Effects of changing roughness on acoustic scattering: (2) anthropogenic changes

Deliberate modification of bottom roughness, including smoothing to eliminate centimetre scale natural roughness and raking to induce quasiperiodic roughness, was investigated using diver observations, quantification of bottom roughness from stereo photography, and measurement of acoustic backscattering strength. At 40 kHz, raking perpendicular to the acoustic line-of-sight with a tine spacing equal to one-half wavelength increased scattering by 12-18 dB, which decayed to background levels within 24 hours due to biological modification of seafloor roughness. Raking parallel to the acoustic line-of-sight had little effect. Measured and modelled acoustic scattering strengths are not in total agreement suggesting, a failure of perturbation theory for these roughness conditions.