|Place of Conferral||北京|
Seafloor surface sediments, as the interface between seawater and seabed, have
unique acoustic properties. The acoustic properties of seafloor sediments in various
sea areas and sedimentary environments are critical to the underwater acoustic
environment and marine detection. It is prerequisite to obtain the accurate acoustic
parameters of seafloor sediments for the study of acoustic properties. The in situ
acoustic measurement technique of seafloor sediments is an effective method to
obtain the acoustic parameters without changing the original state of sediments. The
data measured by the in situ measurement system is calculated by extracting the
time difference of the acoustic wave. Accurate interpretation of the travel time at
which the acoustic wave arrives at the receiving transducer is the key to calculate the
time difference of the sound wave and calculate the acoustic velocity.
The difficulty to extract the arrival time of head wave is: the amplitude of head
wave is very small, which is easy to be confused with noise. In the past, it was often
done by artificial observation to select the starting point of the head wave. However,
manual method to read the starting point is less efficient, and man-made operation
prone to result in error data. In order to improve the reading efficiency and avoid
such errors, it is necessary to design reasonable algorithms to obtain the time
difference. In this paper, level threshold method, short window - long window
energy ratio method and cross correlation method are used to extract the time
difference. Based on the in-situ measurement data of seafloor sediments in Jiaozhou
Bay and Qingdao offshore region, the effectiveness of several time- difference
calculation methods was analyzed. Compared with the calculation results of three
methods, it is found that the cross correlation method is not accurate enough. After
ameliorating the method, the calculation results of the three methods are very close.
Compared with the method of manual recognition, the window threshold methodbased on program calculation, long window-short window energy ratio method and
cross correlation method can be more efficient extraction of acoustic time difference.
The results show that the applicability of the three methods is verified by comparing
the results of the three time difference extraction methods with water velocity
calculated by the pool experiment and the empirical formula of seawater velocity.
The results show that all three methods can be applied to the in situ acoustic signal
extraction of seabed sediments.
Using these methods, the in situ measurements of seabed sediments at 45
stations in Jiaozhou Bay and Qingdao offshore were processed. And the velocity
distribution of the study area was obtained. According to the distribution law of
sediments species, it is found that the sound velocity has a significant correlation
with the sediment type. It is found that the velocity of the sediment increases with
the increase of the mean grain size.
|张严心. 海底沉积物原位声学信号提取技术研究[D]. 北京. 中国科学院大学,2017.|
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