Abstract
Ionospheric clutter is one of the main problems for high-frequency surface wave radars (HFSWRs), as it severely interferes with sea surface state monitoring and target detection. Although a number of methods exist for ionospheric clutter suppression, most are suitable for radars with a large-sized array and are inefficient for small-aperture radars. In this study, we added an auxiliary crossed-loop antenna to the original compact radar antenna, and used an adaptive filter to suppress the ionospheric clutter. The experimental results of the HFSWRs data indicated that the suppression factor of the ionospheric clutter was up to 20 dB. Therefore, the Bragg peaks that were originally submerged by the ionospheric clutters could be recovered, and the gaps in the current maps can, to a large extent, be filled. For an oceanographic radar, the purpose of suppressing ionospheric clutter is to extract an accurate current speed; the radial current fields that were generated by our method showed an acceptable agreement with those generated by GlobCurrent data. This result supports the notion that the ionospheric suppression technique does not compromise the estimation of radial currents. The proposed method is particularly efficient for a compact HFSWRs, and can also be easily used in other types of antennas.
Highlights
Accepted: 20 October 2021High-frequency surface wave radars (HFSWRs) have been widely used in the remote sensing of sea surface dynamic parameters and vessels, owing to the ability of high-frequency (HF) radio waves to propagate along the sea surface, and to resonate with the scattering of sea waves and ships [1,2]
A number of high-frequency surface wave radars (HFSWRs), e.g., the SeaSonde [3], the Wellen Radar (WERA) [4], and the Ocean State Measuring and Analyzing Radar (OSMAR) [5], have achieved success in oceanographic applications; in practice there may be some energy transmitted in directions other than the desired horizontal direction, which is reflected by the ionosphere, and received by the radar
In order to improve the performance of ionospheric clutter suppression, we followed the clutter suppression method [16] with an auxiliary crossedsuppression, we followed the clutter suppression method [16] with an auxiliary crossedloop antenna for an OSMAR-S system, but simplified the structure of the adaptive filter loop antenna for an OSMAR-S system, but simplified the structure of the adaptive filter and adopted the recursive least squares (RLS) filtering algorithm instead
Summary
High-frequency surface wave radars (HFSWRs) have been widely used in the remote sensing of sea surface dynamic parameters and vessels, owing to the ability of high-frequency (HF) radio waves to propagate along the sea surface, and to resonate with the scattering of sea waves and ships [1,2]. Eng. 2021, 9, 1165 beamforming [11], space–time adaptive processing [12], and polarization filtering [13], lead to encouraging results, but their performances severely depend on the size of the lead toand encouraging results, but performances severely depend onsingle-channel the size of the array, array, are inefficient fortheir a compact radar. Ionospheric clutter suppression suppression is mainly aimed at the improvement of sea surface remote sensing [17]. In order to improve the performance of ionospheric clutter suppression, we followed the clutter suppression method [16] with an auxiliary crossedsuppression, we followed the clutter suppression method [16] with an auxiliary crossedloop antenna for an OSMAR-S system, but simplified the structure of the adaptive filter loop antenna for an OSMAR-S system, but simplified the structure of the adaptive filter and adopted the recursive least squares (RLS) filtering algorithm instead.
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