Probing Ionospheric Structures using the LOFAR radio telescope

Abstract

LOFAR is the LOw Frequency Radio interferometer ARray located at mid-latitude ($52^{\circ }53^{\prime }N$). Here, we present results on ionospheric structures derived from 29 LOFAR nighttime observations during the winters of 2012/2013 and 2013/2014. We show that LOFAR is able to determine differential ionospheric TEC values with an accuracy better than 1 mTECU over distances ranging between 1 and 100 km. For all observations the power law behavior of the phase structure function is confirmed over a long range of baseline lengths, between $1$ and $80$ km, with a slope that is in general larger than the $5/3$ expected for pure Kolmogorov turbulence. The measured average slope is $1.89$ with a one standard deviation spread of $0.1$. The diffractive scale, i.e. the length scale where the phase variance is $1\mathrm{ra}{\mathrm{d}}^2$, is shown to be an easily obtained single number that represents the ionospheric quality of a radio interferometric observation. A small diffractive scale is equivalent to high phase variability over the field of view as well as a short time coherence of the signal, which limits calibration and imaging quality. For the studied observations the diffractive scales at $150$ MHz vary between $3.5$ and $30$ km. A diffractive scale above $5$ km, pertinent to about $90\%$ of the observations, is considered sufficient for the high dynamic range imaging needed for the LOFAR Epoch of Reionization project. For most nights the ionospheric irregularities were anisotropic, with the structures being aligned with the Earth magnetic field in about $60\%$ of the observations.

arXiv commentaccepted for publication in Radio Science

References in corpus (10)

• LOFAR: The LOw-Frequency ARray
• Ionospheric Calibration of Low Frequency Radio Interferometric Observations using the Peeling Scheme: I. Method Description and First Results
• Post-correlation radio frequency interference classification methods
• Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism
• The LOFAR radio environment
• Probing Fine-Scale Ionospheric Structure with the Very Large Array Radio Telescope
• Scintillation noise in widefield radio interferometry
• Power spectrum analysis of ionospheric fluctuations with the Murchison Widefield Array
• A New Technique for Spectral Analysis of Ionospheric TEC Fluctuations Observed with the Very Large Array VHF System: From QP Echoes to MSTIDs
• Ionospheric Power-Spectrum Tomography in Radio Interferometry

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