Correlation Properties of a 2-D Array of High Latitude Scintillation Receivers

Short-term signal fading and rapid phase changes can occur when the Global Navigation Satellite Systems (GNSS) signals pass through regions of ionospheric irregularities of scale sizes around tens to hundreds of meters [1]. At high latitudes, phase scintillations are observed more often than amplitude scintillations and are due to a variety of physical instability mechanisms in both the E and F regions of the ionosphere. When the ionosphere is irregular, diffractive scintillations will occur. The temporal behavior of diffractive scintillations depends on the Fresnel length of the scintillations, the drift speed of the ionosphere, and the relative velocities of the satellites and receivers [2]. There have been a number of significant high latitude studies of scintillation using the Global Positioning System (GPS), e.g., [3]. Most GPS high latitude scintillation studies were made with single GPS scintillation receivers or a network with baselines of 100s of kilometers, and therefore were not able to investigate the local spatial spectrum of the irregularities or the drift speeds. Scintillation studies for arrays around km scale baselines have been developed by [4] and more recently for an array for polar scintillations [5]. We build on this previous body of work with the beginning of an in-depth study of the spatial-temporal properties of GPS scintillations in the auroral oval region using a multi-receiver array deployed near the equatorial boundary of the auroral region and the night-side transition region. In late 2012, a test array of ASTRA Connected Autonomous Space Environment Sensors (CASES) was installed around the University of Calgary. These receivers stream one minute averages of scintillation parameters (S4 and sigma_phi), as well as high-rate I and Q samples to a server. From this test array, a final 7 receiver array is deployed in Canada at a location near the equatorial auroral boundary. This array is used to study the space-time properties of ionospheric irregularities that cause scintillations, through forward modeling and inverse diffraction tomography methods. In order to make such studies, we establish a scintillation event database. The database is based upon a “quick-look” set of scintillation data across the array, choosing both non-scintillating periods as baseline cases, and scintillating periods. The criteria for events being entered into the database are: • Significant scintillation on all receivers. • All-sky imagers observe significant auroral structuring [6]. • The GPS lines of sight (LOS) pass through the spatial region of the auroral structuring. • Location of the auroral boundary with respect to the scintillating LOS is estimated. The database is then used to choose periods for more in depth study of ionospheric irregularities by analysis of the high-rate I and Q data across the array. The results of this analysis will improve our understanding of the space-time distribution of ionospheric irregularities, the large scale drivers that cause the development of irregularities, and the nowcast and forecast of scintillations for GNSS systems. This paper focuses upon initial results from the array of scintillation receivers, including estimation of drift velocities from cross-correlations, estimation of the spectrum of irregularities, and geophysical conditions that caused the scintillations. [1] Morrissey, T.N., K. W. Shallberg, A. J. Van Dierendonck, and M. J. Nicholson (2004), GPS receiver performance characterization under realistic ionospheric phase scintillation environments, Radio Sci., vol. 39, pp. 1–18. [2] Kintner, P. M., B. M. Ledvina, E. R. de Paula, and I. J. Kantor (2004), Size, shape, orientation, speed, and duration of GPS equatorial anomaly scintillations, Radio Sci., 39, RS2012, doi:10.1029/2003RS002878. [3] Skone S., M. Feng, R. Tiwari and A. Coster (2009), Characterizing ionospheric irregularities for auroral scintillations, Proceedings of the 22nd International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 2551-2558. [4] Grzesiak M., and A.W. Wernik (2009), Dispersion analysis of spaced antenna scintillation measurement Ann. Geophys., 27, 2843–2849. [5] Wang, J., Morton, Y., Zhou, Q., Pelgrum, W., Spatial Characterization of High Latitude Ionosphere Scintillations, Proceedings of the 25th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. -. [6] Smith, A. M., C. N. Mitchell, R. J. Watson, R. W. Meggs, P. M. Kintner, K. Kauristie, and F. Honary (2008), GPS scintillation in the high arctic associated with an auroral arc, Space Weather, 6, S03D01, doi:10.1029/2007SW000349.

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