Abstract: A broadband interferometric vertical scan of a sample surface is performed to produce interference data in conventional manner. A coarse surface profile of the surface is obtained in real time using a conventional technique, such as a center-of-mass calculation. A fine surface map is obtained concurrently using a quadrature-demodulation algorithm applied in real time to the same interference data used for the coarse surface calculation. The fine surface map is then combined with the coarse surface profile using an unwrapping technique that produces a final surface map with sub-nanometer resolution within a large height range.