Ionospheric Modelling using GPS to Calibrate the MWA. I: Comparison of First Order Ionospheric Effects between GPS Models and MWA Observations

Arora, B. S.; Morgan, John S.; Ord, S. M.; Tingay, S. J.; Hurley‐Walker, N.; Bell, M. E.; Bernardi, G.; Briggs, F.; Callingham, J. R.; Deshpande, A. A.; Dwarakanath, K. S.; Ewall‐Wice, Aaron; Lü, Feng; For, Bi-Qing; Hancock, P. J.; Hazelton, B. J.; Hindson, L.; Jacobs, Daniel; Johnston‐Hollitt, M.; Kapińska, A. D.; Kudryavtseva, N. A.; Lenc, E.; McKinley, B.; Mitchell, D. A.; Oberoi, D.; Offringa, A. R.; Pindor, B.; Procopio, P.; Riding, J.; Wayth, R. B.; Wu, Chen; Zheng, Qian; Bowman, Judd D.; Cappallo, R. J.; Corey, B. E.; Emrich, D.; Goeke, R.; Greenhill, L. J.; Kaplan, David L.; Kasper, J. C.; Kratzenberg, E.; Lonsdale, Colin J.; Lynch, M. J.; McWhirter, S. R.; Morales, M. F.; Morgan, E.; Prabu, T.; Rogers, A. E. E.; Roshi, A.; Shankar, N. Udaya; Srivani, K. S.; Subrahmanyan, R.; Waterson, M.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, Christopher

doi:10.1017/pasa.2015.29

Cited by 17 publications

(21 citation statements)

References 41 publications

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“…COMPARING IONOSPHERIC RM OUTPUTS There are now several software packages that interpret CODE ionex files specifically for the use of low frequency radio interferometers. Two of these are ionFR (Sotomayor-Beltran et al 2013) and the results shown in (Arora et al 2015). In Figure 19 we show qualitative agreement with both of these works by comparing maps of vertical TEC values over the globe.…”

Section: Appendixsupporting

confidence: 80%

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Ionospheric Attenuation of Polarized Foregrounds in 21 cm Epoch of Reionization Measurements: A Demonstration for the HERA Experiment

Martinot

Aguirre

Kohn

et al. 2018

ApJ

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Foregrounds with polarization states that are not smooth functions of frequency present a challenge to Hi Epoch of Reionization (EoR) power spectrum measurements if they are not cleanly separated from the desired Stokes I signal. The intrinsic polarization impurity of an antenna's electromagnetic response limits the degree to which components of the polarization state on the sky can be separated from one another, leading to the possibility that this frequency structure could be confused for Hi emission. We investigate the potential of Faraday rotation by the Earth's ionosphere to provide a mechanism for both mitigation of, and systematic tests for, this contamination. Specifically, we consider the delay power spectrum estimator, which relies on the expectation that foregrounds will be separated from the cosmological signal by a clearly demarcated boundary in Fourier space, and is being used by the Hydrogen Epoch of Reionization Array (HERA) experiment. Through simulations of visibility measurements which include the ionospheric Faraday rotation calculated from real historical ionospheric plasma density data, we find that the incoherent averaging of the polarization state over repeated observations of the sky may attenuate polarization leakage in the power spectrum by a factor of 10 or more. Additionally, this effect provides a way to test for the presence of polarized foreground contamination in the EoR power spectrum estimate.

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Section: Appendixsupporting

confidence: 80%

“…Slight offsets at the highest RM values that day can be attributed to differences in our interpolation schemes. 2013), as pointed-out by Arora et al (2015). Figure 20.…”

Section: Appendixmentioning

confidence: 54%

Ionospheric Attenuation of Polarized Foregrounds in 21 cm Epoch of Reionization Measurements: A Demonstration for the HERA Experiment

Martinot

Aguirre

Kohn

et al. 2018

ApJ

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“…The ionosphere has been studied for many decades, typically with ionosondes, but also using global position system (GPS) satellites at coarse resolution (temporally 2 hours, spatially 5 • and 2.5 • in longitude and latitude, respectively; Arora et al 2015). Such study has determined that the electron density of the ionosphere is most significant at altitudes between 150 and several thousand kilometres, although it peaks between 250 and 600 km (Mannucci et al 1998).…”

Section: The Ionospherementioning

confidence: 99%

Characterization of the ionosphere above the Murchison Radio Observatory using the Murchison Widefield Array

Jordan

Murray

Trott

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We detail new techniques for analysing ionospheric activity, using Epoch of Reionisation (EoR) datasets obtained with the Murchison Widefield Array (MWA), calibrated by the 'Real-Time System' (RTS). Using the high spatial-and temporal-resolution information of the ionosphere provided by the RTS calibration solutions over 19 nights of observing, we find four distinct types of ionospheric activity, and have developed a metric to provide an 'at a glance' value for data quality under differing ionospheric conditions. For each ionospheric type, we analyse variations of this metric as we reduce the number of pierce points, revealing that a modest number of pierce points is required to identify the intensity of ionospheric activity; it is possible to calibrate in real-time, providing continuous information of the phase screen. We also analyse temporal correlations, determine diffractive scales, examine the relative fractions of time occupied by various types of ionospheric activity, and detail a method to reconstruct the total electron content responsible for the ionospheric data we observe. These techniques have been developed to be instrument agnostic, useful for application on LOFAR and SKA-Low.

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“…A systematic study of ionospheric conditions at the MRO site and correlations with bulk ionosphere statistics at higher frequencies is currently underway (Loi et al, in preparation). Studies incorporating information from ancillary probes such as GPS stations are also being carried out (Arora et al 2015).…”

Section: Ionospheric Contaminationmentioning

confidence: 99%

First limits on the 21 cm power spectrum during the Epoch of X-ray heating

Ewall‐Wice

Dillon

Hewitt

et al. 2016

Mon. Not. R. Astron. Soc.

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104

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We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). Three hours of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1-3 hours of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of 10 4 mK on comoving scales k 0.5 hMpc −1 . This represents the first upper limits on the 21 cm power spectrum fluctuations at redshifts 12 z 18 but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window.

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Ionospheric Modelling using GPS to Calibrate the MWA. I: Comparison of First Order Ionospheric Effects between GPS Models and MWA Observations

Cited by 17 publications

References 41 publications

Ionospheric Attenuation of Polarized Foregrounds in 21 cm Epoch of Reionization Measurements: A Demonstration for the HERA Experiment

Ionospheric Attenuation of Polarized Foregrounds in 21 cm Epoch of Reionization Measurements: A Demonstration for the HERA Experiment

Characterization of the ionosphere above the Murchison Radio Observatory using the Murchison Widefield Array

First limits on the 21 cm power spectrum during the Epoch of X-ray heating

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