Multistatic Acoustic Source for Unmanned Underwater Vehicles

A review of acoustic propagation in Shallow-Water (SW) shows thatactive sonar detection ranges are generally limited byreverberation caused by backscatter from the surface, biologicalpopulation, and the bottom. The effects are exacerbated in theVery-Shallow-Water (VSW) and Surf Zone (SF) due to air-bubblesfrom breaking waves and sediment stirred-up by wave action.These unsavory acoustic conditions makes the detection andlocation of mines and obstacles in the VSW/SZ of potentialamphibious landings a virtual impossibility by conventional sonarsystems. However, all of these factors are greatly reduced byoperating at lower-frequencies while, at the same time, retainingthe narrower beam patterns associated with higher-frequencies.Parametric operation of active sonars is a well establishedtechnology for obtaining lower frequencies with relatively narrowbeam patterns, but in a manageable size. Phase I propagationmodel studies of such a system yielded mine detection ranges of~3,500 yards in the VSW/SZ. For Phase II a GFE projector,identified as PADS-II projector, will be modified andrefurbished. Corner-reflector hydorphones will be fabricated forreceiving both the primary frequency band and the parametricfrequency bands. After calibration, the projector-receiversystem will be utilized for exploratory studies of parametric andprimary frequency detection of experimental mine-like targets inthe very shallow waters, but limited ranges, of Dodge Pond.These preliminary measurements will yield