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Spencer, P. S. J.
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Spencer, P. S. J.
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- PublicationRestrictedImaging of the Antarctic ionosphere: Experimental results(2009-11)
; ; ; ; ; ; ; ; ; ; ; ;Yin, P.; College of Electronic Information Engineering,Civil Aviation University of China,Tianjin,China ;Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, Bath BA2 7AY,UK ;Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Pinnock, M.; British Antarctic Survey, UK ;Spencer, P.; Department of Electronic and Electrical Engineering, University of Bath, Bath BA2 7AY, UK ;De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Newell, P.; Johns Hopkins University, Applied Physics Laboratory, USA ;Sarti, P.; Istituto Radio Astronomia (IRA)-INAF, Bologna, Italy ;Negusini, M.; Istituto Radio Astronomia (IRA)-INAF, Bologna, Italy ;Capra, A.; Università di Modena e Reggio Emilia, Italy; ; ; ; ; ; ; ; ; ; Ground-based dual-frequency GPS observations can be used to create images of electron density.This is well established for the Arctic ionosphere; here one of the first results is presented for the Antarctic. In this study, the GPS receivers in the Antarctic are supplemented with another GPS receiver onboard CHAMP. The aim of the study is to demonstrate the technique for investigating geophysical events, for example, an ionospheric disturbance period on 11 February 2004. The images have been validated by in-situ measurements from DMSP and CHAMP satellites, as well as Super Dual Auroral Radar Network (SuperDARN) convection patterns, which are able to confirm the location, presence, and transportation of large-scale plasma patches. This study indicates that although the convection still dominates in the high-latitude ionosphere, soft precipitation within the polar cap may play a role in the evolution of the polar patches. It also illustrates the potential for future multi-instrument studies of the Antarctic.304 34 - PublicationRestrictedDynamics of high-latitude pathches and associated small-scale irregularities during the October and November 2003 storms(2008)
; ; ; ; ; ; ; ; ;De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Aquino, M.; IESSG, The University of Nottingham, University Park, Nottingham NG7 2RD, UK ;Dodson, A.; IESSG, The University of Nottingham, University Park, Nottingham NG7 2RD, UK ;Mitchell, C. N.; Electronic and Electrical Engineering, University of Bath, Bath, UK ;Spencer, P.; Electronic and Electrical Engineering, University of Bath, Bath, UK ;Wernik, A. W.; Space Research Center, Polish Academy of Sciences, Warsaw, Poland; ; ; ; ; ; ; Observations from a network of specially equipped GPS scintillation receivers in Northern Europe are used to investigate the dynamics of ionospheric plasma during the storm events of 30 October and 20 November 2003. The total electron content (TEC) and scintillation data, combined with ionospheric tomography produced by the multi-instrument data analysis system (MIDAS), reveal strong enhancements and steep gradients in TEC during nighttime under a prevailing negative Bz component of the interplanetary magnetic field (IMF). Amplitude and phase scintillation maxima are often co-located with the TEC gradients at the edge of plasma patches, revealing the presence of small-scale irregularities and suggesting association with a tongue of ionization (TOI) convecting in an anti-sunward direction from the American sector across the polar cap. Similarities and differences between the ionospheric response to the two storms are investigated. The 30 October event reveals a quite complex scenario showing two phases of plasma dynamics: the former reflects the expected convection pattern for IMF Bz southward and the latter possibly indicates a sort of TEC plasma stagnation signature of the more complex convection patterns during several positive/negative excursions of IMF Bz.392 34 - PublicationOpen AccessTotal electron content - A key parameterin propagation: measurement and usein ionospheric imaging(2004)
; ; ; ; ; ; ; ; ; ; ;Kersley, L.; University of Wales, Aberystwyth, U.K. ;Malan, D.; University of Wales, Aberystwyth, U.K. ;Pryse, S. E.; University of Wales, Aberystwyth, U.K. ;Cander, L. R.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K. ;Bamford, R. A.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K. ;Belehaki, A.; National Observatory, Institute for Space Applications and Remote Sensing, P. Penteli, Athens, Greece ;Leitinger, R.; Institute of Physics, Institute for Geophysics, Astrophysics and Meteorology (IGAM), University of Graz, Austria ;Radicella, S. M.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Aeronomy and Radiopropagation Laboratory, Trieste, Italy ;Mitchell, C. N.; University of Bath, U.K. ;Spencer, P. S. J.; University of Bath, U.K.; ; ; ; ; ; ; ; ; The paper reports on a series of studies carried out within the COST 271 Action relating to the measurement and use of Total Electron Content (TEC) of the ionosphere over North West Europe. Total electron content is a very important parameter for the correction of propagation effects on applied radio systems so that it is vital to have confidence in the experimental measurements and the resultant products derived as aids for the practical user. Comparative investigations have been carried out using TEC values from several different sources. It was found that in general there was broad statistical agreement between the data sets within the known limitations of the techniques, though discrepancies were identified linked to steep ionospheric gradients at the onset of geomagnetic storm disturbance and in the vicinity of the main trough. The paper also reviews recent progress in the development of tomographic inversion techniques that use total electron content measurements to image the ionosphere as an aid to various radio systems applications.298 2206 - PublicationOpen AccessImaging of fast moving electron-density structures in the polar cap(2007-06)
; ; ;Spencer, P. S. J.; Department of Electronic and Electrical Engineering, University of Bath, U.K. ;Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, U.K.; The imaging of fast-moving electron-density structures in the polar cap presents a unique set of challenges that are not encountered in other ionospheric imaging problems. GPS observations of total electron content in the polar cap are sparse compared to other regions in the Northern Hemisphere. Furthermore, the slow relative motion of the satellites across the sky complicates the problem since the velocity of the plasma can be large in comparison and traditional approaches could result in image blurring. This paper presents a Kalman-filter based method that incorporates a forward projection of the solution based on a model plasma drift velocity field. This is the first time that the plasma motion, rather than just integrations of electron density, has been used in an ionospheric imaging algorithm. The motion is derived from the Weimer model of the electric field. It is shown that this novel approach to the implementation of a Kalman filter provides a detailed view of the polar cap ionosphere under severe storm conditions. A case study is given for the October 2003 Halloween storm where verification is provided by incoherent scatter radars.226 763 - PublicationOpen AccessA three-dimensional time-dependent algorithm for ionospheric imaging using GPS(2003)
; ; ;Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, U.K. ;Spencer, P. S. J.; Department of Electronic and Electrical Engineering, University of Bath, U.K.; Global Positioning System (GPS) satellite receivers provide a world-wide network of phase and group delay measurements. The combination of two-frequency measurements can be used to derive the integral of the electron concentration along each satellite-to-receiver path, a parameter known as the Total Electron Content (TEC). At this stage these slant TEC data are diffi cult to interpret as they originate from a combination of a temporally changing ionosphere and spatially changing observation geometry. In this paper TEC data are inverted to evaluate the underlying distribution and time evolution of electron concentration. Accordingly, a new three-dimensional, time-dependent algorithm is presented here for imaging ionospheric electron concentration using GPS signals. The inversion results in a three-dimensional movie rather than a static image of the electron-concentration distribution. The technique is demonstrated using simulated ground-based GPS data from actual measurement geometry over Europe.388 794