Geroski David J, Dzieciuch Matthew A, Dowling David R
Applied Physics Program, University of Michigan, Ann Arbor, Michigan 48109, USA.
Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, USA.
J Acoust Soc Am. 2021 Feb;149(2):853. doi: 10.1121/10.0003377.
Frequency-domain spatial-correlation analysis of recorded acoustic fields is typically limited to the bandwidth of the recordings. A previous study [Lipa, Worthmann, and Dowling (2018) J. Acoust. Soc. Am. 143(4), 2419-2427] suggests that limiting such analysis to in-band frequencies is not strictly necessary in a Lloyd's mirror environment. In particular, below-band field information can be retrieved from the frequency-difference autoproduct, a quadratic product of measured complex pressure-field amplitudes from two nearby frequencies. The frequency-difference autoproduct is a surrogate field that mimics a genuine acoustic field at the difference frequency. Here, spatial-correlation analysis is extended to deep-ocean acoustic fields measured during the PhilSea10 experiment. The frequency-difference autoproduct, at difference frequencies from 0.0625 to 15 Hz, is determined from hundreds of Philippine Sea recordings of 60 or 100 Hz bandwidth signals with center frequencies from 172.5 to 275 Hz broadcast to a vertical receiving array 129-450 km away. The measured autoproducts are cross correlated along the array with predicted acoustic fields and with predicted autoproduct fields at corresponding below-band frequencies. Stable measured cross correlations as high as 80%-90% are found at the low end of the investigated difference-frequency range, with consistent correlation loss due to mismatch at the higher below-band frequencies.
对记录的声场进行频域空间相关性分析通常限于记录的带宽。先前的一项研究[利帕、沃思曼和道林（2018年），《美国声学学会杂志》143(4)，2419 - 2427]表明，在劳埃德镜环境中，将这种分析限于带内频率并非严格必要。特别是，带外场信息可从频率差自乘积中获取，频率差自乘积是两个相邻频率处测量的复压力场振幅的二次乘积。频率差自乘积是一个替代场，它在差频处模拟真实的声场。在此，空间相关性分析扩展到了在PhilSea10实验期间测量的深海声场。频率差自乘积在0.0625至15赫兹的差频下，由数百个菲律宾海记录确定，这些记录是将中心频率从172.5至275赫兹的60或100赫兹带宽信号广播到129 - 450公里外的垂直接收阵列时得到的。测量得到的自乘积沿着阵列与预测的声场以及在相应带外频率处预测的自乘积场进行互相关。在研究的差频范围低端发现了高达80% - 90%的稳定测量互相关，在较高带外频率处由于失配导致了一致的相关损失。
