depth of about a few hundreds microns is measured with an error less than a few microns by using only the amplitude Zb of the detected interference signal. © 2012 SPIE.