Wavelet Analysis of Differential TEC Measurements Obtained Using LOFAR

Abstract

Radio interferometers used to make astronomical observations, such as the LOw Frequency ARray (LOFAR), experience distortions imposed upon the received signal due to the ionosphere as well as those from instrumental errors. Calibration using a well-characterised radio source can be used to mitigate these effects and produce more accurate images of astronomical sources, and the calibration process provides measurements of ionospheric conditions over a wide range of length scales. The basic ionospheric measurement this provides is differential Total Electron Content (TEC, the integral of electron density along the line of sight). Differential TEC measurements made using LOFAR have a precision of <1 mTECu and therefore enable investigation of ionospheric disturbances which may be undetectable to many other methods. We demonstrate an approach to identify ionospheric waves from these data using a wavelet transform and a simple plane wave model. The noise spectra are robustly characterised to provide uncertainty estimates for the fitted parameters. An example is shown in which this method identifies a wave with an amplitude an order of magnitude below those reported using GNSS TEC measurements. Artificially generated data are used to test the accuracy of the method and establish the range of wavelengths which can be detected using this method with LOFAR data. This technique will enable the use of a large and mostly unexplored dataset to study travelling ionospheric disturbances over Europe.

Authors 8

1. Ben Boyde

   University of Birmingham

   Affiliation as printed

   University of Birmingham

   Space Environment and Radio Engineering, School of Engineering, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK

2. Alan George Wood corresponding

   University of Birmingham

   Affiliation as printed

   University of Birmingham

   Space Environment and Radio Engineering, School of Engineering, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK

3. Gareth D. Dorrian

   University of Birmingham · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   University of Birmingham

   ASTRON -The Netherlands Institute for Radio Astronomy

   ASTRON -The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

   Space Environment and Radio Engineering, School of Engineering, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK

4. Frits Sweijen Aachen Leiden Observatory

   Leiden University · Universität Hamburg · Istituto di Radioastronomia di Bologna · Leiden Observatory · National Institute for Astrophysics · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   Leiden Observatory

   ASTRON -The Netherlands Institute for Radio Astronomy

   Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

   Institute of Radioastronomy (IRA-INAF)

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

5. F. de Gasperin

   Istituto di Radioastronomia di Bologna · University of Birmingham · National Institute for Astrophysics

   Affiliation as printed

   Institute of Radioastronomy (IRA-INAF)

   INAF -Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy

   Space Environment and Radio Engineering, School of Engineering, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK

   University of Birmingham

6. M. Mevius

   Universität Hamburg · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   astron

   Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

7. Kasia Beser

   Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON - The Netherlands Institute for Radio Astronomy

   ASTRON -The Netherlands Institute for Radio Astronomy

   ASTRON -The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

8. David R. Themens

   University of Birmingham

   Affiliation as printed

   University of Birmingham

   Space Environment and Radio Engineering, School of Engineering, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK