GPS‐based ionospheric tomography is a well‐known technique for imaging the total electron content (TEC) between GPS satellites and receivers. However, as an integral measurement of electron concentration, TEC typically encompasses both the ionosphere and plasmasphere, masking signatures from the topside ionosphere‐plasmasphere due to the dominant ionosphere. Imaging these regions requires a technique that isolates TEC in the topside ionosphere‐plasmasphere. Multi‐Instrument Data Analysis System (MIDAS) employs tomography to image the electron distribution in the ionosphere. Its implementation for regions beyond is yet to be seen due to the different dynamics present above the ionosphere. This paper discusses the extension of MIDAS to image these altitudes using GPS phase‐based TEC measurements and follows the work by Spencer and Mitchell (2011). Plasma is constrained to dipole field lines described by Euler potentials, resulting in a distribution symmetrical about the geomagnetic equator. A simulation of an empirical plasmaspheric model by Gallagher et al. (1988) is used to verify the technique by comparing reconstructions of the simulation with the empirical model. The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) is used as GPS receiver locations. The verification is followed by a validation of the modified MIDAS algorithm, where the regions' TEC is reconstructed from COSMIC GPS phase measurements and qualitatively compared with previous studies using Jason‐1 and COSMIC data. Results show that MIDAS can successfully image features/trends of the topside ionosphere‐plasmasphere observed in other studies, with deviations in absolute TEC attributed to differences in data set properties and the resolution of the images.

Ionospheric scintillation is the rapid fluctuation of both phase and amplitude of trans-ionospheric radio waves due to small scale electron density irregularities in the ionosphere. Prediction of the occurrence of scintillation at L band frequencies is needed to mitigate the disruption of space-based communication and navigation systems. The purpose of this paper is to present a method of using tomographic inversions of the ionospheric electron density obtained from ground-based GPS data to infer the location and strength of the post-sunset plasma drift vortex. This vortex is related to the pre-reversal enhancement in the eastwards electric field which has been correlated to the subsequent occurrence of scintillation.

This paper outlines a new mathematical approach to imaging the electron density distribution in the high regions of the topside ionosphere and the plasmasphere from 800 km up to 20,200 km altitude using GPS measurements from low Earth orbit (LEO) satellites. The problem of ionospheric imaging using ground‐based GPS measurements has been studied for a number of years. Such methods have proved extremely useful in providing details of the larger‐scale morphology of the global ionosphere. The work presented extends these methods to image the plasmasphere up to altitudes of the GPS satellites at 20,000 km. The problem of limited observations due to the small number of LEOs in operation is overcome by constraining the plasmaspheric electron density to be constant along magnetic field lines. A coordinate transform from a spherical coordinate system to one defined in terms of Euler potentials is sufficient to provide unambiguous solutions. Preliminary results using data from the COSMIC satellite constellation are presented showing the response of the plasmasphere to changes in the interplanetary medium.

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.

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.

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.

Fast and reliable ambiguity resolution (AR) is particularly challenging in long-range real-time kinematic (RTK) global positioning system (GPS), since the atmospheric errors decorrelate with the increasing base-rover separation, effectively reducing the success rate of integer fixing. In order to improve the speed and the success rate of AR, external atmospheric corrections are required. In this paper, four different methods of ionosphere modeling are used as a source of external information, and their impact on the speed and reliability of AR and the rover positioning accuracy is discussed. An example data set, collected by the Ohio Continuously Operating Reference Stations on August 31, 2003, is analyzed, with special emphasis on varying ionospheric conditions during the course of the day in order to study the applicability of these ionospheric models to high-accuracy RTK GPS. In particular, the time-to-fix, the level of AR success, and the accuracy of the resulting rover coordinates are analyzed. Each method displays a different level of accuracy, and thus varying applicability to support AR under changing, ionospheric conditions.

() University of Wales, Aberystwyth, U.K. () Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K. () National Observatory, Institute for Space Applications and Remote Sensing, P. Penteli, Athens, Greece () Institute of Physics, Institute for Geophysics, Astrophysics and Meteorology (IGAM), University of Graz, Austria () The Abdus Salam International Centre for Theoretical Physics (ICTP), Aeronomy and Radiopropagation Laboratory, Trieste, Italy () University of Bath, U.K.

Dual frequency receivers of the global navigation satellite system (GNSS) of the recently established South African Network of more than 40 geodetic grade GPS base station receivers provide a valuable tool by means of which the ionospheric conditions over Southern Africa can be determined with a better time and spatial resolution than is currently possible using only the available three ionosonde sites. Electron density profiles obtained by tomographic reconstruction of GPS derived total electron content measurements, as augmented with ionosonde measurements has the potential to become a tool to quantify ionospheric variability and investigate ionospheric dynamics and medium- and smaller-scale ionospheric structures such as travelling ionospheric disturbances. The local network of dual frequency GPS reference stations have been deployed by various agencies in South Africa to provide correction data for geodetic and surveying applications. This paper presents the first results of ionospheric tomography using data from the Trignet network of GPS stations in South Africa. The tomographic imaging is done by means of the MIDAS program. Verification is provided through comparison with electron density profiles derived from the three South African ionosonde sites.

A new method has been devised for two, three and four-dimensional inversion of satellite and ground-based measurements taken from diverse instrumentation. The time-dependent algorithm is applied to multi-directional ground-based GPS data. The output of the inversion is a three-dimensional movie of electron concentration. This technique is demonstrated by showing a series of images of the ionosphere during the storm of July 2000, from the auroral to the northern equatorial regions. The images reveal the large-scale dynamics of the ionosphere during disturbed conditions and show the great potential of GPS data for such geophysical studies.

A simulation-based comparison between two approaches to Total Electron Content (TEC) mapping is presented. The first method is the thin-shell model, and the second is a full inversion through a 3-D volume. The advantage of the inversion approach is demonstrated quantitatively. In particular, we examine the effect on the calculation of slant TEC from two locations in Europe using the two different approaches to TEC mapping. We also demonstrate the effect of the horizontal grid size on the results.

Ionospheric imaging is now well established with over 20 years of research having proven the techniques for both scientific studies and radio system planning tools. Many algorithms now use data from the Global Positioning System (GPS). GPS has revolutionised our ability to monitor the entire ionosphere simultaneously on a global scale. However, the vertical resolution of the images and in particular the separation of the topside ionosphere with the plasmasphere remains a challenge. A further issue is the uneven coverage of ground-based receivers across the Earth. After a general introduction to the science, this paper focuses on two issues; first is the determination of the vertical profile in ionospheric imaging and the ionosphere/plasmasphere separation. A new approach to the determination of the basis functions is discussed that takes into account the plasma behaviour along the magnetic field. Secondly the sparsity of data over certain regions of the Earth and the challenges of producing images with a consistent and reliable resolution standard is considered. Future improvements in both of these areas and the science expected with new low-Earth orbit satellites are discussed.