Exploring Earth's Ionosphere and its effect on low radio frequency observation with the uGMRT and the SKA

TL;DR

This study characterizes ionospheric disturbances affecting low-frequency radio observations using GMRT and compares them with other telescopes, providing insights for future SKA observations during geomagnetic activities.

Contribution

It presents a detailed analysis of ionospheric effects on low-frequency radio telescopes and forecasts their impact on future SKA observations based on multi-telescope data.

Findings

Ionospheric TEC gradients are an order of magnitude higher than GNSS measurements.

Significant ionospheric activities are observed even during solar minimum.

Comparative analysis with other telescopes enhances understanding of ionospheric effects.

Abstract

The Earth's ionosphere introduces systematic effects that limit the performance of a radio interferometer at low frequencies ($\lesssim 1$\,GHz). These effects become more pronounced for severe geomagnetic activities or observations involving longer baselines of the interferometer. The uGMRT, a pathfinder for the Square Kilometre Array (SKA), is located in between the northern crest of the Equatorial Ionisation Anomaly (EIA) and the magnetic equator. Hence, this telescope is more prone to severe ionospheric conditions and is a unique radio interferometer for studying the ionosphere. Here, we present 235\,MHz observations with the GMRT, showing significant ionospheric activities over a solar minimum. In this work, we have characterised the ionospheric disturbances observed with the GMRT and compared them with ionospheric studies and observations with other telescopes like the VLA, MWA and LOFAR situated at different magnetic latitudes. We have estimated the ionospheric total electron content (TEC) gradient over the full GMRT array which shows an order of magnitude higher sensitivity compared to the Global Navigation Satellite System (GNSS). Furthermore, this article uses the ionospheric characteristics estimated from the observations with uGMRT, VLA, LOFAR and MWA to forecast the effects on the low-frequency observations with the SKA1-MID and SKA1-LOW in future.