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[AS-01] A case study on the penetration difference of acoustic signals into sediment due to frequency based on backscatter strength distribution obtained along the Kumano Basin Edge Fault Zone
Acoustic mapping such as bathymetry and backscatter strength observations are applicable and useful geophysical explorations that can be easily obtained. Unlike bathymetry data, backscatter strengths are difficult to use and discuss in-depth because they often output relative values perceived by each device. However, the relative distribution of backscatter strength data obtained by a particular environment is enough for discussing the variation in the acoustic characteristics of the target.
During the same amount days and in the same area, acoustic mapping was conducted using different equipment (research vessel and AUV) with different signal frequencies (12 kHz and 120 kHz for backscatter strength distribution, respectively). The topographic data show a similar trend between different frequencies because of gridding creation, whereas backscatter strength distribution displays different patterns: backscatter strength obtained by AUV shows larger variation over the seafloor than shipboard observation. Although it is difficult to make direct comparisons of strength distribution between different equipment, the difference may be not only due to difference of resolution of acoustic signals, but also different penetration depths into the sediment. Such different patterns are expected when there is a marked difference in materials below the shallow seafloor where low frequency can penetrate sediment, such as an offshore mud volcano field in sedimentary basins.
During the same amount days and in the same area, acoustic mapping was conducted using different equipment (research vessel and AUV) with different signal frequencies (12 kHz and 120 kHz for backscatter strength distribution, respectively). The topographic data show a similar trend between different frequencies because of gridding creation, whereas backscatter strength distribution displays different patterns: backscatter strength obtained by AUV shows larger variation over the seafloor than shipboard observation. Although it is difficult to make direct comparisons of strength distribution between different equipment, the difference may be not only due to difference of resolution of acoustic signals, but also different penetration depths into the sediment. Such different patterns are expected when there is a marked difference in materials below the shallow seafloor where low frequency can penetrate sediment, such as an offshore mud volcano field in sedimentary basins.
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