Correction of Ionospheric Distortion on HF Hybrid Sky‐Surface Wave Radar Calibrated by Direct Wave

Abstract

The performance of the high-frequency hybrid sky-surface wave radar is often degraded due to the distortion of radar echoes induced by time-varying ionosphere. Here a modified S-transform method based on the direct wave for ionosphere decontamination of high-frequency hybrid sky-surface wave radar is presented. First, we extract the time-varying-ionosphere-distorted phase of the echoes from the direct wave of high-frequency hybrid sky-surface wave radar by using the modified S-transform. Then this phase function is used to decontaminate the ionosphere distortion of radar echo at each range bins. Simulations and experimental data are conducted to validate the performance of the proposed method on decontaminating the distortion. The experimental data are acquired by Wuhan Universitys ocean state measuring and analyzing radar. A mass of radar data is processed and analyzed, demonstrating that the decontamination effect is statistically significant. The method is not only effective to remove the Doppler shift of direct wave and Bragg peaks caused by ionosphere but also able to narrow the broadened direct wave and Bragg peaks. Meanwhile, the SNR is improved in most range bins; the background noise is reduced detectably, sometimes significantly; and some isolated radar echoes near direct wave or Bragg peaks are recovered or enhanced. These results indicate that the proposed decontamination algorithm works well.

Azimuth Resolution Improvement and Target Parameters Inversion for Distributed Shipborne High Frequency Hybrid Sky-Surface Wave Radar

“…Under the assumption of a quiet ionosphere, the ionosphere only causes the variation of the group-range, which ignores its effect on the phase of echo signals. However, the phase of the echo signals under non-stationary ionospheric conditions will be affected by a phase modulation and random perturbations [3,[41][42][43][44][45], so perturbation correction methods [5,57] are needed to improve the performance of algorithms. Moreover, ionospheric parameters vary during the day, year, and solar cycle, which affects variations in signal propagation in the ionosphere.…”

“…The shipborne HFHSSWR not only maintains the capacity of long range over the horizon target detection and wide-area coverage of the HF sky-wave radar, but also retains the stability and long integration time of the HF surface wave radar (HFSWR). It also has the advantage of maneuverability of the shipborne HFSWR, which has an advancement in wide-area surveillance of over-the-horizon targets and ocean environment [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. However, the shipborne HFHSSWR suffers from low azimuth resolution and poor estimation accuracy in azimuth, due to the small array aperture limited by the confined space on a shipborne platform.…”

Correction of ionosphere phase contamination of high‐frequency hybrid sky‐surface wave radar using wavelet transform

“…We adopt the direct wave extraction method proposed in Ref. [9], but we improve the method for identifying the direct wave boundary. By analysing the measured data used in this paper, the range of 0.07 Hz on both sides of the peak is more suitable for the boundary of the direct wave.…”

The Suggested Reciprocal Relationship between Maximum, Minimum and Optimum Usable Frequency Parameters Over Iraqi Zone

“…It's also called surface wave, sometimes called line-of-sight wave (LOS), VHF signals (and signals at higher frequencies) propagate in straight lines directly from one antenna to another, and sky waves frequently known as the ionospheric waves, are radiated in a skyward direction and refunded to Earth at some distant place due to refraction from the layer of ionosphere. This method of propagation is comparatively unaffected by the Earth's surface and might propagate signals over long distances (10).…”