Research On Adaptive Elimation Methods Of Ionospheric Phase-path Disturlance

The OTHR utilize the high-frequency electromagnetic waves refraction by the ionosphere to achieve over the horizon detection. The characteristics of ion concentration and distribution in the ionosphere is variable and non-stationary, which made the phase of electromagnetic waves propagating in the ionosphere disturbed, and the echo spectrum spread or split, affecting the detection performance of the radar. Therefore, the ionosphere phase-path disturbance elimination method has been one of the key technologies of sky-wave radar signal processing.Firstly, this paper starts with the theory of ionospheric phase-path disturbance and theoretically analyze the influence on the echo data velocity dimensional spectrum when the ionospheic phase-path disturbing. Then the ionospheic phase-path disturbance dynamic model is built based on ionosphere real data. Analyzing the impact on ionospheric propagation path when the parameters of the dynamic model are changing. Comparing the differences between simulation results of velocity spectra and the actual echo spectrum, the basic disturbance model of ionospheric phase-path disturbance is obtained.Secondly, according to the size of the disturbance period, ionospheric disturbance can be divided into slow and fast phase-path disturbance, which produce different impact on echo spectrum structure. The spectrum structures of fast phase-path disturbance and multi-objective are similar while the mechanism are different. To achieve adaptive removal of ionospheric disturbances, criterions to distinguish slow phase-path and fast phase-path disturbance echo spectrum, as well as the fast phase-path disturbance and multi-objective are designed based on the difference between spectral peak and the differenct mechanism of production. These criterions can identify the echo spectrum automatically, which lay the foundation for adaptively processing ionospheric disturbances.Finally, the phase-path disturbance elimination algorithms are studied. In order to improve the accuracy of disturbance frequency estimation, this paper suggests an ionospheric disturbance removal algorithm based on short time MUSIC conversion. Then compared with common HRR_SVD, PWVD and PPS algorithms, the application conditions、differences of performance and algorithm efficiency are analyzed to compose the unity adaptive processing method. In addition,the experimental sky-wave radar data are used to verify the performance of the algorithms.