3:30 PM - 3:45 PM
[SCG52-01] Development of the acoustic survey system using deep-towed or vertical cables for the seafloor resource exploration
Keywords:Seafloor resources, Acoustic survey, Deep tow, Vertical cable
For the exploration of resources, such as the hydrothermal deposits or methane hydrates, which are distributed on the seafloor and in the subseafloor, the acoustic survey using deep-towed or vertical cable is more effective than the conventional surface streamer surveys. This is because these types of systems enable to set the observation level close to the seafloor and to provide the dataset with accurate geometry and high S/N acoustigrams, compared to the surface streamer surveys. Moreover, these systems do not need to occupy a large area, so we may reduce the risk to disturb the other shipping activities.
Having been supported by the Strategic Innovation Promotion Program (SIP) launched in 2014 by the Council for Science, Technology, and Innovation (CSTI) in Japan, we have developed some sort of acoustic survey systems. During development works, we carried out several surveys in the area where the hydrothermal deposits had been discovered, and obtained subsurface images from the developed survey systems. In this paper, we present the methodology of the survey systems and the yielded subsurface images.
First, we introduce the survey systems using deep-towed or vertical cables. In the deep-towed system, the vessel towed the unit to stabilize the depth of the hydrophone cable (the deep-tow unit). When the ROV (Remotely Operated Vehicle) is employed as the deep-tow unit, it can deploy a small acoustic source. In the case of the vertical cable, the buoy generates tension to stabilize the position of the hydrophone cable. For carrying out the 3D survey, acoustic source excitation is performed with the spiral shooting, centered on the vertical cable (Fig). One hydrophone cable mounts 16 hydrophones, and the spacing of the hydrophone is vary with survey purpose. In case of the shooting from the vessel, the airguns or sparkers are used, while, in case of the shooting from the ROV, the sub-bottom profiler is used because it can be used with a small battery.
Second, we present the imaging result from some acquired datasets. Parts of the imaging results have already been reported in Katou et al., (2018), Tara et al., (2020), and Katou et al., (2021). Here, we newly show the 3D imaging results from the vertical cable survey in addition to the previously reported results and analyze the effective resolutions for each survey system. Note that we successfully obtained the seamless 3D image covering the whole survey area, by applying the mirror imaging technique which is adopted also by Jamali Hondori et al. (2019).
In conclusion, it is demonstrated that our developed two types of acoustic survey systems are suitable for the exploration of various seafloor and subseafloor resources such as hydrothermal deposits. We will try to expand the utilization of these systems to the exploration of cobalt-rich crust, rare earth mud, and the geological assessment for wind power plant construction in the future.
Acknowledgment: This work was supported by the Council for Science, Technology, and Innovation (CSTI), through the Cross-Ministerial Strategic Innovation Promotion Program (SIP) “Next-generation technology for ocean resources exploration” (Lead agency: JAMSTEC).
References:
Jamari Hondori, E., et al., (2019) Mirror reverse time migration using vertical cable seismic data for methane hydrate exploration, Geophys., 84(6), B447-460.
Katou, M., et al., (2018) Integrated seismic imaging of the deep-towed streamer survey in
the hydrothermal deposit area, Proceedings of the 13th SEGJ International Symposium, 546-549.
Katou, M., et al., (2021) Structural imaging of acoustic survey using a deep-towed sub-bottom profiler and hydrophone cable, IEEE J. Ocean. Eng., 47(2), 399-416.
Tara, K., et al., (2020) Seafloor hydrothermal deposit exploration by high-resolution acoustic survey using deeply towed hydrophone cable, BUTURI-TANSA, 73, 14-22. (in Japanese)
Having been supported by the Strategic Innovation Promotion Program (SIP) launched in 2014 by the Council for Science, Technology, and Innovation (CSTI) in Japan, we have developed some sort of acoustic survey systems. During development works, we carried out several surveys in the area where the hydrothermal deposits had been discovered, and obtained subsurface images from the developed survey systems. In this paper, we present the methodology of the survey systems and the yielded subsurface images.
First, we introduce the survey systems using deep-towed or vertical cables. In the deep-towed system, the vessel towed the unit to stabilize the depth of the hydrophone cable (the deep-tow unit). When the ROV (Remotely Operated Vehicle) is employed as the deep-tow unit, it can deploy a small acoustic source. In the case of the vertical cable, the buoy generates tension to stabilize the position of the hydrophone cable. For carrying out the 3D survey, acoustic source excitation is performed with the spiral shooting, centered on the vertical cable (Fig). One hydrophone cable mounts 16 hydrophones, and the spacing of the hydrophone is vary with survey purpose. In case of the shooting from the vessel, the airguns or sparkers are used, while, in case of the shooting from the ROV, the sub-bottom profiler is used because it can be used with a small battery.
Second, we present the imaging result from some acquired datasets. Parts of the imaging results have already been reported in Katou et al., (2018), Tara et al., (2020), and Katou et al., (2021). Here, we newly show the 3D imaging results from the vertical cable survey in addition to the previously reported results and analyze the effective resolutions for each survey system. Note that we successfully obtained the seamless 3D image covering the whole survey area, by applying the mirror imaging technique which is adopted also by Jamali Hondori et al. (2019).
In conclusion, it is demonstrated that our developed two types of acoustic survey systems are suitable for the exploration of various seafloor and subseafloor resources such as hydrothermal deposits. We will try to expand the utilization of these systems to the exploration of cobalt-rich crust, rare earth mud, and the geological assessment for wind power plant construction in the future.
Acknowledgment: This work was supported by the Council for Science, Technology, and Innovation (CSTI), through the Cross-Ministerial Strategic Innovation Promotion Program (SIP) “Next-generation technology for ocean resources exploration” (Lead agency: JAMSTEC).
References:
Jamari Hondori, E., et al., (2019) Mirror reverse time migration using vertical cable seismic data for methane hydrate exploration, Geophys., 84(6), B447-460.
Katou, M., et al., (2018) Integrated seismic imaging of the deep-towed streamer survey in
the hydrothermal deposit area, Proceedings of the 13th SEGJ International Symposium, 546-549.
Katou, M., et al., (2021) Structural imaging of acoustic survey using a deep-towed sub-bottom profiler and hydrophone cable, IEEE J. Ocean. Eng., 47(2), 399-416.
Tara, K., et al., (2020) Seafloor hydrothermal deposit exploration by high-resolution acoustic survey using deeply towed hydrophone cable, BUTURI-TANSA, 73, 14-22. (in Japanese)