Surface and volume backscattering of broadband acoustic pulses normally incident on the sea floor: Observations and models

When a broadband (1–10 kHz) impulsive (0.2‐ms duration) acoustic source is directed vertically at the sea floor, the resulting echo contains a significant proportion of energy which does not remain coherent during horizontal translations of the acoustic system. This indicates that scattering is taking place. The scattering effects are a function of frequency, and the interaction of the source beam function with the bottom produces a time dependence as the expanding wave front encounters the sea floor at an increasing distance off the axis of the source. These effects can be displayed in a contour diagram of signal power as a function of time and frequency, called a sonogram. By using models of surface and volume scattering, a synthetic sonogram can be calculated from parameters of volume scattering and surface roughness. Such a synthetic sonogram can be fitted to an actual sonogram, yielding estimates of the parameters. These parameters promise to be useful in characterizing sediments, their acoustic prop...