5:15 PM - 6:45 PM
[HTT18-P05] Shallow subseafloor geophysical surveys: applicability and importance of Acoustic mapping
Keywords:shallow subseafloor structure, high resolution , Geology , Offshore wind farm, acoustic mapping
Acoustic mapping is an effective imaging technique that uses acoustic signals to obtain offshore geophysical information on seafloor, and also for the shallow subseafloor environment. The acoustic mapping mainly includes topographic and backscatter intensity information in a horizontal manner. Generally a subseafloor cross-section could be obtained at a same time with the acoustic mapping, as a shallow structural investigation. Instruments are usually mounted on the bottom of a vessels on sea surface and, on a remotely operated underwater vehicles (ROV) and an autonomous underwater vehicle (AUV). Frequency used for the mapping are usually different with the thickness of the water between the instrument and target, and thus the observation results are obtained with different resolutions in different situations. The different resolution is applied for not only in the horizontal manner but also in the depth direction; we have been performed acoustic mapping with variations in the direction of depth. The different resolution in the vertical manner is theoretically acceptable but difficult to say quantitatively because of several reasons such as not-in-clear mechanics of devices, the non-uniform algorithms, and/or noises generated by instrument and environmental restrictions.
To meet the increasing demands for the use of the offshore area, information on the shallow subseafloor environments provided by the available observation techniques should be provided. For example, in the rapidly developing offshore wind farms, high-resolution geophysical information on seafloor and shallow subseafloor are important. To provide stable and long-term support for the base of wind turbines, detailed and accurate geophysical information for down to less than 100 m below the seafloor where the base of a bottom-fixed turbines or shallow subseafloor where anchored points of floating turbines are necessary. The current government-driven preliminal explorations are important. In case for offshore mining fields, there are many potential areas that have not yet been delineated. It can be said that the location where production is expected to establish mining is not enough understood yet in offshore areas. There are examples of visualized buried deposits using the acoustic mapping technique. In order to achieve zero emissions in the near future, capture and storage or utilize CO2 (CCS, CCUS) technology is said to be necessary. A storage site requires not only a stable geological setting but also the absence of localized destructive structures nor of gas migration. The presence of gas in the shallow subseafloor is clearly visualized by absorption of acoustic signals. To extract useful information for understanding shallow subseafloor environments from the results of acoustic mapping that have already been accumulated as case studies, again illustrate the potential of shallow geophysical investigations in offshore areas, share the importance of such surveys, and generate results that will contribute to expanding the use of offshore areas, should be an accelerated issue.
To meet the increasing demands for the use of the offshore area, information on the shallow subseafloor environments provided by the available observation techniques should be provided. For example, in the rapidly developing offshore wind farms, high-resolution geophysical information on seafloor and shallow subseafloor are important. To provide stable and long-term support for the base of wind turbines, detailed and accurate geophysical information for down to less than 100 m below the seafloor where the base of a bottom-fixed turbines or shallow subseafloor where anchored points of floating turbines are necessary. The current government-driven preliminal explorations are important. In case for offshore mining fields, there are many potential areas that have not yet been delineated. It can be said that the location where production is expected to establish mining is not enough understood yet in offshore areas. There are examples of visualized buried deposits using the acoustic mapping technique. In order to achieve zero emissions in the near future, capture and storage or utilize CO2 (CCS, CCUS) technology is said to be necessary. A storage site requires not only a stable geological setting but also the absence of localized destructive structures nor of gas migration. The presence of gas in the shallow subseafloor is clearly visualized by absorption of acoustic signals. To extract useful information for understanding shallow subseafloor environments from the results of acoustic mapping that have already been accumulated as case studies, again illustrate the potential of shallow geophysical investigations in offshore areas, share the importance of such surveys, and generate results that will contribute to expanding the use of offshore areas, should be an accelerated issue.