Research On Ionosphere Decontamination And Altitude Estimation Algorithm For Skywave Over-the-horizon Radar

Ionospheric decontamination and target’s altitude estimation have a very important significance in skywave over-the-horizon radar(OTHR). Skywave radar transmits high-frequency wave into the air to detect the target and the wave will be reflected by the ionosphere. The instability of ionosphere will contaminate the echo’s phase. The Doppler spectrum of echo will be broadened, making it more difficult to detect the targets. Therefore, it is necessary to compensate the echo to improve the detecting performance of skywave radar. In addition, target’s altitude is a very important information. People can obtain the target’s type, manage flight path, and detect enemy’s secret base according to the altitude. At present, estimation accuracy of some existing decontamination algorithms is not high enough and some algorithms may fail in the case of fast phase fluctuation. The current altitude estimation algorithms of skywave radar are not ideal. The estimation accuracy is not high enough and the convergence speed is not fast enough.This paper makes a deep study about these problems, summarized as follows:(1) Research on the matched Fourier transform algorithm to compensate phase contaminationProposes an algorithm to compensate phase contamination based on the matched Fourier transform. Firstly, uses the three-order phase function to approximate echo piecewisely. Then estimates the contamination function based on matched Fourier transform algorithm to achieve decontamination function. Simulation results show that the proposed algorithm is better than the traditional Hankel Rank Reduction(HRR) algorithm and needn’t the priori information of echo component. Furthermore, the proposed algorithm achieves better decontamination performance under the situation of both fast and slow phase fluctuation.(2) Research on the high precision algorithm based on sparse reconstruction to compensate phase contaminationBased on the above matched Fourier transform decontamination algorithm, proposes a phase decontamination algorithm with high precision based on sparse reconstruction. Firstly, transforms the problem of estimating ionospheric contamination phase into a sparse optimization problem, then solve it rapidly by the split Bregman iterative method to achieve decontamination function. Simulation results show that the proposed algorithm has a higher estimation precision and better decontamination performance than the complex energy detector(CED) algorithm. Furthermore, the proposed algorithm works well under the situation of both slow and fast phase fluctuation or in the case of both high and low clutter to noise ratio.(3) Research on altitude estimation based on ionospheric joining layer model and maximum likelihood matched field algorithmPresents a matched field maximum likelihood altitude estimation algorithm based on ionospheric joining layer model. Firstly, constructs the ionosphere model with joining layer and a likelihood function about target’s altitude. Then, solve the maximum value of the joint probability density to achieve target’s altitude. Simulation results show that the algorithm achieves a faster convergence speed and a higher estimation accuracy.