A METHOD OF RECONSTRUCTING HORIZONTALLY-INHOMOGENEOUS IONOSPHERIC STRUCTURE USING HF SKY-WAVE BACKSCATTER IONOGRAMS

Abstract

High-frequency (HF) sky-wave backscatter sounding, as a powerful tool for detecting the ionosphere and studying the characteristics of radio channels, can be used to monitor the ionosphere continuously at a remote distance and to acquire the ionospheric parameters in a large area. Backscatter ionograms show the relationship between operating frequency, group path, and echo amplitude. Since an ionogram carries the information of the ionospheric profile along the detection path, the ionospheric parameters can be evaluated through the inversion technique. An algorithm for backscatter sounding ionogram inversion is developed based on the restriction of solution space to reconstruct the horizontally inhomogeneous structures of the ionosphere. Furthermore, the Newton-Kontorovich method that generally treats nonlinear operator equations and the Tikhonov regularization method that generally deals with ill-posed problems are effectively combined to resolve the equations. The algorithm can get a stable and unique solution under the solution space limitation. The algorithm we have developed was tested against both model data and observation data, and compared with the method of Fridman and Fridman (1994). Test results prove that the method in this paper has reliable convergence, is insensitive to measurement errors, and has higher accuracy for the inversion of ionospheric structures than the method of Fridman and Fridman (1994). Our algorithm not only can inverse horizontal changes in electron density under quiet conditions (at night or during the daytime at mid-latitudes), but also can diagnose the horizontally inhomogeneous structures of the ionosphere during sunrise or sunset periods with high accuracy. This consequently demonstrates the application value of the proposed algorithm in the treatment of the complex and volatile measured backscatter ionograms.