Modeling the mechanical and flow-induced noise on the surface suspended acoustic receiver

The Surface Suspended Acoustic Receiver (SSAR) is a free drifting acoustic tomography reception system. Early prototypes of the SSAR exhibited very poor signal-to-noise ratios in the frequency band of the hydrophones. Analysis of accelerometer data from sea trials revealed a direct correlation between noise level and the wave-induced vertical velocity of the hydrophones. Such a correlation is strongly suggestive of flow noise and thus one approach to improving the design is simply to reduce the vertical velocities that the system experiences. This paper presents a time-domain numerical modeling approach to evaluating design changes that will reduce the vertical velocities of the hydrophones. Results for both wave following and spar surface buoys are presented. The model motion results are used with empirically determined noise-velocity relationships to predict the noise levels in a variety of sea state conditions.