Abstract:
Phases in interferometry are a key element to reconstructing the source properties. There are several situations when the phases are poorly constrained due to corrupting effects in the propagation medium and/or the instrument, or not constrained at all. Examples include radio interferometry, X-ray crystallography, seismology, etc. Image reconstruction in these situations have been critically helped by a special class of phases (called closure phases in radio interferometry) that are preserved despite the phase corruptions introduced during the measurement process and therefore encode true morphological information about the object of interest. I will discuss the geometric interpretation of closure phase and its invariance, which until recently had remained unclear.