2010 年 37 巻 1 号 p. 34-45
For underwater port surveillance, it is important to develop a technique that can automatically detect slow-moving targets such as divers. It is difficult to detect such targets since their echoes are masked by undesirable signals such as random noises, reverberations, wake bubbles, echoes of static objects, and crosstalk noises generated by multibeam processing. To detect moving targets effectively, a signal processing method that can eliminate only these undesirable signals is required. However, conventional methods that deal with only signal amplitude cannot remove these undesirable signals easily since random temporal fluctuations of amplitudes are incorrectly identified as moving targets, leading to many false detections. We propose a new signal detection method that uses an interferometric technique that can effectively eliminate only the undesirable signals, and detect moving targets. The proposed method deals with temporal fluctuations of phase difference measured by the split-beam method independently from amplitude-based methods. The spatiotemporal fluctuation of phase difference is closely related to the movement of a target, and it is possible to detect moving targets effectively by evaluating the spatiotemporal variance of the phase difference. In this study, the authors developed an algorithm for the proposed target detection method. By applying the proposed method to experimental data, we have confirmed that it has high detection performance compared to conventional methods.