IEICE Electronics Express, Vol.7, No.6, 410–415 Ship ...

IEICE Electronics Express, Vol.7, No.6, 410–415

Ship detection and trackingusing multi-frequencyHFSWR

Xiaojing Huanga), Biyang Wen, and Fan DingSchool of Electronic Information, Wuhan University,

Luoyu Road, No. 128, Wuhan, 430079, China

a) andy h [email protected]

Abstract: Several field experiments were conducted to detect andtrack ships using a multi-frequency high-frequency surface-waveradar (HFSWR) system on the coast of East China Sea during 2009.Shipborne Automatic Identification System (AIS) was used to verifythe results. And the algorithm of detection and tracking was provedto be efficient and practical.Keywords: target, detection, tracking, HFSWR, multi-frequencyClassification: Electron devices, circuits, and systems

References

[1] D. Barrick, “History, present status, and future directions of HF surface-wave radars in the U.S.,” Proc. Int. Radar Conf., pp. 652–655, 2003.

[2] A. M. Ponsford, L. Sevgi, and H. C. Chan, “An Integrated MaritimeSurveillance System Based on High-Frequency Surface-Wave Radars Part2 Operational Status and System Performance,” IEEE Antennas Propag.Mag., vol. 43, no. 5, pp. 52–63, 2001.

[3] S. Liu, H. Hagiwara, R. Shoji, H. Tamara, and T. Okano, “Radar networksystem to observe & analyze Tokyo Bay vessel traffic,” IEEE Aerosp.Electron. Syst. Mag., vol. 19, no. 11, pp. 3–11, 2004.

[4] B. Y. Wen, Z. Y. Lei, F. Cheng, and Z. G. Ma, “Preliminary researchon target detection in first-order peaks with adaptive cancellation,” 3rdInt. Conf. Comput. Electromagn. Appl., Beijing, PEOPLES R CHINA,pp. 512–515, Nov. 2004.

[5] G. Wang, X.-G. Xia, B. T. Root, and V. C. Chen, “Moving target detec-tion in over-the-horizon radar using adaptive chirplet transform,” Proc.IEEE Radar Conf., pp. 77–84, 2002.

[6] B. T. Root, “HF radar ship detection through clutter cancellation,” Proc.IEEE Radar Conf., RADARCON 98, Dallas, TX, USA, pp. 281–286, May1998.

[7] V. Fabbro, P. F. Combes, and N. Guillet, “Apparent radar cross sectionof a large target illuminated by a surface wave above the sea,” ProgressIn Electromagnetics Research, PIER, vol. 50, pp. 41–60, 2005.

[8] D. E. Barrick, B. J. Lipa, P. M. Lilleboe, and I. Mountain, “Gated FMCWDF radar and signal processing for range/doppler/angle determination,”U.S. patent, Application Number:5361072, 1994.

[9] G. Fabrizio, A. Farina, and A. D. Maio, “Knowledge-based adaptive pro-cessing for ship detection in OTH Radar,” Int. Radar Symposium, IRS2006, pp. 1–5, May 2006.

c© IEICE 2010DOI: 10.1587/elex.7.410Received December 29, 2009Accepted February 22, 2010Published March 25, 2010

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[10] H. Song, K. Heng-yu, and W. Bi-yang, “Multiple target tracking dataprocessing for HF Grand Wave Radar,” J. Wuhan University (NaturalScience Edition), vol. 49, no. 3, pp. 391–395, 2003.

1 Introduction

In recent years, possibility of Over-The-Horizon (OTH) visibility in HFSWRsystems has attracted more and more attention. Now, more researchersare shifting focus from ocean environment monitoring to ship detection [1].Though many novel techniques have been reported on that field, few provideverified results [2], because it’s lack of the information of targets. The con-ventional method to get the information is employing a cooperative target.But its shortcomings are obvious: It’s inefficient and not able to reflect thecomplex actual situation.

A monostatic multi-frequency HFSWR system for both ocean monitoringand ship detection has been developed by Wuhan University in the past years.We tested the radar system in the past months, and compared the radar datawith the AIS [3] information.

At HF band, the difficulty in target detection arises from the strongocean clutter, which can submerge ships in Doppler domain and lead to blindspeed. For wide beam HF Radar with a small antenna array, the broadenedfirst order peaks complicate that effect further, and few effective detectionalgorithms in first-order peaks have been put forward yet [4], though manytime-frequency [5] and clutter-cancellation [6] techniques were reported to beapplied on narrow beam case or on the target near the peaks. Multi-bandHF radar can effectively solve this problem, because the speed of the wavesthat cause the Bragg effect changes with the radiated frequency.

Another advantage of operation on multi-frequency is that it providesmore robust ship tracks than single frequency HF radars outside the blindarea. This tracking robustness is achieved by avoiding target fading due toecho nulls from frequency and azimuthal variations in ship radar-cross-section(RCS) that occur using a single radar frequency [7].

