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Lookup NU author(s): Dr Rajesh TiwariORCiD
GPS is a satellite-based radio navigation system, with diverse applications such as surveying, enroute navigation and precision approach of aircraft, deformation monitoring, and land/marine navigation. Many such applications require very high levels of accuracy, reliability and availability. A challenge to such applications exists, however, during high levels of ionospheric activity. The GPS signals are refracted by an amount dependent on the given signal frequency and total electron content along the signal path. In regions of small-scale irregularities in electron density the GPS signals may experience scintillation effects – random rapid variations in signal phase and amplitude. Such effects can cause errors in receiver signal tracking loops and, in some cases, loss of signal lock. Ionospheric scintillations occur primarily in the equatorial, auroral and polar regions. In each region there are different physical processes leading to formation of electron density irregularities. For example, the polar cap is a region of magnetic field lines open to the solar wind; polar patches of ions and electrons can form and convect over the pole in the anti-sunward direction. In steep gradients at the edges of these patches, gradient-drift instabilities can develop with associated small-scale irregularities and scintillation effects. GPS signals propagating through the polar cap can experience both phase and amplitude scintillation effects. In the auroral oval, strong phase scintillation effects are observed when energetic electrons precipitate into the night side ionosphere along closed magnetic field lines during substorm events; amplitude scintillations are minimal in this region. Since 2003 the University of Calgary has operated a number of specialized GPS receivers in Canada for ionosphere monitoring – as part of the CANGIM (CANadian GPS Network for Ionosphere Monitoring) project. These receivers are modified dual-frequency survey-grade NovAtel Euro4 receivers, with specialized firmware capable of deriving phase and amplitude scintillation information per minute from detrended 50 Hz observations. Observations also include raw GPS pseudorange and carrier phase observations, total electron content (TEC), 50 Hz phase (ADR) and amplitude observations, phase scintillation indices, and amplitude (S4) scintillation indices. Such data have been collected at three sites in western Canada over the past seven years. Sites are located at similar longitudes and in a range of latitudes spanning the sub-auroral region into the polar cap. Observations from these stations allow latitude profiling of the spatial extent of scintillation effects and investigation of auroral scintillation and polar scintillation effects. In this paper we exploit the CANGIM data set, augmented with other ground- and satellite-based instruments, to study the processes and characteristics of high-latitude scintillation effects. Scintillation events are identified and classified as auroral and polar. Phase and amplitude scintillation characteristics (magnitude, frequency, and spatial extent) are then investigated for each event, in order to gain insight into physical drivers and processes. Ground-based fluxgate magnetometer observations are obtained from CARISMA (Canadian Array for Real-time Investigations of Magnetic Activity) to determine the auroral/polar cap boundary through inferred latitude range of the auroral electrojets. COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission satellites are used to find co-located GPS radio occultation events, and derive vertical profiles of electron density to study the altitude distribution of irregularities. Interplanetary magnetic field (IMF) data are obtained from the Advance Composition Explorer (ACE) spacecraft to investigate the IMF orientation during scintillation events. This study includes twenty six events from the years 2003-2007. Analysis of scintillation events as a function of geomagnetic activity is also conducted. This study is intended to provide insight into the physical drivers of ionospheric scintillations, with application to physics-based simulation models used in development of more robust receiver designs – for modernized GPS or Galileo – in high latitude regions.
Author(s): Tiwari R, Ghafoori F, Fenek O-Al, Hadad O, Skone S
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: 23rd International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS)
Year of Conference: 2010
Pages: 349-360
Date deposited: 16/10/2013
Publisher: The Institute of Navigation
URL: http://www.ion.org/search/view_abstract.cfm?jp=p&idno=9162
