MeqTrees and direction-dependent effects

Abstract

Direction-dependent effects (DDEs) represent a major challenge both for calibration of new radio telescopes, and for advancing the state of the art of existing ones. Various approaches to the problem are currently in development. This paper describes several WSRT observations where a pointing error -- commonly thought to be a major contributor to DDEs at higher frequencies -- was deliberately introduced. These observations were reduced using the MeqTrees package, using two different approaches to correct for DDEs: differential gain solutions, and a direct solution for pointing errors. The results of this are analysed and compared.