Methods of performing surface profilometry are provided. A low coherence light beam is scanned relative to a sample surface. The intensity of interference fringes generated by the interference of a sample beam and a reference beam are recorded by an image sensor. Variations of light intensity around each pixel are calculated in terms of variance or standard derivation. The peak position of variance on a particular location along vertical scan direction is identified as the scan position corresponding to zero optical path difference between the reference and measuring beams. A topography map (height map) may be generated using the relative scanning position where zero optical path difference occurs at each location on sample surface.