SiPLABoratory

Underwater Acoustic Barriers for harbour protection (UAB)

UAB (project POCI/MAR/59008/2004) aims at studying, develop and test in the field the concept of an underwater acoustic barrier for detecting intruders in a given area, that can be an harbour, bay, or strait. This project is financed under the POCI programme of FCT with 72 keuros for 2 years. Starting date: January 1st, 2006.

The present project proposal aims at studying, develop and test in the field an underwater acoustic barrier (UAB). The objective of an UAB is to detect underwater intrusions in a given area of the ocean, like for instance, a bay, a port or a river. One of the most promising concepts in this area today is to form a virtual plane between two vertical acoustic transmitting/receiving line arrays of transducers/receivers, the sea surface and the bottom, using the acoustic time-reversal mirror (TRM) principle. The two vertical line arrays (VLA) are connected either by cable or by a wireless lan. Forming a focused TRM on each of the receivers of the VLA will allow, in principle, the detection of any acoustic reflecting object perturbing the acoustic field when crossing the barrier. There are two type of problems to be treated in this project: theoretical problems dealing with the optimal frequency and number and distribution of sensors of the VLA's allowing a adequate resolution of the targets and technological problems dealing with the assembling of the system formed by the two synchronized VLA's being able to work on real time and in shallow waters (20/30 m).

The objectives of the UAB project can be summarized as follows:

• to study the feasibility of establishing an underwater acoustic virtual barrier being able to detect submerged targets down to the size of a scuba diver, in order to protect sensitive shallow water areas like bays, harbors and river mouths. The system will be based on the one-way time-reversal mirror (TRM) concept, using two arrays: one on each side of the passage to be protected.
• to develop and test at sea the projected system in a shallow water area (say 10 to 30 m deep) along the Portuguese coast. The system will be composed of two short vertical arrays, one active and one passive, located 200 to 500 m apart and connected by wireless LAN or by cable.
• to conclude on the required steps to make the proposed system a pre-comercial operational system.