Generalized redundant calibration of radio interferometers

Abstract

Redundant calibration is a technique in radio astronomy that allows calibration of radio arrays whose antennas lie on a lattice by exploiting the fact that redundant baselines should see the same sky signal. Because the number of measured visibilities scales quadratically with the number of antennas but the number of unknowns describing the individual antenna responses and the available information about the sky scales only linearly with the array size, the problem is always overconstrained as long as the array is big and dense enough. This is true even for nonlattice array configurations. In this work we study a generalized algorithm in which a per-antenna gain is replaced with a number of gains. We show that it can successfully fit data from an approximately redundant array on square lattice with pointing and geometry errors, but that the model's parameters are difficult to link to the quantities of interest. We discuss the parametrization, limitations, and possible extensions of this algorithm.