Limitations of ionospheric imaging by tomography

Yeh, K. C.; Raymund, T. D.

doi:10.1029/91rs01873

Cited by 104 publications

(53 citation statements)

References 14 publications

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“…Radio tomography has also been used to image the latitudinal structure of the trough. The method in this case suffers from limited ray-path geometry set by the configuration of the satellites and receivers (Yeh and Raymund, 1991) and requires a priori information to support the reconstruction process (Raymund et al, 1993). In another inversion application Mitchell and Spencer (2003) presented an algorithm using GPS observations that yielded the timeevolving, three-dimensional ionospheric electron concentration.…”

Section: Introductionmentioning

confidence: 99%

Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

et al. 2018

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Abstract. The main ionospheric trough is a large-scale spatial depletion in the electron density distribution at the interface between the high-and mid-latitude ionosphere. In western Europe it appears in early evening, progresses equatorward during the night, and retreats rapidly poleward at dawn. It exhibits substantial day-to-day variability and under conditions of increased geomagnetic activity it moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the trough minimum, and their variability, can cause problems for radio applications. Numerous studies have sought to characterize and quantify the trough behaviour.The Electron Density Assimilative Model (EDAM) models the ionosphere on a global scale. It assimilates observations into a background ionosphere, the International Reference Ionosphere 2007 (IRI2007), to provide a full 3-D representation of the ionospheric plasma distribution at specified times and days. This current investigation studied the capability of EDAM to model the ionosphere in the region of the main trough. Total electron content (TEC) measurements from 46 GPS stations in western Europe from September to December 2002 were assimilated into EDAM to provide a model of the ionosphere in the trough region. Vertical electron content profiles through the model revealed the trough and the detail of its structure. Statistical results are presented of the latitude of the trough minimum, TEC at the minimum and of other defined parameters that characterize the trough structure. The results are compared with previous observations made with the Navy Ionospheric Monitoring System (NIMS), and reveal the potential of EDAM to model the large-scale structure of the ionosphere.

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Section: Introductionmentioning

confidence: 99%

Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

et al. 2018

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“…The relative merits of different methods to obtain TEC for CIT have been discussed by Yeh and Raymund [1991], and the importance of geometry was stressed by several authors, including Brown and Ganguly [2001]. The typical observational geometry for group delay or differential phase TEC measurement is not favorable to the estimation of the vertical structure of the ionosphere, including the height of the F 2 peak.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric reconstruction using Faraday rotation data: A new technique

Ganguly¹,

Brown²,

Dasgupta³

et al. 2001

Radio Science

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Abstract. Measurements of total electron content of the ionosphere by recording group delay or differential phase of transionospheric satellite signals have been used for reconstruction of ionospheric profiles. Integrated electron content measurements contain little information of ionospheric height distribution and require precise observations. These measurements are difficult for VHF and higher frequencies and require reasonably sophisticated instruments. Faraday rotation measurements, on the other hand, require relatively simple instruments and were widely used throughout the world. Faraday rotation of HF, VHF, and lower UHF band signals contains an additional term, e.g., a known function of the magnetic field. The functional form depends on the ray path and orientation of the magnetic field and in general is a complex quantity. Since the magnetic field distribution in the Earth's ionosphere is known with very high precision, this information can be used to obtain improved reconstruction of the ionospheric profiles. The magnetic field components have a strong dependence with the height, and this provides additional information regarding the ionospheric height retrieval. We have performed simulations using these techniques, and we present results using both simulated data as well as Faraday rotation data measured from several stations. We compare the sensitivities and reconstruction of ionospheric profiles using group delay and Faraday rotation techniques and demonstrate the improvements with the use of Faraday rotation data. The most difficult (in terms of radio propagation) regions, i.e., those near the equatorial regions, are simulated, and data from several stations, i.e., those near Calcutta, India, as well as those from several stations in Africa, are used. For the first time, we present the results of the reconstruction of the ionosphere using both simulated and observed Faraday rotation data. Large amounts of Faraday rotation data have been acquired during the 1960s and 1970s. These data contain a history of the ionosphere. The present technique would allow retrieval of ionospheric profiles over extended regions and could allow inferences to be drawn regarding the long-term changes in the ionosphere. The technique can also be incorporated in future satellite beacons, and the combination of group delay and Faraday rotation techniques will allow us to obtain superior reconstructions. IntroductionTotal electron content (TEC) has been measured since the earliest days of artificial satellites. Propagation of radio waves in the ionospheric plasma leads to advancement in carrier phase and produces group delay for modulation. Both of these quantities are related directly to the integrated column densities and have been used to measure the integrated elec-

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“…There are substantial differences between medical and ionospheric scenarios mainly due to the geometry of the problem. CIT has, in fact, limitations such as limited angle observations and uneven/sparse distribution of the ground stations [4,5] that make the solution unstable and difficult to solve. However, the capability of the method was demonstrated by Mitchell et al [6] where, along a quasi-2D plane, features in the electron density were revealed at mid and auroral latitudes.…”

Section: Introductionmentioning

confidence: 99%