Application of computerized tomography to the investigation of ionospheric structures

Abstract

Ionospheric total electron content (TEC) measurements, obtained simultaneously at several locations, can be processed using computerized tomography (CT) algorithms to obtain two-dimensional images of ionospheric electron density. Using TEC data, computerized ionospheric tomography (CIT) reconstructs an image of the electron density structures in a vertical slice above the receiving stations. We successfully applied this technique to realistic simulations of ionospheric density variations over 16 ø of latitude and a height range of 50 to 1000 km. A method for approximating the peak height and scale height of the electron density profile will be discussed as well as a reconstruction technique based on the multiplicative algebraic reconstruction technique algorithm and a back projection based initial guess. The quality of reconstructions is considered for two geometries and image resolutions. In particular, the image of a mid-latitude trough with background horizontal density gradient and large-scale irregular structures has been reconstructed from TEC data generated from a model based on an incoherent scatter radar observation. The CT reconstructed image was compared with the original contour map obtained by the incoherent scatter radar. Good agreement has been achieved. The CIT technique has also been applied to a modeled ionosphere to calculate the range rate corrections for a Doppler-tracking radar. INTRODUCTIONRecently, Austen et al. [1988] have demonstrated the feasibility of using a computer tomography (CT) technique for imaging ionospheric electron density. The CT technique involves using one-dimensional information to reconstruct a two-dimensional image. The data consist of measurements of the line integral of electron density in the ionosphere for many different paths. The line integral paths can be considered as many unique rays traversing the plane of the image. The image region can be gridded into small areas or pixels, and within each pixel the parameter will assume some constant value. What is desired is the distribution of the parameter over the image. In the case of the ionosphere the integrated parameter is electron density. The line integral of electron density over some path is the total electron content (TEC). Using a chain of stations receiving the beacon signal from an orbiting satellite, a geometry can be created such that the TEC measurements can be used to reconstruct a vertical slice image, or vertical cross section, of ionospheric electron density in a vertical plane between the satellite and the ground stations.The feasibility of using CT for imaging ionospheric electron density has been shown by Austen et al. [1988] by applying the technique to successfully reconstruct iononspheric structures from synthetic TEC data generated from computer models. In this paper we will discuss the results from a further test of the technique. From a mapping of the mid-latitude ionospheric trough obtained by the Chatanika radar [Weber et al., 1985] the Air Force Geophysics Laboratory (AFGL) group (J. A...

Application of tomographic inversion in studying airglow in the mesopause region

“…Austen et al, 1988;Raymund et al, 1990;Andreeva et al, 1992). In this sort of approach one starts from some initial distribution and continues the iteration until the stop criterion is met.…”

“…Satellite radio tomography for measuring the ionospheric electron density was suggested by Austen et al, (1986), and it has later been developed in a great number of papers (e.g. Austen et al, 1988;Raymund et al, 1990;Andreeva et al, 1992;Fremouw et al, 1992;Kunitsyn and Tereshchenko, 1992;Pryse and Kersley, 1992;Pryse et al, 1993;Markkanen et al, 1995;Nygre n et al, 1996b). The method has now reached a level which allows its use in ionospheric research (Mitchell et al, 1997).…”

Ionospheric Tomography by Neural Network Collocation Method

“…Since Austen et al, [4] applied the algebraic reconstruction technique (ART) to the twodimensional analysis of model TEC data generated by a computer simulation various methods for CIT were proposed and applied to analyses of model data and real observation data. Though the two-dimensional ionospheric tomography has been studied extensively from both the theoretical and observational aspects [5][6][7], in these studies only the ionospheric structure within a cross-section defined by the satellite orbit and the ground receiver array can be obtained, which limits strongly the observation time and place. In order to cope with the problem methods for author's e-mail: takeda-t@gakushikai.jp the three-dimensional CIT are being studied intensively by many authors [8][9][10][11][12][13][14].…”

Optimal truncation criterion for application of singular value decomposition to ionospheric tomography

“…These beacons are observed by a series of ground receivers positioned approximately in a line of latitude. In ionospheric electron-density reconstruction, three difficulties need to be overcome [Raymund, 1995]. generic notations, we focus on how to evaluate our solution, how to determine the boundary between information and noise, and how to construct the generalized inverse matrix and the corresponding solution with the aid of singular value decomposition (SVD).…”