Deep-towed High Resolution multichannel seismic imaging

High Resolution (220–1050 Hz) seismic acquisition performed in deep water using deep-towed systems provides unrivalled lateral resolution when compared to conventional surface seismic. The lateral resolution of these acquisitions is controlled by the width of the first Fresnel zone, taking advantage of their positions close to the sea bottom. No current existing deep towed equipment can benefit from seismic imaging processing techniques to improve this resolution as a consequence of positioning inaccuracies. The technological developments of a digital deep-towed multichannel streamer are presented with a particular attention to positioning: each hydrophone incorporates a pitch, roll and heading sensor in order to monitor the constant deformation of the streamer in operation. The sea trials took place in July 2013 in the Mediterranean Sea. Pre-stack depth migration applied to the deep-towed multichannel data illustrates the potential of this emerging methodology in terms of penetration (12 dB improvement in Signal/Noise) and lateral resolution (mean signal wavelength: 3 m) when compared with deep-towed single-channel acquisition.     

Spatial smoothing and minimum variance beamforming on data fromlarge aperture vertical line arrays

Various approaches to the beamforming of data from large aperture vertical line arrays are investigated. Attention is focused on the conventional beamforming problem where the angular power spectrum is estimated, in this case by the adaptive minimum variance processor. The data to be processed are 200 Hz CW transmissions collected at sea by a 900 m vertical line array with 120 equally spaced sensors. Correlated multipath arrivals result in signal cancellation for the adaptive processor, and spatial smoothing techniques must be used prior to beamforming. The processing of subapertures is proposed. Full aperture and subaperture processing techniques are used on the 200 Hz data. Multipath arrivals are found to illuminate only parts of the array, thus indicating that the wavefield can be highly inhomogeneous with depth     

东海南部二维地震勘探采集参数研究

东海南部油气勘探已有三十多年。经过多年研究认为,东海南部分布广泛的中生代沉积盆地具有较好的勘探前景。以往研究是以浅部新生界为主要目的层,地震采集参数存在电缆短、震源能量小、沉放深度浅等问题,获得的地震数据深部品质低。此文通过对该地区以往采集参数分析,地震剖面对比及主要参数的研究,制定了试验方案,并通过外业试验对比分析,确定了最终的采集参数,取得了良好的地震资料。研究结果表明,电缆拖带长度长（理论上最好9000m）．气枪容量大,电缆和震源的沉放深度深更有利于获得深部中生界的有效反射。     

斜缆宽频宽方位地震资料处理关键技术在西湖凹陷P气田的应用

西湖凹陷P气田应用斜缆宽频+多船宽方位的采集方式,产生了连续变化的鬼波陷波频率,最大程度地压制了鬼波,得到了高信噪比和高保真度的宽频宽方位地震资料。针对西湖凹陷P气田斜缆宽频地震资料,采用了子波零相位化及去气泡处理技术,一维滤波算子求逆有效压制震源鬼波技术和稀疏 τ-p反演方法有效压制接收器鬼波技术,有效地去除了多次波,拓宽了低频和高频信息,提高了地震资料的信噪比和分辨率。通过对实际资料对比分析,认为此方法可以得到较好的处理效果,可以提供较为真实的地震剖面,从而更好的指导生产。     

参量阵浅地层剖面的处理方法及在识别浅层天然气水合物中的应用

近年来,参量阵浅地层剖面以其简便的野外采集方式、高分辨率的浅部地层成像能力,迅速发展为海底浅层天然气水合物探测的有效方法。为了更好地获取东海浅层天然气水合物赋存区的地质信息,针对参量阵浅地层剖面数据开展了精细化处理。首先将异常振幅压制和空间振幅均衡等方法有机结合,解决了数据中的各种噪音和能量不均衡等问题,然后利用Hilbert变换提高地层分辨率,最后利用信号增强技术进一步提高同相轴连续性,获得了波组特征更清晰的地震剖面。处理后的参量阵浅地层剖面具有信噪比较高、连续性好、地层结构清晰等特点,可以更好地揭示空白带、气烟囱、亮点和火焰状异常等地震反射特征,为识别浅层天然气水合物赋存区地质信息奠定基础。对精细处理后的数据进一步开展曲率属性、瞬时振幅属性、相干属性等地震属性分析,结果显示,与浅层天然气水合物渗漏相关的声学异常能够被清晰地识别出来。此项研究一方面验证了参量阵浅地层剖面数据处理方法的可行性,另一方面也探索了属性分析技术在海底浅层天然气水合物识别方面的应用。     

