Improving Ship Detection in Clutter-Edge and Multi-Target Scenarios for High-Frequency Radar

Zhiqing Yang,Hao Zhou,Yingwei Tian,Wei Shen,Weimin Huang

doi:10.3390/rs13214305

Abstract

As one of the main sensors for continuous maritime measurements of sea state parameters, high-frequency surface wave radar (HFSWR) also plays an important role in ship detection and tracking. Compact HFSWR often suffers from missing targets, especially when the target appears near the Doppler region with heavy sea clutter or near another target in a multi-target scenario. To address this problem, an automatic ship detection method based on time–frequency (TF) analysis is presented in this paper. The TF target ridge areas are extracted in the TF image via the eigenvalues of the Hessian matrix, image edge detection, and local maximum search. Then, whether ship signals exist in the TF ridges or not is decided by a decision threshold that is calculated by fitting the probability distribution function (PDF) of sea clutter in the TF domain. The proposed TF method can separate TF ridges of similar Doppler frequency and performs constant false alarm rate (CFAR) detection for TF targets, which facilitates detecting these targets that are masked by sea clutter and other large targets. Experimental results show that the number of detected ships that match with the automatic identification system (AIS) records is four times more than that obtained by the conventional constant false alarm rate (CFAR) detectors and 1.3 times more than that by the state-of-the-art TF method in consideration of approximately the same number of detected targets.

Highlights

High-frequency surface wave radar (HFSWR) has the advantages of long detection range, real-time, and continuous operation in all weathers compared with microwave radar [1,2], and has been used in most coastal countries for sustained observations of the ocean surface
Data as reference, the results from a three-day long experiment show that the total number of matched targets detected by TF-constant false alarm rate (CFAR) is 7304, much more than the 1487 detected by the other five conventional CFAR methods
time–frequency constant false alarm rate (TF-CFAR) obtains matched targets 4.91 times more those obtained by conventional CFAR for the case of targets at the edges of the

Summary

Introduction

High-frequency surface wave radar (HFSWR) has the advantages of long detection range, real-time, and continuous operation in all weathers compared with microwave radar [1,2], and has been used in most coastal countries for sustained observations of the ocean surface. It should be noted that the maximum radar detection range depends on its frequency, bandwidth, and power. With a typical bandwidth of 100 kHz, an operating frequency of 8 MHz, and 30 watts of transmitting power, the WEllen RAdar (WERA) achieves ship detection ranges up to 200 km [9]. With a frequency of 4.55 MHz, a bandwidth of 25 kHz, and an average radiated power of 40 watts, a long-range SeaSonde high-frequency radar can “see” ships to a range of approximately 120 km [10].

Methods

Results

Discussion

Conclusion