Guangming Kan

Sound velocity and related properties of seafloor sediments in the Bering Sea and Chukchi Sea

The Bering Sea shelf and Chukchi Sea shelf are believed to hold enormous oil and gas reserves which have attracted a lot of geophysical surveys. For the interpretation of acoustic geophysical survey results, sediment sound velocity is one of the main parameters. On seven sediment cores collected from the Bering Sea and Chukchi Sea during the 5th Chinese National Arctic Research Expedition, sound velocity measurements were made at 35, 50, 100, 135, 150, 174, 200, and 250 kHz using eight separate pairs of ultrasonic transducers. The measured sound velocities range from 1 425.1 m/s to 1 606.4 m/s and are dispersive with the degrees of dispersion from 2.2% to 4.0% over a frequency range of 35–250 kHz. After the sound velocity measurements, the measurements of selected geotechnical properties and the Scanning Electron Microscopic observation of microstructure were also made on the sediment cores. The results show that the seafloor sediments are composed of silty sand, sandy silt, coarse silt, clayey silt, sand-silt-clay and silty clay. Aggregate and diatom debris is found in the seafloor sediments. Through comparative analysis of microphotographs and geotechnical properties, it is assumed that the large pore spaces between aggregates and the intraparticulate porosity of diatom debris increase the porosity of the seafloor sediments, and affect other geotechnical properties. The correlation analysis of sound velocity and geotechnical properties shows that the correlation of sound velocity with porosity and wet bulk density is extreme significant, while the correlation of sound velocity with clay content, mean grain size and organic content is not significant. The regression equations between porosity, wet bulk density and sound velocity based on best-fit polynomial are given.

The development and experimental study of the Ballast in situ Sediment Acoustic Measurement System

A ballast in situ sediment acoustic measurement system (BISAMS) was newly developed. The mechanical structure, the function modules, the working principles, and a sea trial will be reported in this study. The system relies on its own weight to insert transducers into seafloor sediments and can accurately measure the penetration depth using a specially designed mechanism. The system comprises an underwater position monitoring and working status judgment module and has two operation modes: self-contained measurement and real-time visualization. The designed maximum working water depth of the system is 3000 m, and the maximum measured depth of seafloor sediment is 0.8 m. The system has 1 transmitting transducers and 3 receiving transducers. The transmitting frequency band is 20–120 kHz. The in situ acoustic measurement system was tested at 15 stations in the northern South China Sea, and the repeated measurements in seawater demonstrated good working performance. Comparison with predictions from empirical equations indicated that the measured speed of sound and attenuation matched with the predicted values and that the in situ measured data were reliable.A ballast in situ sediment acoustic measurement system (BISAMS) was newly developed. The mechanical structure, the function modules, the working principles, and a sea trial will be reported in this study. The system relies on its own weight to insert transducers into seafloor sediments and can accurately measure the penetration depth using a specially designed mechanism. The system comprises an underwater position monitoring and working status judgment module and has two operation modes: self-contained measurement and real-time visualization. The designed maximum working water depth of the system is 3000 m, and the maximum measured depth of seafloor sediment is 0.8 m. The system has 1 transmitting transducers and 3 receiving transducers. The transmitting frequency band is 20–120 kHz. The in situ acoustic measurement system was tested at 15 stations in the northern South China Sea, and the repeated measurements in seawater demonstrated good working performance. Comparison with predictions from empirical eq...

Upgrading and experimentation of the hydraulic-driven in-situ sediment acoustic measurement system

The self-contained hydraulic-driven in-situ sediment acoustic measurement system (HISAMS), developed in 2009, was upgraded with improvement of the real-time image and data collection functionality in Oct 2015. An underwater camera and some sensors are supplemented, and a new visualization and control electric unit was integrated into the updated HISAMS, which could monitor the underwater working status of the system and transmit the image and data into the onboard control panel via the coaxial cable or optoelectric composite cable. Furthermore, the maximum operating water depth of the transducer was upgraded to 3000 m by utilizing new pressure-equilibrium architecture in the system. A special field experiment was conducted to test and evaluate the upgraded system in Jiaozhou Bay, off Qingdao. This system was proven to be extensively adaptable to different sediment types and research vessel condition, and useful for in-situ determination of the sound speed and attenuation of seafloor sediment.

The sound velocity and bulk properties of sediments in the Bohai Sea and the Yellow Sea of China

In order to investigate the correlation between a sound velocity and sediment bulk properties and explore the influence of frequency dependence of the sound velocity on the prediction of the sediment properties by the sound velocity, a compressional wave velocity is measured at frequencies of 25–250 kHz on marine sediment samples collected from the Bohai Sea and the Yellow Sea in laboratory, together with the geotechnical parameters of sediments. The results indicate that the sound velocity ranges from 1.232 to 1.721 km/s for the collected sediment samples with a significant dispersion within the series measuring frequency. Poorly sorted sediments are highly dispersive nearly with a positive linear relationship. The porosity shows a better negative logarithmic correlation with the sound velocity compared with other geotechnical parameters. Generally, the sound velocity increases with the increasing of the average particle size, sand content, wet and dry bulk densities, and decreasing of the clay content, and water content. An important point should be demonstrated that the higher correlation can be obtained when the measuring frequency is low within the frequency ranges from 25 to 250 kHz since the inhomogeneity of sediment properties has a more remarkably influence on the laboratory sound velocity measurement at the high frequency.

