Print this page


Subbottom Profiling

Examples of CSA International's Marine Field Operations Services:

Subbottom Profiling

OVERVIEW
Seismic profiling technology is the standard method employed to map geological features and locate structures below the surface of the seafloor. A subbottom profiler provides an acoustic profile of a narrow section of the subbottom directly beneath the path over which the device is towed. Subbottom profilers are impulse-type devices that transmit acoustic energy over a wide range of frequencies. Low frequency energy provides the greatest penetration while the higher frequencies and wide band widths provide higher resolution.

Approach
Continental Shelf Associates, Inc. (CSA) has used various subbottom profiling systems since 1978 in support of numerous marine and coastal surveys. Most current subbottom profiling investigations are conducted using CSA's MINI-STAR "CHIRP" Full Spectrum Digital Subbottom Profiler. This system is a wide band, FM modulated, high resolution seismic profiling device that can generate cross-sectional images of subbottom structure with a resolving power as fine as 6 cm. The system also generates quantitative output of acoustic attenuation values that can be correlated with sediment type.

Typically, this system is used in conjunction with CSA's Navigation and Data Acquisition System (NADAS). The NADAS is a modular computer software and hardware package that interfaces the subbottom profiler and various other data collection sensors with the positioning system in use. The NADAS enables the survey team to pre-plot survey lines or positions and also use the system for vessel guidance, data logging, and real-time vessel track plotting. The NADAS feeds fix marks, towfish positioning coordinates, and water depth data to the subbottom profiler system's graphic recorder, which in turn prints these data along the edges of the subbottom profiler scrolls.

In addition to being displayed and recorded on the paper scroll, the subbottom imagery also is displayed on a high resolution computer monitor as well as recorded on a Digital Audio Tape (DAT) recorder. The DATs provide backup records and also enhance post-processing, especially for the production of isopach maps showing contours of sediment thicknesses. This lightweight and portable system can be deployed manually by one or two people from a small vessel. The components are packed modularly in rugged shipping containers for economical air freight and rapid response.

Applications

  • Remote classification of seafloor sediments
  • Marine engineering geotechnical surveys
  • Pipeline/cable site investigations
  • Shallow reconnaissance geological surveys
  • Environmental site investigations
  • Sand source searches
  • Archeological (cultural resource) surveys
  • Hazard surveys for shallow gas and gas seeps
  • Harbor development
  • Geological formations mapping