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At extreme deep-sea pressure, the assessment of the electroacoustic conversion performance of transducers is a major problem, particularly in the acoustic exploration of seabed sediment in 11,000-m abysses. To address this problem, an online measurement method was proposed for the electroacoustic performance under extreme pressure. The method utilized the 11,000-m transceiver with the high-frequency and narrow-beam characteristics. In the full-depth pressure profile, the transceiver signal was measured online by an extreme pressure simulation device. At different extreme pressure sites, characteristics of the transceiver signal were analyzed using the transceiver signal at atmospheric pressure as the reference. The characteristics included amplitude response characteristics, frequency response characteristics and time-frequency characteristics. The 11,000-m transceiver has verified the stability and reliability of its electro-acoustic conversion performance. It was also analysed the effect of the transducer on the calculation of seabed sediment parameters in a pressure environment. [ABSTRACT FROM AUTHOR]

We developed a high-frequency submersible sub-bottom profiler (HF-SSBP) instrument for taking deep-sea sediment measurement. In order to evaluate the reliability of profile data, a laboratory calibration method (LCM) was developed using illuminated acrylic standard boards in anechoic tank to form multi-layer reflections and evaluate the errors of the HF-SSBP. Two layer reflections induced by single boards in different thicknesses and ranges were performed and recorded, after which four layer reflections induced by two boards with an adjusted water crack were set and logged. The results showed that the HF-SSBP resolution was 44.9 mm in acrylic and its equivalent in the sediment was 28.5 mm. The absolute measure error was 7 mm with an acrylic board thickness of 100 mm, and the maximum measure error was 3.5 mm in different water thicknesses. As a test and application, deep-sea sediment measurement of the HF-SSBP was launched and compared with in situ sampling cores in the same site. The measurement thickness for sections A and B are 39.4 cm and 23.2 cm, respectively, corresponding to the sampling core of 39.8 cm and 23.7 cm. The two results are close as we expected. This work demonstrates the reliability and accuracy of the HF-SSBP measurement, thus providing a good choice for deep-sea submergence vehicles to carry this sonar instrument to obtain high-resolution stratum in deep-sea surficial sediments. [ABSTRACT FROM AUTHOR]

In the study of sedimentary acoustics, measuring sound speed in the first layer sediment is a key issue. To solve this problem, we proposed a method for measuring the sound speed in the deep-sea first-layer sediment using a high-frequency submersible sub-bottom profiler. In this method, we obtained the reflection data of deep-sea sediments near the bottom using a wide-band narrow-beam single transducer and obtained the profile of deep-sea sediments using the reflection compression method. The first sediment layer was extracted according to the layer structure information, and the sound speed of the first sediment layer was directly measured. The transducer feasibility of the high-frequency submersible sub-bottom profiler operating at high pressure in deep sea was verified through high hydrostatic pressure tests in the laboratory. We designed a laboratory reflection compression measurement device to simulate the first layer of deep-sea sediments and verified the effectiveness of the measurement method. This method also was used to process deep-sea sediment data acquired by the Deep-Sea Warrior manned submersible. [ABSTRACT FROM AUTHOR]

Sub-bottom profiling traditionally uses low-frequency signals (less than 20 kHz) to examine layered structures of the bottom sediment in large depth, but it has some limitations in deep-sea surveying. The surficial sediment within several meters under the water–sediment boundary in the deep sea cannot be distinguished clearly. In this study, a high-frequency sub-bottom profiler (HFSBP) was developed and applied to a manned deep-submergence vehicle (DSV), named Deep-Sea Warrior, to obtain a centimeter-level resolution stratum of several meters in the deep-sea surficial sediment. Twelve diving tests were carried out, the diversity of surficial benthic profiles on the northern slopes of the South China Sea was shown up for the first time and as many as four layers profiles were obtained in the low bending canyon region, rock surface profiles, discontinuous stratum structures and thick surficial sediment in the deeper region. Continuous and clear stratum structures within a range of about 2 m on the seabed surface sediment were obtained in 11 of the 12 dives. As the dive sites took a certain dispersive distribution, it reflected that the stratum structure of surficial sediment was prevalent in the northern slopes area of the South China Sea for the most part. To verify the effectiveness of HFSBP, a laboratory test in an anechoic tank was performed, and the experiment results verified the layered ability and the thickness measurement stability of it. The comparison was performed with shipboard data of deep-sea sub-bottom profiler (SBP) Bathy-2010, and the HFSBP results were obviously better than those of Bathy-2010 measurement. The clear and continuous fine layered data obtained by HFSBP may help scientists in new area research in marine geophysics. [ABSTRACT FROM AUTHOR]