An Eigenvector-based Method of Radio Array Calibration and Its Application to the Tianlai Cylinder Pathfinder

TL;DR

This paper introduces an eigenvector-based calibration method for radio interferometer arrays, utilizing stable principal component analysis to improve initial calibration accuracy, especially in the presence of outliers and poor beam knowledge.

Contribution

The paper presents a novel eigenvector-based calibration technique combined with SPCA, suitable for initial array calibration with low computational complexity and robustness to data imperfections.

Findings

Successfully calibrated Tianlai cylinder pathfinder array using the proposed method.

Achieved accurate estimation of array gains and beam profiles from transit data.

Method is robust to outliers and does not require precise beam models.

Abstract

We propose an eigenvector-based formalism for the calibration of radio interferometer arrays. In the presence of a strong dominant point source, the complex gains of the array can be obtained by taking the first eigenvector of the visibility matrix. We use the stable principle component analysis (SPCA) method to help separate outliers and noise from the calibrator signal to improve the performance of the method. This method can be applied with poorly known beam model of the antenna, and is insensitive to outliers or imperfections in the data, and has low computational complexity. It thus is particularly suitable for the initial calibration of the array, which can serve as the initial point for more accurate calibrations. We demonstrate this method by applying it to the cylinder pathfinder of the Tianlai experiment, which aims to measure the dark energy equation of state using the baryon acoustic oscillation (BAO) features in the large scale structure by making intensity mapping observation of the redshifted 21~cm emission of the neutral hydrogen (HI). The complex gain of the array elements and the beam profile in the East-West direction (short axis of the cylinder) are successfully obtained by applying this method to the transit data of bright radio sources.