De-distorting ionospheric effects in the image plane

TL;DR

This paper introduces a method to correct ionospheric refraction effects in radio interferometric images, restoring source positions accurately across the image and catalogue domains, applicable when all antennas observe the same ionosphere.

Contribution

A novel, generalizable technique for removing ionospheric distortions from radio images and source catalogues, improving positional accuracy in interferometric observations.

Findings

Effective removal of ionospheric shifts demonstrated

Applicable to all antennas observing the same ionosphere

Open-source implementation available

Abstract

The Earth's ionosphere refracts radio waves incident on an interferometer, resulting in shifts to the measured positions of radio sources. We present a method to smoothly remove these shifts and restore sources to their reference positions, in both the catalogue and image domains. The method is applicable to instruments and ionospheric weather such that all antennas see the same ionosphere. The method is generalisable to repairing any sparsely-sampled vector field distortion to some input data. The code is available under the Academic Free License (https://opensource.org/licenses/AFL-3.0) from https://github.com/nhurleywalker/fits_warp