2 Radar system

The radar system covers 7.5∼25 MHz HF band, which include 4 sub-bands:7.5∼10 MHz, 10∼13 MHz, 13∼18 MHz and 18∼25 MHz. It’s able to work at4 frequencies at most through time-division-multiplexing (TDM). A spec-trum monitor is used in the system to help to select the best frequencies.Frequency modulation interrupted continuous wave (FMICW) is adopted asrange resolving technique. The sweep bandwidth is able to change, so therange resolution is variable from 1 km to 5 km. The pulse-repetition-interval(PRI) is little less than 0.4 s and variable. A waveform-design module cal-culates and sets all the variable parameters when we change the system’swork status. We design the max detection range 150 km when the average


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transmitted power is 300 W. However, the transmitted power is set muchlower than the design value in our field experiments.

A wideband array composed of 3 monopole elements is designed for trans-mission. The receiver array 20 m away is composed of 8 monopole elementsplaced in π shape with another monopole element beside connected to thespectrum monitor. All the antennas are located in a 100 m × 50 m field. Thevery-high-frequency antenna for AIS receiver is mounted on the roof of theoperator’s house 50 m away from the field. The antennas are illustrated inFig. 1.

Fig. 1. Antenna field

3 Signal processing

The processing chain is shown in Fig. 2. For every single frequency, a doublefast-Fourier-transform (FFT) process [8] is used to produce a Range-Doppler(RD) power spectrum map in every 512 PRI which we call a snapshot. ARD map (512 Doppler cells × 80 range cells) illustrates the Doppler spectrafrom all range gates as shown in Fig. 3. A calibration algorithm follows it tomatch the 8 channels with the assistance of AIS information. Then, digital-beam-forming (DBF) is processed to get a set of RD maps for azimuths from−60◦ to 60◦ at a step of 2◦ in a snapshot, and to obtain a data cube: 61beams × 512 Doppler-cells × N range-cells. Here, N is also variable, and atypical value is 80. We prepare those Rang-Doppler-Azimuth (RDA) datacubes for the detection process that follows the DBF in the processing chain.

For target detection under the conditions of single frequency, constantfalse-alarm-rate (CFAR) detection is the technology we focus on. Past expe-rience demonstrates that target detection processing in RDA domain is thebest option for our radar. We have developed a three step detection tech-nique based on CFAR. First of all, peak detection is performed to a RDAcube to find all the 3-demension peaks that may be caused by a hard targetin a snapshot. To discard the noise peaks and avoid false alarms, CFAR tests


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Fig. 2. Signal processing chain

Fig. 3. RD map (a) for a channel (b) for a target’s DOA

are performed both in range dimension and Doppler dimension successivelyin the consequent steps. The peaks above the adaptive threshold are takenas echo from ships except for some islands with a zero-Doppler frequency andsea clutter peaks in the Bragg area. After filtering those clutters [9], we getthe target cells in the RDA cube.

An estimator then works on each target cell to obtain the ship’s profilesincluding azimuth, range and radial velocity. We apply Akaike’s informationcriterion (AIC) to test whether the echo have a single direction of arrival(DOA). Then, multiple-signal-classification (MUSIC) algorithm is appliedto estimate the DOA with an accuracy better than 1◦ with a moderate signalto noise radio (SNR). And the result is taken as true only when it is in thesector of the target obtained by the former DBF. Another DBF is done atthe DOA to obtain the RD map for that direction as shown in Fig.3 (b) inwhich the examined target is enhanced and the targets at other directions are


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weakened. The range and radial velocity are estimated from that RD map.Though the range resolution is low in the HF radar system, an accuracy ofbetter than one tenth of the resolution can be achieved with a moderate SNRby range interposition.

All the steps mentioned above are under the single frequency conditions.Finally, all the targets’ information is merged together to obtain a set oftargets’ information under multi-frequency conditions. Targets detected atdifferent frequencies are taken as one if they are close enough in the profile

Fig. 4. Output of tracks from radar and AIS


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space. At last, the sequence of the estimation results is associated to formtracks by a tracker based on joint probabilistic data association (JPDA)algorithm [10].

4 Result

An example of our tracking result is shown in Fig. 4 (a) that records thesituation at 0:40 on August 26, 2009. The fine lines are tracks from ourradar system’s output, and the wide are ship location information from theAIS. The outputs from the two systems match well. Though multi-frequencyis used, the AIS provides much information. But the radar can cover a widerrange as shown in Fig. 4 (b) recorded at 2:00 on August 31, 2009, even if thetransmitter power is limited.

5 Conclusion

We developed a multi-band HF radar system for ship detection and trackingwith AIS as assistant information system. The results of our processingmatch the AIS information well.

Acknowledgments

This work is supported by the National Scientific Fund Committee (NSFC)under grant 6067103 and the Eleventh-Five-Year 863 High-Tech Project ofChina under grant 2007AA09Z101. The authors wish to express their grati-tude to the editor and the anonymous reviewers.


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