Abstract:
A thin wedge design anechoic lining has proven to be very effective for long time signature measurements at frequencies above 10 kHz. Partial treatment on five of six surfaces in a 60x40x35-ft[sup 3] depth tank resulted in accurate transfer functions of a test transducer using late sample delays for long-time signature waveforms. Comparison of data resulting from delays prior to wall/surface reflections with delays as late as 200 ms revealed negligible contribution, if any, from reflections. The ``reflection'' data when graphed over ``free-field'' data were indistinguishable. Tests were run using a directional array projector and a horizontally omnidirectional projector. The hydrophone was an H-52; a 5.1-cm vertical line array, omnidirectional in the horizontal plane. This allowed some discrimination from surface and bottom reflections. Reflections from the untreated wall were strong contributors while using the omnidirectional projector and were revealed in radiation patterns of the directional array. These tests under real world everyday measurement conditions demonstrate the effectiveness of the panels for long pulse times with late delay sampling in constrained boundaries.