Pacific Noise and Vibration - Ship Noise Monitoring and Acoustic Vulnerability Systems

When making a tactical decision, it is of paramount importance that a naval command element has ready access to all possible information regarding a vessel’s performance. One of the most important factors to consider is a ship’s stealth-at-sea – how much noise the vessel is making, and how susceptible it is to enemy detection. Australia-based experts in acoustic technology, PNV, develop and supply a range of systems that can accurately measure and report a vessel’s acoustic presence, allowing commanders to make important decisions.

STEALTH-AT-SEA SYSTEMS

PNV’s stealth-at-sea systems monitor every aspect of a vessel’s acoustic presence, from engine signature to incidental noise caused by onboard crew activity. A vessel’s presence in relation to environmental noises such as weather conditions and marine life are also taken into account, allowing for an accurate and comprehensive assessment of a vessel’s stealth at sea capabilities.

SHIP NOISE MONITORING SYSTEMS

All vessels underway produce broadband and discrete narrowband noise that is a combination of hydrodynamic noise and noise generated by the ship’s crew and the operation of onboard equipment machinery. The installation and utilisation of a Ship Noise Monitoring System (SNMS) is a fundamental requirement through which to address applied stealth-at-sea, and hence to assess platform vulnerability on a near-real-time basis.

An SNMS serves to provide command with a means to monitor and store its own acoustic signature using an online data storage system, compare the current readings with class and hull averages, localise the source of abnormal radiated noise, and adjust the ship’s operating mode accordingly; and employ other shipborne hull-mounted and deployable sensors in order to monitor the ship’s radiated acoustic signature.

The PNV SNMS consists of any combination of permanent and / or handheld sensors for the monitoring of onboard machinery, coupled with on-board databases containing radiated noise data obtained from Nearfield Acoustic Holography (NAH) or Dynamic Range measurements, and augmented by other at-sea signature measurement techniques such from sonobuoys or a towed array.

The consolidation and update of these data sources, and the manipulation of the data to account for the prevailing environmental conditions will allow the on-line assessment of vulnerability to a variety of threats, and hence the ability to tailor the machinery state and radiated noise posture for the operational situation.

COMMAND ACCOUSTIC VULNERABILITY SYSTEMS

Vulnerability is a relative measure, a comparison of the capabilities of own-vessel sensors and systems, and the threat, with both affected and modified by what lies between them, namely the environment.

The PNV Command Acoustic Vulnerability System (CAVS) is designed as a tactical decision aid for commanders and warfare staff of ships and submarines. CAVS can take input from stored data (such as from a noise ranging or NAH measurement) or from the dynamic data from an appropriate ship noise monitoring system, and combine this with stored threat information to generate a vulnerability assessment for a variety of operational threats.

The vulnerability assessment software provides the following functions:

• Analysis, display and provision of alarms regarding own-noise signature, relation of these alarms to particular sensors
• Determination and display of automatic updates from the operational state and SNIC clues of the own sonar noise induced performance alterations
• Calculation of acoustic propagation in the vessel’s environment, display of ray trace patterns and the subsequent determination of acoustic zones of interest relevant to the ship’s location (convergence zones, propagation channels, etc.)
• Determination and consideration of other relevant acoustic information such as background noise as a result of climatological noise (input of meteorological parameters such as sea state, wind, rain, etc), of merchant traffic or off-shore activities (input from charts of noise sources), and biological activities (input from charts and tables with seasonal and daylight dependence)
• Selection of the relevant threat information
• Determination and display of the vessel’s actual acoustic vulnerability and any subsequent vulnerability alarms
• Display and analysis of the trend factors relevant to the tactical situation, and hence for determining the optimum course of action
• Running of simulations of possible solutions and confirmation of the most effective manoeuvres to optimally counter a threat. Such simulations may consider command decisions regarding route, speed, alteration of the operational state, activation of noise modifiers or CM deployment