Naval Submarine Medical Research Laboratory

Operating in a dangerously sensor-limited closed environment, submarine sonar operators are plagued by primitive sensory interfaces inherited from earlier hardware designs. The inefficient match to the operator’s perceptual capability is exacerbated as submarines increasingly operate in the littoral where, at now reduced ranges from quieter threat targets, detection requires immediate action for crew safety. Present use of the sonar operator’s auditory ability ignores the superior acuity of the mammalian binaural system. In humans, this system is sensitive to minute instantaneous differences in phase, intensity and time of arrival between its two channels. This research developed, and perceptually tested, a binaural auditory display that optimized the essential noise correlation between a pair of formed listening beams. To generate the necessary perceptual characteristics for the binaural display, a breakthrough audio beamforming process formed beams from a hull mounted wide-aperture hydrophone array (WAA) which were focused at two different distances but in the same direction. This unique processing, named Spatial Vernier Beamforming (SVBF), maintained the essential high noise correlation between the pair of formed directional beams. Once appropriate beamforming was proven feasible, laboratory testing was undertaken to quantify perceptual performance. A representative sample of 15 sonar contacts were beamform processed, stored as wavefiles and systematically presented to a group of 18 highly experienced sonar operators. Results show a highly significant 8.6 dB detection improvement over the current single beam display. This improvement represents the ability to acoustically detect targets at more than twice the distance currently achieved. This signal processing technology provides an advanced auditory display which allows immediate interaural comparisons of pairs of focused beams. This broader coverage binaural real-time display is particularly well suited in littoral warfare. Performance gains such as: 1) simultaneous vs. serial comparison of beams of different distance, for more rapid detection of acoustic changes (including transients), 2) increased real-time information on target distance, 3) reduced operator uncertainty and increased alerting cues from target motion 'across the head' during sequential ranging, will significantly enhance crew safety in modern close-in operations. It can be linked to photonics mast display. The SVBF dual beam data are ideal for adaptive real-time signal processing, since the noise common to the two beams can be mathematically removed to expose the target. As a result SVBF processes are amenable to real-time digital signal extraction for presentation in 3-D audio displays which are ideal for situational awareness.