SOUND-SCATTERING BY ROUGH ELONGATED ELASTIC OBJECTS .3. EXPERIMENT

Measurements of the acoustical backscattering from a long randomly rough stainless steel cylinder immersed in water are presented to quantitatively illustrate the effects of small scale surface roughness. The cylinder radius varies along its lengthwise axis creating one-dimensional rotationally symmetric roughness (rms variations approximately 1% of mean radius). Using recently published rough cylinder formulations [T. K. Stanton, J. Acoust. Soc. Am. 92, 1641-1664 (1992) and T. K. Stanton and D. Chu, J. Acoust. Soc. Am. 92, 1665-1678 (1992)], explicit approximate expressions are derived for the backscattered field for the laboratory pulse-echo environment: spherically spreading directional source and receiver with arbitrary beam patterns. The actual target surface profile is well described and used as input in the numerical simulations. Agreement is found between measurements and simulation predictions both in the mean field levels and the field fluctuations over a wide range of (geometric scattering) frequencies. Roughness-induced effects such as decreases in the overall levels and pulse spreading of echoes from the front interface and circumferential waves are illustrated.