1. A method, comprising: directing measurement light to reflect from a measurement surface; combining the reflected measurement light with reference light, wherein the measurement light and reference light are derived from a common source, and there is a non-zero optical path length difference between the measurement light and reference light that is greater than a coherence length of the measurement light; spectrally dispersing the combined light onto a multi-element detector to detect a spatially-varying intensity pattern; determining spatial information about the measurement surface based on the spatially-varying intensity pattern; and outputting the spatial information.