Use of maximum entropy spectral analysis to improve ship detection by over‐the‐horizon radar

Abstract

The over-the-horizon radar is able to detect ships over very large oceanic areas. Detection performance is sometimes reduced because of smearing of the sea echo due to variations of the Doppler shift imposed by the ionosphere. In this paper we propose a alecontamination procedure, based upon maximum entropy spectral analysis of sea scatter Bragg lines, to correct the phase of the signal before performing classical fast Fourier transform processing. The improvement in quality of the signal after phase correction results in a sharpening of spectral peaks. In the example presented the signal was chosen to contain spectral lines of a transponder installed on board a ship, to be used as reference lines. The decrease in the spectral width is significant for the sea scatter Bragg lines and for the transponder lines. As the Bragg lines sharpen, the ship echo is more easily detected in the spectrum. The proposed decontamination procedure involves more computation load than the simpler frequency shift method used for sea state monitoring, but, on the other hand, it can handle Doppler shift variations during coherent integration time.

Ionospheric decontamination for skywave OTH radar based on complex energy detector

“…From Equation (3), _ θ is the sum of 2πf b and linear scalar of the f(t). So, f(t) can be recovered using Equation (7). Once f(t) is demodulated, it can be used to compensate the phase shift caused by the ionosphere.…”

“…Several algorithms have been proposed. Bourdlillon et al [7] used maximum entropy spectral analysis algorithm to compensate the clutter. In this algorithm, one coherent processing interval (CPI) is divided into several short segments, during a short segment the Bragg frequency is regarded as stable.…”

Ionospheric decontamination based on sparse reconstruction for skywave radar

“…T ∈ C K 2 ×K 2 is a block diagonal matrix with K diagonal blocks, as formula (10). Each diagonal block matrix T i has the same size of…”

“…Bourdillon et al [10,11] proposed maximum entropy spectral analysis (MESA) to estimate contamination phase. But the method may fail in the case of fast phase fluctuation because fast phase fluctuation does not meet the method's assumption of linear phase in short period.…”

Study on detection and recognition of phase contamination and multimode propagation in ionosphere for OTHR

“…The popular correction methods of phase contamination include maximum entropy spectral analysis [1], phase gradient algorithm [2], frequencytime analysis [3], and so on. The correction methods of multimode propagation include the conversion from multimode to single-mode [4] and algorithm using circular operation of subtraction for sea clutter echo [5].…”