Study On Ionospheric Clutter Detection And Assessment Of Pollution Level

With abilities to anti-stealth, super-horizon detection and work around the clock, high frequency ground wave radar (HFSWR) has been widely used in the low-altitude, surface target detection and monitoring of the marine environment. HFSWR is seriously affected by the ionosphere clutter. Ionospheric clutter can raise the floor of power spectrum and destroy the detection background, which cause huge difficulty for target detection. In order to minimize the impact of ionospheric clutter, on the one hand, suppressing it after it is detected On the other hand, assessing of the impact of ionospheric clutter under different operating frequencies, then choosing the best for the radar.To achieve the above purpose, this article focuses on the method of detecting ionospheric clutter, and studies the method of pollution assessment for ionospheric clutter. The research of this paper mainly includes the following aspects:Firstly, the typical signal environment for HFSWR is analyzed deeply, and we mainly focus on the features of sea clutter and ionospheric clutter. Sea clutter and ionospheric clutter is the two most important ingredients in the radar signal, this paper illustrates the inducement mechanism of the first and second order sea clutter, and discusses their role in target detection and sea state monitoring. The inducement, path and propagation characteristics of ionospheric clutter are also introduced.Then, the method of detecting the spread ionospheric clutter on range-Doppler profile (RDP) is introduced, and the actual radar data proved its effectiveness. The detection process is divided into three steps. First the first-order sea clutter is identified and eliminated in order to eliminate its influence. Then the RDP is segmented by a threshold, a binary image is obtained, which retains spatial information of strong elements. Finally binary image is processed, recognition results of ionospheric clutter is obtained. Applying these methods to the actual RDP, the detection and identification result is satisfactory.Finally, the method of assessment ionospheric clutter's pollution level is studied. Based on ionospheric clutter's detection and identification results, the density of the clutter, the average power of the clutter are defined, which can describe the clutter's influence. Method of assessment of ionospheric clutter's pollution level based on single factor or multiple factors is considered respectively. In addition, the method of fuzzy synthetic evaluation on clutter pollution level is discussed. The actual clutter data is assessed by the above methods, and the result is listed. Furthermore, the choice of operating frequency based on the ionospheric clutter's pollution level in HFSWR is illustrated.