A Cascaded Approach for Correcting Ionospheric Contamination with Large Amplitude in HF Skywave Radars

Abstract

Ionospheric phase perturbation with large amplitude causes broadening sea clutter's Bragg peaks to overlap each other; the performance of traditional decontamination methods about filtering Bragg peak is poor, which greatly limits the detection performance of HF skywave radars. In view of the ionospheric phase perturbation with large amplitude, this paper proposes a cascaded approach based on improved S-method to correct the ionospheric phase contamination. This approach consists of two correction steps. At the first step, a time-frequency distribution method based on improved S-method is adopted and an optimal detection method is designed to obtain a coarse ionospheric modulation estimation from the time-frequency distribution. At the second correction step, based on the phase gradient algorithm (PGA) is exploited to eliminate the residual contamination. Finally, use the measured data to verify the effectiveness of the method. Simulation results show the time-frequency resolution of this method is high and is not affected by the interference of the cross term; ionospheric phase perturbation with large amplitude can be corrected in low signal-to-noise (SNR); such a cascade correction method has a good effect.

Deep Learning Aided Time–Frequency Analysis Filter Framework for Suppressing Ionosphere Clutter

“…Figure 5a shows the amplitude of STFT of the real target echoes, using the Hanning window with len = 160. Next, FSST is calculated by using (10), we can observe that the ridges of real targets are distinctly sharpened, showing as straight lines in the time-frequency plane. The representation information of targets concentrates on a few frequencies.…”

“…The operator defined in (10) is an approximation for the instantaneous frequency of the received signal at time t, filtered at frequency η. Then, the FSST coefficients are given by:…”

“…Furthermore, the joint transformation method is also suitable for the combination of STFT and other improved WVD methods [9]. As for skywave OTHR, Li et al firstly proposed an ionospheric phase contamination correction method based on an improved S-transform method and phase gradient algorithm (PGA) [10]. The S-transform is a time-frequency analysis technique proposed by Stockwell, Mansinha and Lowe [11].…”

Ionospheric phase decontamination based on sparse decomposition for multiple‐input multiple‐output over‐the‐horizon radar

“…Other specific parameters are shown in Table 2. A cosine function γ ( t ) = h cos(2 πf r t ) is used to simulate the actual ionospheric phase contamination [9, 11, 15, 17, 18], where h and f r are the amplitude and frequency of γ ( t ), respectively. The corresponding frequency modulation function of the ionospheric phase contamination is f γ ( t ) = − hf r sin(2 πf r t ).…”

“…There are also some ionospheric phase decontamination methods that are directly based on the original multi‐component radar echo instead of the calibration signal, e.g. MUSIC‐type method [10], Hankel rank reduction (HRR) method [12], and the improved time–frequency distribution method [17, 18]. These methods have the advantage of being independent of the calibration signal; this is helpful for coarse corrections of phase contamination, especially under severe broadening of Doppler spectrum.…”