With suitable test equipment, it is possible to determine the acoustic signature of a ship such as a submarine in port. Based on a measurement, the software generates a color map, which highlights the points of strong acoustic emission, also called “hot spots”. Thus, the main sources having a direct impact on the discretion of the vessel can be located, quantified, characterized and identified. Easily and quickly determining an acoustic signature in the hold can be a key step before a more expensive validation at sea. Such an operation is typically of great interest after a maintenance intervention in order to see if this has had an impact on this signature.
The methodology used is that of near-field acoustic holography (NAH - Nearfield Acoustic Holography ). The first step is the acquisition of sound pressure underwater and near the hull. Considering the typical shape of submarines, a cylindrical NAH method is essential. For this, a cylindrical antenna made up of about twenty hydrophones is positioned near the hull to measure the underwater acoustic pressure. The propulsion system is started but decoupled. In addition, all the machines likely to emit noise are put into operation. During this operation the antenna is moved to different positions along the hull over the entire area to be mapped. The signals emitted by the hydrophones are acquired by the OROS instruments and analyzed by the dedicated software: OROS Underwater Holography. The maps are back-propagated onto the hull by calculation and broadcast to the outside in order to estimate the noise radiated in the far field of the ship. Finally, these maps are determined frequency by frequency. OROS's underwater holography solution is the only one currently available on the market.