Marine Physical Laboratory, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0238, USA.
Lynker Technologies, LLC, under contract to the Southwest Fisheries Science Center, NMFS/NOAA, La Jolla, California 92037, USA.
J Acoust Soc Am. 2019 Jul;146(1):95. doi: 10.1121/1.5114810.
The AN/SSQ-53 Directional Frequency Analysis and Recording (DIFAR) sonobuoy is an expendable device that can derive acoustic particle velocity along two orthogonal horizontal axes, along with acoustic pressure. This information enables computation of azimuths of low-frequency acoustic sources from a single compact sensor. The standard approach for estimating azimuth from these sensors is by conventional beamforming (i.e., adding weighted time series), but the resulting "cardioid" beampattern is imprecise, computationally expensive, and vulnerable to directional noise contamination for weak signals. Demonstrated here is an alternative multiplicative processing scheme that computes the "active intensity" of an acoustic signal to obtain the dominant directionality of a noise field as a function of time and frequency. This information is conveniently displayed as an "azigram," which is analogous to a spectrogram, but uses color to indicate azimuth instead of intensity. Data from several locations demonstrate this approach, which can be computed without demultiplexing the raw signal. Azigrams have been used to help diagnose sonobuoy issues, improve detectability, and estimate bearings of low signal-to-noise ratio signals. Azigrams may also enhance the detection and potential classification of signals embedded in directional noise fields.
AN/SSQ-53 定向频率分析和记录（DIFAR）声纳浮标是一种消耗性设备，可沿两个正交的水平轴以及声压来推导声粒子速度。这些信息可以从单个紧凑型传感器计算低频声源的方位。从这些传感器估计方位的标准方法是通过传统的波束形成（即，添加加权时间序列），但是得到的“心形”波束图案不准确，计算量大，并且容易受到弱信号的定向噪声污染。这里展示的是一种替代的乘法处理方案，该方案计算声信号的“主动强度”，以获得噪声场的主导方向性作为时间和频率的函数。此信息可以方便地显示为“方位图”，类似于声谱图，但使用颜色表示方位而不是强度。来自多个位置的数据证明了这种方法，无需对原始信号进行解复用即可进行计算。方位图已被用于帮助诊断声纳浮标问题，提高检测能力，并估计低信噪比信号的方位。方位图也可以增强定向噪声场中嵌入信号的检测和潜在分类。
