Design of a 3D Chirp Sub-bottom Imaging System

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz) that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with each hydrophone group containing four individual elements and a pre-amplifier. After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software aboard the acquisition vessel. The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface.     

海洋石油管线探测多波束剖面声纳设计

针对海洋石油管线探测多波束剖面声纳的高速、大容量的实时信号处理任务,以及声纳系统进一步扩展的需求,设计并实现了一种基于IP网络互连的、以并行DSP为处理节点的多波束剖面声纳系统.该系统应用于海底石油管线探测与定位,系统中的每个处理节点与数据采集转换部分采用TCP/IP网络连接,可以通过物理上添加一个或多个处理节点成倍的提高系统的信号处理能力,而在软件上无须大的改动.通过电联调与水槽试验,验证了系统的可行性和稳定性,该设计为高速水声阵列信号实时处理系统提供了一种全新的解决思路.     

深海内波空间啁啾的演变研究

根据基于两层流体推导的深海内波弱非线性薛定谔(Nonlinear Schrodinger,简称NLS)方程,引进空间啁啾的思想,研究深海区频散效应和非线性效应的作用。文中推导出了频散效应和非线性效应所致啁啾的表达式,采用数值计算方法计算了综合效应产生的总啁啾。分析了频散和非线性以及综合效应所致啁啾在深海内波传播中的演变规律。从空间啁啾的角度,解释中国南海东沙群岛附近深海区内波演变的机理。     

Offshore sand sources for beach replenishment: Potential borrows on the continental shelf of the Eastern Gulf of Mexico

Erosion of sandy beaches is a worldwide problem that elicits innovative geoengineer‐ing techniques to reduce adverse impacts of shoreline retreat. Beach replenishment has emerged as the “soft”; shore‐stabilization technique of choice for mitigating beach erosion. This method of shore protection involves the addition of sand to the littoral sediment budget for sacrificial purposes. Because inland sand sources are often uneconomical or impractical to use, and known nearshore sources are limited, finding adequate quantities of suitable sand on the inner continental shelf is often vital to beach replenishment projects. The technical studies of survey and materials analysis that identify and delineate usable sand sources are sometimes almost as expensive as small‐project dredging, pumping, and placing the sand on the beach as fill. Inadequate quantity or substandard quality of shelf sand, as well as often‐prohibitive overhead expenses, thus compel shoreline managers to seek suitable sand sources offshore.

In the study area off the central‐west coast of Florida, offshore potential borrow areas (PBAs) were identified on the basis of studies conducted in reconnoitory and detailed phases. Sophisticated state‐of‐the‐art equipment used in this investigation provided more detailed subbottom mapping information than is normally obtained with conventional seismic equipment. An example of sand exploration studies was incorporated in a 215‐km² survey of offshore areas by conducting bathymetric surveys and subbottom seismic profiling, collecting jet probes, grab samples, and vibrocores, and analyzing sediment grading in subsamples from vibrocores. These combined analyses indicated that at least 8.8 ×10⁶ m³ of sand is available in potential borrow areas from 7.0 to 12 km offshore in water depths of 8.0 to 11.5 m. In the PBAs, mean grain size of sand falls into the range 0.13–0.53 mm, sorting averages 0.65–1.31ø, and the overall silt content varies from 3.9–8.5%. High silt contents (13–19%) mapped in some areas make these sedimentary deposits unsuitable as fill for artificial beach renourishment.     

一种捷变调频斜率极性和限幅相结合的SAR抗干扰方法

针对合成孔径雷达（SAR）系统面临的场景散射等干扰无法使用传统时、空、频域技术抑制的问题,提出了一种基于线性调频（LFM）信号调频斜率极性捷变和限幅过程相结合的抗干扰方法。该方法首先在慢时间域捷变雷达发射信号的调频斜率极性,其次在接收脉冲后首先对转发的干扰信号进行匹配、限幅,然后在逆滤波之后正常成像。仿真验证了捷变方法的抗干扰性能。     

脉冲内拉曼散射所致啁啾的研究

探究孤子自频移现象,从啁啾的角度来解释其产生的原因。运用数学求解及数值模拟方法,通过MATLAB编程画出了啁啾演变图,据此来研究自频移现象。研究结果表明,在高阶非线性效应中,脉冲内拉曼散射、色散和自相位调制共同所致的啁啾,与无拉曼散射效应时产生的啁啾相比,发生一系列新的变化:啁啾的中心发生漂移且图形的前后沿不对称,即负啁啾的峰值的绝对值大于正啁啾的峰值,这说明了脉冲频谱“红移”的谱峰变宽,或者说频谱移向了长波长方向—即人们所说的孤子自频移现象。     

前视双基地SAR CS成像算法

提出了前视双基地SAR CS成像方法。首先研究了前视双基地SAR的成像机理,并建立了信号模型;然后通过时域线性距离徙动补偿将前视双基地SAR进行单站固定等效,并分析了回波信号等效后的方位空变性特点;在此基础上,确定了前视双基地SAR CS成像算法的相位匹配函数;最后通过算法仿真验证了算法的正确性。     

宽带啁啾脉冲激光非线性传输过程中的时空微扰研究

基于非线性薛定谔方程推导出大啁啾脉冲的传输方程,利用微扰理论,分析了啁啾脉冲激光的时空不稳定性. 理论上比较清楚的阐述了宽带脉冲激光在大啁啾情况下,其时空噪声的相互影响与相互作用情况及脉冲啁啾对噪声微扰调制的影响,发现在相同γI₀(非线性系数与峰值强度乘积)的情况下脉冲啁啾对噪声调制的增长没有直接影响. 最后我们在实验上利用非线性介质对啁啾脉冲的空间小尺度自聚焦过程进行了部分验证,同时也在数值上对宽带啁啾脉冲的时间噪声调制的增长进行了模拟分析,发现实验结果和模拟分析结论     

光子晶体光纤中零色散点处超连续谱演变的研究

从非线性薛定谔方程出发,采用分步傅立叶分析方法数值模拟光子晶体光纤中超连续谱的产生,计算、模拟并分析初始啁啾在光子晶体光纤的零色散点对超连续谱演变和带宽的影响.结果表明,非线性作用使频谱分裂成多峰不对称的结构,初始啁啾C的引入能明显的改善超连续谱的带宽和平坦性.由于二阶色散β2=0,三阶色散猹对超连续光谱的展宽影响较大.当β3>0时,C取正值时,随着C的增大,带宽减小; C取负值时,带宽有所增大,平坦性也有改善;β3<0时,无论C取正取负,频谱带宽增大,且平坦性较好.     

精密控制震源发射信号设计方法研究

考虑到精密控制震源特点,研究了多种精密控制震源发射信号的设计方案,并提出离散点拟合精密控制震源信号设计方法.计算表明,按照发射频谱、相关子波形态和发射能量3个方面的评价,离散点拟合精密控制震源信号设计方法可以灵活设计出比较好的精密控制震源发射信号,对提高精密主动地震监测的震相信息分辨率具有实际意义.