A high-resolution seismic profiling system using a deep-towed horizontal hydrophone streamer

A seismic reflection profiling system utilising a surface air gun source and a deep-towed horizontal hydrophone streamer has been developed for high resolution studies in the deep ocean. The instrument is deployed on a conventional armoured single conductor cable at depths of up to 6 km. Seismic data from the 30 m long streamer is wide-band frequency modulated up the towing cable to the ship together with a high frequency monitor from a 3.5 kHz echo-sounder mounted on the instrument package. The geometry of the system allows an order of magnitude improvement in spatial resolution compared with that obtained from standard surface source/receiver configurations. The summed hydrophones of the streamer attenuate cable-generated mechanical noise, and the 3.5 kHz sea-surface and bottom reflected returns provide receiver positioning information. The system has been successfully deployed at depths of 5 km in the Vema Fracture Zone in the North Atlantic, and although initially difficulties were experienced in balancing the streamer, subsequent profiles across the transform fault show details of sub-bottom structure which on conventional surface records are generally masked by diffraction hyperbolae.     

水声信道高速率数据传输技术

本文介绍近年来水声信道高速率数所传输技术的一些研究进展，并结合本所研究的水声数据遥测，数字语音通讯和视频图像传输实验样机，讨论了具有抗多途干扰的声传输系统在调制信号设计及信号处理上所采用的关键技术。     

A case study: imaging OBS multiples of South China Sea

The subseafloor structure offshore South China Sea was imaged using first-order water-layer multiples from ocean-bottom seismometer data and the results were compared to conventional imaging using primary reflections. The mirror-imaging method employs a primaries-only reverse time pre-stack depth migration algorithm to image the receiver ghosts. The additional travel path of the multiples through the water layer is accounted for by a simple manipulation of the velocity model and processing datum: the receivers lie not on the sea floor but on a sea surface twice as high as the true water column. Migration results show that the multiple-migrated image provides a much broader illumination of the subsurface than the conventional image using the primaries, especially for the very shallow reflections. The resulting image from mirror imaging has illumination comparable to the vertical incidence surface streamer (single-channel) reflection data.     

On the determination of directional wave spectra for practical applications

The performance of various directional instruments for practical oceanographic and coastal engineering applications is examined. The emphasis is put on the application of conventional current meters equipped with high resolution pressure sensors and three element arrays. Two simulation techniques have been used to produce input data with known frequency spectrum and known directional spreading. The directional spreading is determined by the maximum likelihood method and the resulting spreading is compared with the input spreading. The performance of a conventional current meter equipped with a high resolution pressure sensor depends on the width of the directional spreading of surface waves and on the frequencies under consideration. Even for very narrow directional spreading, the current meter response is acceptable for practical applications and for shallow water deployment. In general, the current meter directional response does not depend on the direction of the incident waves. The spatial array of three wave staffs deployed in shallow water shows a similar performance to that of the current meters when the dimension of the spatial array is of the order of 1 m. This performance also does not depend on the direction of the incident waves.     

