Background:

One of the most challenging aspects of port security is providing protection from that approach from beneath the surface of water as well as from above the surface of water. Explosive device delivery can occur as explosive can be delivered underwater and can be carried to shore by people using underwater breathing apparatus such as SCUBA gear.

Current hydro-acoustic detection systems may use either active or passive SONAR Active SONAR can be misleading since plenty of false alarms are triggered due to fish, marine mammals and shallow bottoms. Also, there are high possibilities of system being detected by intruder as well as they might be harmful for marine mammals. Some passive systems need to be large and heavy, consisting of relay of hundreds of sensors in order to work efficiently. Also, once deployed, passive SONARs are permanent. They can cover large areas, known as priori, but may fail for smaller areas such as harbors, backwaters, etc.

Summary:

The focused system relates to a portable, easily deployable and recoverable multi-transducer hydro-acoustic detection system that can detect the presence and location of sources of hydro-acoustic emissions produced by an intruder such as diver, swimmer, UUV etc. this system uses passive acoustics where sound energy is only detected and not emitted.

The system uses four acoustic sensors such as under-water hydrophones , in very small area cluster. The whole system can include at least three such clusters. The system can achieve results comparable to the techniques consisting hundreds of sensors in a given area of interest. Also, array of sensors is not required by this system to cover large priori.

Preliminary analysis of the acoustic characterization of potential targets such as divers with SCUBA gear, unmanned under-water vehicles (UUVs), diver propulsion vehicles (DPVs) has been performed on the system using empirically, gathered data, acoustic signal analysis. And analytic modelling through various experiments. The systems has portrayed effectiveness in urban estuarine environment where adequate modelling is not much possible. It can also seperate various targets on basis of bearing angle between sensors and targets.  This patent can also utilize high accuracy Sensor Position system  to determine precise position of each hydrophone in their cluster. This helps in accurate and rapid deployment of system in marine environment. The SPS system may also measure sensor sensitivity for changes over time that will occur due to movement of sensors due, e.g. to currents, or embedding in the water bottom, or fouling by marine substances or underwater life forms.

The patent meets US navy’s Integrated Swimmer Detection Program Requirements. The patent system is easily portable, deployable and recoverable. It can be redeployed within one hour. It is very light weight with weight measuring in tens of pounds. With multi-cluster arrangements it can provide a 360-degree detection.

Benefits:

- Passive system

- 360 degree scanning possible in a cluster arrangement

Applications:

- Secret surveillance

- Intruder detection without intruder(s) knowledge

Full Patent: Passive Underwater Acoustic System For Detection Localization And Classification Of Acoustic Sources

Image Source: https://www.semanticscholar.org/paper/Stevens-Passive-Acoustic-System-for-underwater-Sutin-Bunin/99ff47e50fb98561dbac3d2732d94ff8e8ad8c68/figure/4