Using Radio Telescopes to Probe the Ionosphere

New radio telescopes being developed for low frequency observing have to contend with refraction of the incoming radiation by the ionosphere. Radio astronomers have developed several methods by which to compensate for the turbulence of the ionospheric layers and the effect these have on the phase of the interferometer measurements. Understanding the distribution of disturbances is needed to determine the precision of new and upcoming experiments. The Precision Array to Probe the Epoch of Reionization is an experiment designed to detect the power spectrum of the epoch of reionization signal, an important step in observational cosmology. Our initial work with a prototype array is also used to probe the size distribution of ionosphere irregularities, using the positions of bright sources and tracking them over short timescales. We find that refraction on the order of an arcminute is common, with small fluctuations present over several minute timescales. This is compared to a simple model of the ionosphere to determine the isoplanatic patch size.