A Sound Approach to Soft Sediment Resolution

The last few years has seen a surge in research activities directed towards investigating properties and dynamics of young marine, limnic and fluvial sediments. It is by now a well established fact that the sequence of sediments ranging from concentrated benthic suspension over fluid mud to un-consolidated material summarized as liquid sediments (LS), act as carriers for a wide range of pollutants discharged or migrated into waterways. Knowledge of the transport and fate of LS allows determining the transport and fate of adsorbed constituents (e.g., heavy metals, pesticides, PCBs, PAHs). To assess the environmental impact of LS, efforts have to be made to better understand the processes in relation to hydrodynamics and the chemical and physical properties of the layers. Since physical laws limit the resolution and detection power of conventional seismo-acoustic systems in respect of LS, alternative measurement, data analysis and processing approaches have to be found. Adapted acoustic procedures initially developed for shallow water marine environments to extreme shallow water regimes using matched field inversion techniques can reveal geoacoustic parameters including density, compressional wave speed and attenuation as a function of depth and time. The paper outlines the effects of sediment mobility upon the environment followed by a short overview of techniques commonly used to investigate sediments and other freshwater/marine events. The problems faced and limitations of existing systems are briefly outlined. Results obtained with recently developed and refined geoacoustic inversion methods are presented highlighting their potential for long-term study of physical properties and dynamics of LS.     

高分辨率三维地震处理技术及其在浅层地质灾害评估中的应用

常规三维地震资料处理是以寻找深层油气为主要目标而设计的流程,在利用三维地震资料进行浅层地质条件评价和地质灾害评估时,需要针对浅部目标层进行高分辨率处理方法的研究。通过处理试验,发现影响浅层分辨率的处理参数与深层不同,从而确定了浅层处理中的最优参数;通过对琼东南盆地1 248 km2的三维地震数据利用不同偏移距进行处理,形成了3种地震数据体。通过对3种数据体的分析比较及综合考虑分辨率与信噪比后,选用偏移距250~1 650 m的数据体进行解释研究,确定浅层地质条件,评估潜在的地质灾害。     

小排列高分辨多道地震系统在岱山岛大桥工程中的应用

对运用小排列高分辨多道地震系统获取的岱山岛大桥附近海域高精度的地震数据进行了综合分析和处理,查明了调查区域的工程地质条件,并对两个桥址方案进行了地质条件的对比。采用的地震系统参数:拖缆为24道,道间距为2 m,偏移距为46 m,枪容积为10 in3,频带范围为1~1 000Hz。结果表明:(1)采用了统一方法和流程对岱山岛大桥工程中所获得的地震数据进行分析、处理,保证了两种选址方案调查结果的一致性。(2)舟山本岛-岱西桥位(方案Ⅰ)和舟山本岛-双合山桥位(方案Ⅱ)海底地形平缓,不存在海底滑坡体等不良地质现象,调查区域虽分别有6条和5条断裂,但所有断层的上覆第四系均未发生错断,断裂均为非活动性断裂,两个方案桥位线均具有建桥的良好工程地质条件。(3)与单道地震相比,小排列高分辨多道地震系统能得到更为丰富的地层反射地震数据,而该系统比传统的多道反射地震方法具有作业方便、经济的优势,可见,该调查方法适用于近岸区域浅水工程环境的地质调查工作,是一种方便、实用和经济的地质调查手段。     

High-resolution beamforming by the Wigner-Ville distribution method

The Wigner-Ville distribution (WVD) function was originally proposed by Wigner in quantum mechanics and Ville applied it for signal analysis. This method has made it possible to represent a signal's power density spectrum in the time-frequency domain as a natural extension of the Fourier transform method (FTM). Recently, it has attracted great interest for its validity to analyze time-varying signals accomplished by the development of high-speed digital signal processing, and it is used for analyzing nonstationary signals. Conventionally, a sonar beamformer is constructed using delay lines, but the development of the high-speed processor has made it possible to apply the FTM for sonar beamforming. However, the bearing resolution of the beamformer is not enough for discriminating small underwater objects on the sea bottom by this method. To solve this problem, we aim to apply the WVD method, which can represent finer structure of signals as a natural extension of the FTM, for sonar beamforming to obtain sharper beam patterns than those of the beamforming method by FTM. Simulation results by computational calculations to clarify the resolution by the WVD method, which is presented in this paper, becomes approximately twice as high as by conventional FTM. The results of an experiment at sea also show the performance of this method     