Sound speed dispersion characteristics of three types of shallow sediments in the southern yellow sea

ABSTRACT To accurately characterize sound speed dispersion of shallow sediments in the Southern Yellow Sea, three types of sediments, i.e., silt, clayey silt, and silty clay, were selected to measure the sound speeds at 25–250u2009kHz. Over the frequency range, the sound speeds vary approximately from 1,536 to 1,565u2009mu2009s−1 in silt sediment, from 1,511 to 1,527u2009mu2009s−1 in clayey silt sediment, and from 1,456 to 1,466u2009mu2009s−1 in silty clay sediment. The sound speed exhibits a slow increase with frequency in a nearly linear gradient, but these three types of sediments have different sound speed dispersion characteristics. The silt sediment with relatively coarse grains has the most significant sound speed dispersion, while the sound speed dispersions of the two others are relatively weak. Comparison between the measured dispersions and the model predictions shows that the grain-shearing model can match the measured data at most of frequencies. Nevertheless, when the grain bulk modulus was assigned 3.2u2009×u20091010u2009Pa according to relevant references, the Biot–Stoll model predictions were higher than the measured values at high frequencies; when it was assigned a relatively small value of 2.8u2009×u20091010u2009Pa, the model predictions achieved optimal matching with the measured values.

Experimental study of the ballast in situ sediment acoustic measurement system in South China Sea

ABSTRACT The mechanical structure, the function modules, the working principles, and a sea trial of the newly developed ballast in situ sediment acoustic measurement system are reported in this study. The system relies on its own weight to insert transducers into seafloor sediments and can accurately measure the penetration depth using a specially designed mechanism. The system comprises of an underwater position monitoring and working status judgment module and has two operation modes: self-contained measurement and real-time visualization. The designed maximum working water depth of the system is 3,000u2009m, and the maximum measured depth of seafloor sediment is 0.8u2009m. The system has one transmitting transducer with the transmitting frequency band of 20–35u2009kHz and three receiving transducers. The in situ acoustic measurement system was tested at 15 stations in the northern South China Sea, and repeated measurements in seawater demonstrated good working performance. Comparison with predictions from empirical equations indicated that the measured speed of sound and attenuation fell within the predicted range and that the in situ measured data were reliable.

Laboratory measurements of sound speed and attenuation dispersion in calcareous sediments from coral reefs

The calcareous sediment is an important type seafloor sediment exist in coral reef island sea areas. The acoustic properties of calcareous sediment are significant for modeling sound propagation and underwater reverberation. In order to analyze the frequency dependence of sound speed and attenuation in calcareous sediments, the sediments were firstly screened and remodeled in plexiglass tubes in laboratory, and the sound speed and attenuation were measured at the frequency range of 27–247 kHz. The grain sizes of sediment samples were <0.075 mm, 0.075-0.5 mm, 0.5-1 mm, 1–2 mm, and 2–4 mm, respectively. The sound speeds of different grain-size sample were 1564.83–1607.36 m/s, 1564.82–1607.36 m/s, 1527.76–1553.69 m/s, 1529.40–1594.72 m/s, and 1541.87–1596.51 m/s, respectively. The attenuation were 24.94–206.35 dB/m, 20.78–208.75 dB/m, 9.66–271.94 dB/m, 12.33–310.36 dB/m, and 12.60–293.60 dB/m, respectively. The sound speeds and attenuation were found to increase remarkable with frequency. The fine grained se...

Measurement of mid-frequency acoustic backscattering from the sandy bottom at 6–24 kHz in the Yellow Sea

In a typical sandy bottom area of the South Yellow Sea, measurement of acoustic bottom backscattering strength within a frequency range of 6–24 kHz was conducted using omnidirectional sources and omnidirectional receiving hydrophones. In this experiment, with interference from scattering off the sea surface being avoided and the far-field condition being satisfied, we obtained acoustic bottom backscattering strength values ranging from −31 to −17 dB within a grazing angle range of 18°–80°. In the effective grazing angle range, the acoustic scattering strength generally increases with the increase in the grazing angle, but the variation trends were different in different frequency bands, which reflects different scattering mechanisms. The frequency dependence of the acoustic backscattering strength is characterized by a segmented correlation. In the frequency band of 6–11 kHz, the scattering strength is positively correlated with the frequency, and the average slope of the linear correlation is about 0.83 ...

In situ and laboratory acoustic attenuation measured in the sediments of the southern Yellow Sea

Acoustic attenuation directly determines sound propagation distance in seafloor sediments. Moreover, by studying the attenuation law of sound propagation in sediments, much information about sediment properties can be obtained. In June 2009 and June 2010, in situ measurements of acoustic attenuation at 30 kHz were made in the sediments of the southern Yellow Sea. Meanwhile, sediment cores were collected and laboratory measurements of acoustic attenuation between 25 and 250 kHz and physical properties were conducted. We compared in situ and laboratory attenuation measured in the sediments and analyzed the differences. The frequency dependence of acoustic attenuation of silt, silty clay, and clay is discussed on the basis of laboratory measurements. Combining with sediment physical properties, we analyzed the acoustic attenuation mechanism of silt, silty clay, and clay.

Numerical simulation of acoustic wave field of seafloor sediments based on Biot model

Based on the Biot model, Acoustic wave field of seafloor sediments are calculated and analyzed by means of finite-difference numerical simulation. According to the results, Porosity(Ø) and permeability(К) both have important influence on wave field of marine sediment. As Ø increases, velocity and amplitude of the fast wave decrease, but velocity of the slow wave increases. As К decreases, the amplitude of the slow wave decreases. In addition to reflection and transmission characteristics, the transform features of wave appear on the interface of two sedimentary layers of marine sediments. On the interface, the fast wave is transformed into the shear and the slow wave. The shear wave is transformed into the fast wave. The slow wave is transformed into the shear and the fast wave. Extraordinarily, the fast wave which transformed from the slow wave has identical properties with the usual fast wave such as a little velocity dispersion and attenuation.