Horizontal Disc Random Array Performance. Hydrophone Arrays of Omnidirectional, Cardioid, and Iso-Opt Hypercardioid Elements Analyzed for Noise Gain and Directional Response in Vertically Directive Noise

摘要

Noise gains and directional responses are studied for horizontal disc random arrays with omnidirectional or directional hydrophones. The directional elements are pressure-gradient hydrophones of hypercardioid and cardioid limacon forms. Isotropic and vertically directive noise fields are considered along with a set of random arrays of the same relative shape. Since ocean noise below 200 Hz is due predominantly to shipping and above 200 Hz predominantly to wind, array sizes are studied that have design frequencies, fD, of 25 to 300 Hz and mean interelement spacings of one wavelength at each design frequency. Performance is analyzed from 10 to 600 Hz. Above the design frequency, the well-known gain of 10 log sub 10(N) is obtained with omnidirectional elements; but over much of the decade below the design frequency, the gain falls off and is linearly related to frequency. The gain improvement due to directional elements - as little as I dB and as much as 6 dB - is especially significant at frequencies below 0.1 fD and above fD. The directional responses considered include beam widths (directional resolution), sidelobe levels, and front-to-back response improvement due to directional elements. (Author)