Bonnel Julien, Thode Aaron M, Blackwell Susanna B, Kim Katherine, Macrander A Michael
Lab-STICC, ENSTA Bretagne (Université Européenne de Bretagne) 2 rue François Verny, 29806 Brest Cedex 9, France.
Marine Physical Laboratory, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0238.
J Acoust Soc Am. 2014 Jul;136(1):145-55. doi: 10.1121/1.4883358.
Bowhead whales generate low-frequency calls in shallow-water Arctic environments, whose dispersive propagation characteristics are well modeled by normal mode theory. As each mode propagates with a different group speed, a call's range can be inferred by the relative time-frequency dispersion of the modal arrivals. Traditionally, at close ranges modal arrivals are separated using synchronized hydrophone arrays. Here a nonlinear signal processing method called "warping" is used to filter the modes on just a single hydrophone. The filtering works even at relatively short source ranges, where distinct modal arrivals are not separable in a conventional spectrogram. However, this warping technique is limited to signals with monotonically increasing or decreasing frequency modulations, a relatively common situation for bowhead calls. Once modal arrivals have been separated, the source range can be estimated using conventional modal dispersion techniques, with the original source signal structure being recovered as a by-product. Twelve bowhead whale vocalizations recorded near Kaktovik (Alaska) in 2010, with signal-to-noise ratios between 6 and 23 dB, are analyzed, and the resulting single-receiver range estimates are consistent with those obtained independently via triangulation from widely-distributed vector sensor arrays. Geoacoustic inversions for each call are necessary in order to obtain the correct ranges.
北极露脊鲸在北极浅水环境中发出低频叫声，其传播特性可用简正波理论很好地建模。由于每个简正波以不同的群速度传播，叫声的传播距离可通过简正波到达的相对时频色散来推断。传统上，在近距离时，使用同步水听器阵列来分离简正波到达信号。这里使用一种称为“扭曲”的非线性信号处理方法，仅在单个水听器上对简正波进行滤波。即使在相对较短的声源距离处，这种滤波方法也有效，在传统频谱图中不同的简正波到达信号是不可分离的。然而，这种扭曲技术仅限于频率调制单调增加或减少的信号，这在北极露脊鲸叫声中是比较常见的情况。一旦简正波到达信号被分离，就可以使用传统的简正波色散技术估计声源距离，原始声源信号结构作为副产品被恢复。分析了2010年在阿拉斯加卡克托维克附近记录的12次北极露脊鲸发声，信噪比在6至23分贝之间，得到的单接收器距离估计与通过广泛分布的矢量传感器阵列三角测量独立获得的结果一致。为了获得正确的距离，每次叫声的地声反演是必要的。
