Characterisation of the ionosphere above the Murchison Radio Observatory using the Murchison Widefield Array

TL;DR

This paper introduces new techniques for analyzing ionospheric activity using high-resolution data from the Murchison Widefield Array, identifying distinct activity types and developing real-time calibration metrics applicable to other radio telescopes.

Contribution

The study presents novel methods for characterizing ionospheric activity, including a data quality metric, analysis of activity types, and a reconstruction technique, applicable across multiple radio observatories.

Findings

Four distinct ionospheric activity types identified.

A metric for data quality under varying ionospheric conditions developed.

Real-time calibration of ionospheric phase screens demonstrated.

Abstract

We detail new techniques for analysing ionospheric activity, using Epoch of Reionisation (EoR) datasets obtained with the Murchison Widefield Array (MWA), calibrated by the `Real-Time System' (RTS). Using the high spatial- and temporal-resolution information of the ionosphere provided by the RTS calibration solutions over 19 nights of observing, we find four distinct types of ionospheric activity, and have developed a metric to provide an `at a glance' value for data quality under differing ionospheric conditions. For each ionospheric type, we analyse variations of this metric as we reduce the number of pierce points, revealing that a modest number of pierce points is required to identify the intensity of ionospheric activity; it is possible to calibrate in real-time, providing continuous information of the phase screen. We also analyse temporal correlations, determine diffractive scales, examine the relative fractions of time occupied by various types of ionospheric activity, and detail a method to reconstruct the total electron content responsible for the ionospheric data we observe. These techniques have been developed to be instrument agnostic, useful for application on LOFAR and SKA-Low.