Limits on the validity of the thin-layer model of the ionosphere for radio interferometric calibration

TL;DR

This paper evaluates the limitations of the thin-layer model used in radio interferometry calibration, providing a simple equation to determine its applicability under various observational conditions.

Contribution

The authors analyze the validity of the thin-layer ionospheric model and derive a practical equation to assess its suitability for different observational parameters.

Findings

The thin-layer model has specific validity conditions based on observational parameters.

A simple equation is provided to check the model's applicability.

The model's limitations depend on factors like frequency, baseline, and ionospheric conditions.

Abstract

For a ground-based radio interferometer observing at low frequencies, the ionosphere causes propagation delays and refraction of cosmic radio waves which result in phase errors in the received signal. These phase errors can be corrected using a calibration method that assumes a two-dimensional phase screen at a fixed altitude above the surface of the Earth, known as the thin-layer model. Here we investigate the validity of the thin-layer model and provide a simple equation with which users can check when this approximation can be applied to observations for varying time of day, zenith angle, interferometer latitude, baseline length, ionospheric electron content and observing frequency.