The MeqTrees software system and its use for third-generation calibration of radio interferometers

TL;DR

MeqTrees is a flexible, high-performance software system that implements the radio interferometer measurement equation for advanced calibration of next-generation radio telescopes like LOFAR and SKA.

Contribution

It introduces a Python-based front-end and C++ back-end for rapid modeling and calibration, specifically designed for third-generation radio interferometry.

Findings

Achieved noise-limited dynamic range over a million with WSRT data

Demonstrated suitability for third-generation calibration of large radio telescopes

Supported simulation and calibration for LOFAR and SKA instruments

Abstract

The formulation of the radio interferometer measurement equation (RIME) by Hamaker et al. has provided us with an elegant mathematical apparatus for better understanding, simulation and calibration of existing and future instruments. The calibration of the new radio telescopes (LOFAR, SKA) would be unthinkable without the RIME formalism, and new software to exploit it. MeqTrees is designed to implement numerical models such as the RIME, and to solve for arbitrary subsets of their parameters. The technical goal of MeqTrees is to provide a tool for rapid implementation of such models, while offering performance comparable to hand-written code. We are also pursuing the wider goal of increasing the rate of evolution of radio astronomical software, by offering a tool for rapid experimentation and exchange of ideas. MeqTrees is implemented as a Python-based front-end called the meqbrowser, and an efficient (C++-based) computational back-end called the meqserver. Numerical models are defined on the front-end via a Python-based Tree Definition Language (TDL), then rapidly executed on the back-end. The use of TDL facilitates an extremely short turn-around time for experimentation with new ideas. This is also helped by unprecedented visualization capabilities for all final and intermediate results. A flexible data model and a number of important optimizations in the back-end ensures that the numerical performance is comparable to that of hand-written code. MeqTrees is already widely used as the simulation tool for new instruments (LOFAR, SKA) and technologies (focal plane arrays). It has demonstrated that it can achieve a noise-limited dynamic range in excess of a million, on WSRT data. It is the only package that is specifically designed to handle what we propose to call third-generation calibration (3GC), which is needed for the new generation of giant radio telescopes.