Modelling Analysis of Echo Signature and Target Strength of a Realistically Modelled Ship Wake for a Generic Forward Looking Active Sonar

Modelling Analysis of Echo Signature and Target Strength of a Realistically Modelled Ship Wake for a Generic Forward Looking Active Sonar

Schippers, P.

2009

The acoustic modelling in TNO’s ALMOST (=Acoustic Loss Model for Operational Studies and Tasks) uses a bubble migration model as realistic input for wake modelling. The modelled bubble cloud represents the actual ship wake. Ship hull, propeller and bow wave are the main generators of bubbles in the wake. The bubble volume originates from the wake velocity field, combined with properties and physical processes of air bubbles in water. The bubble volume is assumed to be insonified by a generic active forward looking sonar. The resulting back-scattered sound is modelled with the recently developed ALMOST-REATES module (=Range Estimator for Active sonar and Target Echo Strength). It takes into account bubble scattering spectra and positions, and other important factors for the echo signal, like propagation loss from sonar transmitter and back to sonar receiver, beam forming, and signal processing. The new method is a further development of the ALMOST-REACT module (=Range Estimator for ACTive sonar): The active sonar equation is programmed here based on echo arrival times, computing sonar performance for point targets. The new method uses specified bubble positions, provided by the ship wake bubble migration model, to compute first the Impulse Response function. With the given spectrum of the active sonar pulse, the echo time series is modelled by simulating active sonar processing. Detection performance and an effective Target Strength for the scenario are deduced from this echo time series. The actual sonar processor is simulated, usually equipped with matched filter or straightforward energy detector. To run the model on a standard PC, the number of bubble positions is limited, while also the run time must be acceptable. The consequences of this limitation are reduced by applying some statistics in the modelling. Some results of echo structures and sonar performance are shown in a realistic active sonar scenario.

Ship wake modelling
Acoustic sonar performance
Acoustic signature
Target Strength
Acoustic modelling

http://resolver.tudelft.nl/uuid:fab6b108-9727-4d9b-8fc3-31651e036767

471632

Proceedings 3rd International Conference and Exhibition on Underwater Acoustic Measurements - Technologies & Results - UAM 2009, 21-26 June 2009, Nafplion, Greece

conference paper