Last 30th June the PERSEUS  (Protection of European BoRders and Seas through the IntElligent Use of Surveillance) project came to an end. It has been developed according to theSeventh Framework Program, focusing on development and research in maritime security.
NATO CMRE, according to the Spanish INDRA society, developed and tested a new system for passive continuous underwater surveillance, which is able to elaborate acquired data and give results and alarms in real time.

The problem which has been solved is that conventional passive surveillance technologies can’t detect very fast boats, because they usually leave weak tracks, which cannot be recognized as if they don’t use AIS (Automatic Identification System)
To come through this problem, scientists and engineers introduced new technologies on mobile autonomous platforms, such as gliders, which are underwater robots, that can move changing their internal mass, and wave glider, which are particular gliders that use wave flow as energy source.

Acoustic monitoring system, used also for sea mammals detection, uses a very little passive antenna, which doesn’t send any signal, and a very sophisticated signal processing system.
Thanks to this new system, the recognition of different boat types is based on feature like spectral peaks, energy distribution and cavitation. System performances do not depend on local conditions where the system is working.
Available test results show that this new system can detect and track a small boat 900  m far from it, if the local noise doesn’t cover the signal too much.

The system error is about 10%, while medium azimuth error is about 5°. There are different kind of errors, such as underwater glider motion in dead reckoning mode, which means without satellite position, between two GPS positions (before and after immersion).

Preliminary experiments has been conducted in an harbor with high noise level and shallow waters. In such conditions, maximum positioning error was 5% and azimuth one about 2,5°. The same acoustic payload has been integrated in the Liquid Robotics wave glider . The system is based on a floating part and a submerged one.  Successful experiments in La Spezia in April 2015 and in Canaries Islands in May 2015.

Paolo Andrea Gemelli

16 July 2015