Phases in interferometry

While interference fringes contain both amplitude and phase information, most interferometric results published to date focus solely on the amplitude data. This is because atmospheric turbulence corrupts the observed fringe phases, rendering them almost useless by themselves. Various techniques can be used to recover phase information and in this chapter we discuss the techniques of narrow-angle astrometry, differential phase, and phase closure for effectively recovering valuable and unique science from the otherwise-scrambled phase measurements. We focus especially on applications of closure phase made possible by current facilities.