| Popis: |
A sonogram expresses signal power as a function of both time and frequency. Sonograms of sea floor echoes obtained with a high resolution (0.2 ms duration) broadband (1–10 kHz) sound source show effects of surface scattering at the sea floor, frequency selectivity of some subbottom reflectors, and the frequency dependence of sound attenuation in the sediment. By assuming attenuation to be proportional to frequency, sonograms of some subbottom reflectors (targets) yield an estimate of the attenuation in the overlying sediment. The quality of these estimates depends on the frequency range over which a good signal-to-noise ratio exists, the interference of scattered energy with the target reflection, knowledge of the transmitted pulse spectrum, and the frequency characteristics of the target. The estimates of attenuation tend to be lower than those obtained by other workers using samples and in situ probes, but this may be due to the depth of burial. |
