1. A method of determining physical information about a test object surface, the method comprising: obtaining, from a scanning interferometry device, scanning interferometry data for a surface of the test object; calculating a coherence profile of the surface of the test object and a phase profile of the surface of the test object based on the scanning interferometry data; calculating a phase gap map based on the coherence profile and the phase profile; modifying, using an electronic processor, the coherence profile based on the phase gap map to obtain a corrected coherence profile; and determining the information about the surface of the test object based on the corrected coherence profile.