Passive acoustic underwater intruder detection system

An intruder detection apparatus comprising:

• a plurality of acoustic emission sensors arranged in a cluster, the cluster forming a polygon defining at least two axes of alignment between respective pairs of acoustic emission sensors within the cluster;
• a computing device in cooperation with a non-transitory computer readable storage medium comprising computer readable instructions for performing via the computing device a method comprising:
• receiving a first signal produced by a first acoustic emission sensor within a respective pair of acoustic emission sensors, in response to the first acoustic emission sensor detecting an acoustic emission from a source, and receiving a second signal produced by a second acoustic emission sensor within the respective pair of acoustic emission sensors, in response to the second acoustic emission sensor detecting the acoustic emission from the source;
• determining a cross-correlation factor between the first signal and the second signal;
• and,
• determining a bearing to the source based on the cross correlation factor;
• the plurality of acoustic emission sensors each comprising a hydrophone,
• the hydrophones forming the cluster are tethered to each other through a center pod;
• the center pod comprising:
• a buoyancy mechanism;
• and,
• a bottom mooring mechanism;
• and,
• a mechanism for releasing the center pod from the bottom mooring mechanism, whereby the center pod and the hydrophones are recoverable at a surface of a body of water on the bottom of which the center pod and hydrophones had been deployed.

A method for intruder detection comprising:

• receiving, via a computing device, a first signal produced by one acoustic emission sensor within a first pair of acoustic emission sensors, in a cluster of a plurality of acoustic emission sensors, arranged beneath the surface of a body of water, the cluster defining the first pair and a second pair of acoustic emission sensors, the first signal being produced in response to said one acoustic emission sensor detecting a first acoustic emission generated by and emanating from a source, and receiving, via the computing device, a second signal produced by another acoustic emission sensor within the first pair, the second signal being produced in response to said another acoustic emission sensor detecting the first acoustic emission generated by and emanating from the source and receiving, via the computing device, at least a third signal produced by one acoustic emission sensor within the second pair in the cluster, the third signal being produced in response to said one acoustic emission sensor within the second pair detecting a second acoustic emission generated by and emanating from the source;
• determining, via a computing device, a first cross-correlation factor between the first signal and the second signal, based on a time difference between the detection of the first acoustic emission by the acoustic emission detectors of the first pair;
• determining, via a computing device, a second cross-correlation factor relating to at least the third signal and another signal from another acoustic emission sensor of the second pair, based on a time difference between the detection of the second acoustic emission by the acoustic emission sensors of the second pair;
• determining, via a computing device, a bearing to the source based on at least one of the first cross correlation factor and the second cross correlation factor;
• and
• determining, via a computing device, a range to the source based on at least one of the first correlation factor and the second correlation factor.

A non-transitory computer readable storage medium storing instructions for execution by a computing device to perform an intruder detection method, the method comprising:

• receiving a first signal produced by one acoustic emission sensor within a first pair of acoustic emission sensors, in a cluster of a plurality of acoustic emission sensors, arranged beneath the surface of a body of water, the cluster defining the first pair and a second pair of acoustic emission sensors, the first signal being produced in response to said one acoustic emission sensor detecting a first acoustic emission generated by and emanating from a source, receiving a second signal produced by another acoustic emission sensor within the first pair, the second signal being produced in response to said another acoustic emission sensor detecting the first acoustic emission generated by and emanating from the source, and receiving at least a third signal produced by one acoustic emission sensor within the second pair, the third signal being produced in response to said one acoustic emission sensor within the second pair detecting a second acoustic emission generated by and emanating from the source;
• determining a first cross-correlation factor between the first signal and the second signal based on a time difference between the detection of the first acoustic emission by the acoustic emission detectors of the first pair;
• determining a second cross-correlation factor relating to at least the third signal and another signal from another acoustic emission sensor of the second pair, based on a time difference between the detection of the second acoustic emission by the acoustic emission sensors of the second pair;
• determining a bearing to the source based on at least one of the first cross-correlation factor and the second cross-correlation factor;
• and
• determining a range to the source based on at least one of the first cross-correlation factor and the second cross-correlation factor.