Acoustic profile

Resonant Acoustic Profiling (RAP ) and Rupture Event Scanning (REVS )... 

Fig. 15.11 Sediment-acoustic profile (PARASOUND) of the continental slope off die coast of Uruguay (Bleil and participants 1994). A sediment avalanche is recognizable below deposited as a compact sediment. The sediment core GeoB2809 also originated from diis profile, including die pore water profiles shown in Fig. 15.12. (see also Hensen et al. 2003).

A subbottom acoustic profile appears to give a cross section of the strata beneath the seafloor. However, it is really a plot of time that it takes the sound to pass from a ship to a reflector and back again versus clock time. An ideal profile is obtained if the spacing of soimd pulses is always the same, pulses are short, and little drift in the electronics is experienced. These conditions are usually satisfied by modem profiling systems. 

In addition to rough classification, acoustic profiling can provide some information on overconsolidation. The removal of overburden may appear as truncated or outcropping reflectors because of the effect of overconsolidation. Beds with regular reflectors parallel to the seafloor would be less likely to be overconsolidated and, therefore, weaker. An ideal can also be obtained if corrections can be made for deviations from these items. 

Chirp-Acoustic-Profiler This system is a development of a sub-bottom-profiler, and can - due to the use of external hydrophone arrays - achieve resolutions of 8 -10 cm. The data is being displayed in real time and gives a multi-colour representation of the layering of the sediments on the seabed. Objects buried into the sedimentation layer will resolve with the same accuracy so that size and shape can be evaluated. The datasets are available in a variety of formats so that compatibility with other data sources can be achieved... 

Progress has been made in the field of applied mathematics to invert this relation for the application mentioned here by techniques that establish a transformation between the data and the characteristics of the operator that describes the development of the ultrasonic field. To give the reader some insight, a sketch of an appropriate procedure for relating the measured acoustic field to the data is presented. The medium is characterized by an acoustic profile ... 

So the Fourier transform of the data equals the two-dimensional Fourier transform of the acoustical profile 0(r) on a halfcircle. By selecting different directions of s and 1 the Fourier transform of 0(r) can be found for a large number of points. The inverse transformation finally will lead to 0(r). For k- > (wavelength —0) the radii of the halfcircles tend to go to infinity and the well known result of reconstructive tomography is found the one-dimensional fourier transform of the projected data is equal to a slice through the two-dimensional Fourier transform of the projected object. 

---