As the highest resolution seismic system available, the automated seafloor classification system (ASCS) can remotely and accurately map sediment properties for many seafloor applications. The ASCS can accurately predict, in near-real time, sediment type and a number of selected geotechnical properties of the upper several meters of the sea floor while in an underway survey mode.

An ASCS Display depicting seafloor sediment properties such as structure and type, as well as geotechnical properties such as density, porosity, and shear strength.

This system functions as a flexible research data acquisition platform for collecting data. The record produced can be used to predict sediment structure and type, as well as such properties as attenuation, density, porosity, shear strength, compressional and shear velocity, and mean grain size.

The ASCS software displays each of these sediment properties in near-real time in the format shown in the figure, or as a scrolling tabular display of numerical values. The system also allows simultaneous collection of coregistered sidescan sonar data. This feature gives a three-dimensional look at the upper meters of the sea floor. It can display the digitized acoustic return as a function of amplitude vs. time. The device has extremely robust system-controlled data acquisition, storage, and processing hardware and software. The system transmits an acoustic pulse, digitizes the acoustic return to 16 bits, records the raw data on a removable-media hard drive, and shows three different displays in near-real time.

The ASCS system normally operates at 15 kHz. It measures, both quantitatively and qualitatively, the amplitude (echo strength) and pulse characteristics of the return acoustic signal in 10 adjustable-width time windows that correspond to depth increments in the sediment. The ASCS produces a high-resolution analog seismic record of the upper few meters of the seafloor on which the amplitudes of the echo returns from the sediment's depth increments are displayed. A dedicated computer is used to store and display digitized raw echo strength and Global Positioning System (GPS) navigation data in near-real time. There is also the capability to apply algorithms based on the multilayer acoustic theory to compute acoustic impedance for each of the depth increments in the sediment. This continuous profile of acoustic impedance is then used, in combination with a series for empirical relationships, to predict sediment structure and type, as well as to predict attenuation, density, porosity, shear strength, compressional and shear velocity, and mean grain size.

Potential applications of the ASCS include:

  • Locating pipelines and other buried objects;
  • Data recording;
  • Industrial process monitoring;
  • Medical applications for anything that uses acoustic wavefronts;
  • Recording any voltage regardless of the source.

This work was done by Douglas Lambert, Naval Research Laboratory, Stennis Space Center, Mississippi. Inquiries concerning rights for the commercial use of this invention should be directed to the Office of Technology Transfer, Code 1004, 4555 Overlook Ave. SW, Washington, DC 20375-5320; (202) 767-7229; fax (202) 404-7920.

Electronics Tech Briefs Magazine

This article first appeared in the January, 1998 issue of Electronics Tech Briefs Magazine.

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