On the estimate and assessment of the ionospheric effects affecting low frequency radio astronomy measurements

The development of the LOw Frequency telescopes ARray (LOFAR) has posed a serious issue on the calibration of those measurements in the presence of the Earth´s ionosphere. The purpose of measuring at radio frequencies as low as VHF exposes LOFAR to a number of ionospheric phenomena, capable of deteriorating the accuracy of the measurements and subsequently of the sky imaging. The ionosphere is normally treated at signal processing level, where various efforts attempt to remove possible errors introduced by it. Here, a close look at particular ionospheric features and their possible consequence to radio astronomy measurements is given from a point of view of the ionospheric radio wave propagation. It seems the radio astronomy and ionosphere communities will need to work closely together in order to achieve a satisfactory solution to the problem.