海底沉积物原位声学信号提取技术研究

IOCAS-IR > 海洋地质与环境重点实验室

	海底沉积物原位声学信号提取技术研究
	张严心
学位类型	硕士
导师	郭常升
	2017-05-25
学位授予单位	中国科学院大学
学位授予地点	北京
学位专业	地质工程
关键词	海底沉积物
摘要	海底表层沉积物作为海水与海底的分界面，具有独特的声学特性。海洋沉积物在各个海域和沉积环境中的声学特性对水下声环境和海底探测至关重要，而获得精确的海底沉积物声学参数是声学特性研究的前提。海底沉积物声学原位测量技术是在不改变沉积物原始状态下获得其声学参数的方法，是开展海底沉积物声学特性研究的有效手段。而无论是原位测量还是取样测量，都需要通过提取声波时差来计算声速。声波到达接收换能器的时间，即首波到时的准确判读，是准确计算声波时差，进而计算声速的关键。本文以原位测量数据为例，探究海底沉积物声学信号的提取方法。首波到时提取的难点在于：首波的幅度很小，容易和噪声混淆。在读取声波起跳点时，以往一般采用人为选取起跳点的方式。但是，人工法读取起跳点效率较低，而且人为操作容易产生读数误差。为提高读取效率和避免此类误差，需要设计合理的算法来实现对首波到时的提取。本文选择了电平门槛法、短窗- 长窗能量比法和互相关法来对时差进行提取。依托于胶州湾及青岛近海的海底沉积物原位测量数据，对几种声波时差计算方法进行了有效性分析。对比了三种方法的提取结果，发现互相关法计算不够准确，将其改进后，三种方法的计算结果非常接近。相比于人工识别的方法，基于程序计算的电平门槛法、长窗- 短窗能量比法和互相关法能够更高效提取得到声波时差。利用水池实验和海水声速经验公式计算得到的海水声速，与三种时差提取方法对水中声速的计算结果进行对比，进一步验证了三种方法的适用性。验证结果表明，三种方法都可以应用于海底沉积物原位声学信号提取。利用这几种方法对胶州湾及青岛近海45 个站位的海底沉积物原位测量数据进行处理，得到了研究区域的声速分布规律。根据研究区域的沉积物分布规律，发现声速与沉积物类型有明显的相关关系，沉积物声速随平均粒径的增大而增大。
其他摘要	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.
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/136634
专题	海洋地质与环境重点实验室
作者单位	中国科学院海洋研究所
第一作者单位	中国科学院海洋研究所
推荐引用方式 GB/T 7714	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.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
毕业论文终稿-1.pdf（3181KB）	学位论文		限制开放	CC BY-NC-SA	浏览