| The HFSWR is a large and powerful electronic device with the huge transmitting and receiving arrays,which adds the function of simultaneous detection of the ocean and ionosphere to the existing target detection function.In other words,the new multifunctional multi-mode system of target-ocean-ionosphere detection can not only detect targets at sea,but also obtain ocean-ionosphere information simultaneously,providing two-dimensional ocean-ionosphere information for the study of the dynamics between the ocean and ionosphere.This is an important direction for the development and application of the new HFSWR system and a major frontier scientific research topic.In particular,sea state remote sensing(mainly currents,wind speed and wave fields)is an important area of research in HFSWR and has been widely developed and applied.In contrast,research on HFSWR ionospheric echoes(including the cancellation algorithm)has lagged far behind that on sea state remote sensing(including the cancellation algorithm),and the complex ionospheric echo(clutter)problem is still a key technical problem for HFSWR engineering applications that has not yet been fully solved.In addition to the complexity of the ionospheric echo itself,there is a lack of basic research on the characteristics of the HFSWR echo.Therefore,the study of ionospheric echo dynamics from the perspective of system dynamics is an important way to deeply understand the ionospheric echo characteristics in essence.This paper focuses on the research needs of the new multifunctional multi-mode system HFSWR with integrated target-ocean-ionosphere detection,and the ionospheric echo signal as the main research object,and also focuses on the research of the ionospheric echo disturbance and chaotic dynamics characteristics of HFSWR to provide a new theoretical and technical approach to the research of the dynamics relationship between the ocean and the ionosphere.The main research elements of this paper are as follows.(1)The ionosphere and ionospheric echo characteristics.The physical characteristics of the ionosphere,including the electrical properties of the ionosphere,the dispersion of electromagnetic waves in the ionosphere,the equation of motion of the plasma in the ionosphere,and the stratification of electron concentration,are first briefly discussed,followed by a detailed analysis of the basic characteristics of the ionospheric echoes in the distance,Doppler,time and space domains in HFSWR,laying the foundation for the subsequent study of the ionospheric echo dynamics.(2)Improved algorithm for automatic acquisition of deep learning from HFSWR ionospheric echoes.In order to meet the real-time requirements of HFSWR ionospheric echo dynamics characteristics,automatic acquisition of ionospheric echoes from complex HFSWR echo signals is required.To address the problems that traditional image processing methods rely on manual experience to design acquisition criteria in advance and the low accuracy of edge acquisition to meet the real-time requirements of HFSWR ionospheric echo dynamics characteristics,a deep learning algorithm is introduced to achieve automatic acquisition of HFSWR ionospheric echoes.A multi-labeled data set including ionospheric echoes is created using the RD spectral map of HFSWR echoes during typhoons,and the performance of existing deep learning algorithms for acquiring HFSWR ionospheric echoes is evaluated.To address the shortcomings of the existing deep learning algorithms in the automatic acquisition performance of HFSWR ionospheric echoes,an improved deep learning algorithm for automatic acquisition of HFSWR ionospheric echoes is proposed and the performance is evaluated with the measured HFSWR data.The results show that the improved algorithm fullfills the real-time requirement for the study of the dynamics of HFSWR ionospheric echoes.(3)Gravity wave-ionospheric perturbation characteristics of HFSWR.The gravity wave is carrier of energy and kinetic energy transporting between the ocean and the ionosphere and plays a very important role in the ocean-ionosphere dynamics relationship.Generally speaking,gravity waves excited by sudden sea states(e.g.typhoons,tsunamis,thunderstorms,etc.)travel through complex propagation paths to reach the ionosphere,triggering fluctuations in ionospheric electron concentrations and eventually manifesting themselves as Travelling Ionospheric Disturbances(TIDs).The ability of HFSWR to obtain information on the TIDs and thus to observe the gravity waves that trigger them which has the characteristics of the ionospheric dynamics studied in this paper.It is important to note that the gravity waves studied in this paper refer to atmospheric gravity waves excited by sudden sea states and propagating to ionospheric heights that can trigger ionospheric disturbances.To this end,the Doppler shift model of the HFSWR ionospheric echoes is derived based on the ionospheric disturbance mechanism and the atmospheric gravity wave background of the tilted ionosphere.The Doppler frequency shift model is validated and the ionospheric disturbance characteristics are analyzed using the measured data during the typhoon Rumbia and Fireworks,thus demonstrating the capability of HFSWR to observe gravity waves and to improve the understanding of sudden sea state induced ionospheric disturbances.This will improve the understanding of the response mechanism of ionospheric disturbances excited by sudden sea states and provide a theoretical basis for HFSWR to explore the ocean-ionosphere dynamics.(4)Chaotic characteristics of ionospheric echoes from HFSWR.Based on the analysis of Haykin’s criterion and Zero-One method,the joint chaos test criterion for HFSWR ionospheric echo signals is proposed to relax the limitation that Haykin’s test criterion,which is only applicable to smooth signals,and to compensate for the inability of Zero-One method to distinguish weak chaos from periodic signals by phase space reconstruction and three-dimensional spatial attractor embedding.The problem of detecting chaos in HFSWR ionospheric echoes,which are non-stationary,high time-varying and multi-scale complex signals with multiple paths modulated and coupled to each other,is better solved by the phase space reconstruction and three-dimensional spatial attractor embedding.The chaotic characteristics of the HFSWR ionospheric echoes are found to have chaotic dynamics by examining the joint criteria for the chaotic characteristics of the measured HFSWR ionospheric dataset,and the chaotic characteristics of the ionospheric echoes during non-typhoon periods are analyzed.The relationship between the chaotic characteristic parameters of the echoes and the detection distance unit(heights)is analyzed.Finally,a comparison of the chaotic parameters of the HFSWR ionospheric echoes during typhoon and non-typhoon periods shows that the variation of the chaotic parameters is influenced by the quasi-periodic fluctuations of the gravity waves.The variation pattern of the chaotic parameters will provide a new theoretical basis and technical approach for the early warning monitoring and prediction of the sudden sea state.This research will contribute to the scientific study of the dynamics of the oceanionosphere complex large system of HFSWR,and thus to the research and realization of a new multifunctional multi-modal HFSWR system with integrated target-ocean-ionosphere detection,as well as provide new technical approach for the early warning monitoring and prediction system of the sudden sea state and the study of the HFSWR ionospheric echo(clutter)countermeasures. |
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