Performance limitations in underwater acoustic telemetry

Performance limitations in digital acoustic telemetry are addressed. Increases in computational capabilities have led to a number of complex but practical solutions aimed at increasing the reliability of acoustic data links. These solutions range from ocean-basin scale data telemetry to video-image transmission at a few hundred yards' distance. The opportunity to implement highly complex tasks in real time on modest hardware is a common factor. The data rates range from 1 to 500 kb/s and are much slower than satellite channels, while acceptable system complexity is higher than virtually any other channel with comparable data throughput. The basic performance bounds are the channel phase stability, available bandwidth, and the channel impulse response fluctuation rate. Phase stability is of particular concern for long-range telemetry, channel fluctuation characteristics drive equalizer, and synchronizer design; the bandwidth limitation is a direct constraint on data rate for a given signaling method     

SAMI: a low-frequency prototype for mapping and imaging of theseabed by means of synthetic aperture

The objective of the Synthetic Aperture Mapping and Imaging (SAMI) project was to develop and to test at sea a wide-band synthetic aperture sonar prototype, capable of providing high-resolution seafloor images together with bathymetry maps. This system used the motion of a physically small array in order to synthesize a longer array, providing images with an across-track resolution independent of both range and transmit frequency. Such systems are clearly very relevant to the high-precision long-range (low-frequency) imaging of the sea bottom. The project has led to the construction of a prototype tested at sea on several well-known areas for comparison with existing images and maps. These areas included several types of sea bottom, depths, and geological structures. The results obtained in real time, on-board ship, have shown the relevance of the proposed wide-band techniques. The many profiles produced have provided high-resolution images and maps of various seafloors. Interpretation by geologists showed that the system was capable of providing the same or finer detail than a deep-sea short-range, high-frequency system and maintained a higher resolution over a wider swath. The sea data processed have shown that the system provided maps with a cubic meter voxel. The resolution cell is constant over the whole range (50 to 2500 m) thanks to the dynamic focusing of the synthetic aperture. Postprocessing of a part of the data stored during the experiments has been carried out in the laboratory. This work has shown that techniques such as autofocusing can give an increase in resolution (i.e., gain in contrast and resolution of about 3 dB). The results displayed in the paper show the relevance of the techniques developed to the provision of a complete high-performance imaging tool for the oceanographic community     

希尔伯特谱白化方法在海洋地震资料高分辨率处理中的应用

针对海洋地震资料高分辨率宽频处理的要求, 也为了克服常规谱白化、反Q滤波等方法无法同时增强时域和频域局部细节的不足, 基于希尔伯特黄变换(HHT)的谱白化方法对海洋地震资料进行高分辨率处理应用研究。对地震记录进行固有模态分解(EMD), 得到不同尺度的IMF分量; 再利用常规谱白化方法对每个分量根据瞬时频率进行合理的振幅均衡; 将均衡后的IMF分量进行反变换重构地震记录, 从而得到高分辨地震数据。通过理论模型和实际地震资料实验, 与常规谱白化方法的对比分析, 表明该方法信号局部时频刻画能力以及相对振幅保真性优于常规方法, 同时表明此方法能够有效增强地震信号时域和频域的分辨率, 使地震剖面更为连续和清晰, 并具有较高的信噪比     

Adaptive multiuser detection for underwater acoustical channels

An underwater acoustic local area network (ALAN) provides multipoint-to-point telemetry between many high-rate, ocean-bottom sensors and a central, surface-deployed receiver in the 10-30 kHz vertical acoustical channel. Ocean-bottom modems initiate the transmission process by requesting data channel time slots via a common narrow-band request channel. Request packets overlap in time and frequency in this channel, and the throughput and average transmission delay rely heavily on the successful resolution of the request packet collisions. This paper presents the design, analysis, and experimental demonstration of a request channel receiver capable of resolving collisions between several asynchronous and cochannel packets. The receiver algorithm differs from standard capture schemes (by demodulating the data from both strong and weak transmitters), conventional spread-spectrum receivers (by overcoming the near-far problem), and existing multiple-access demodulation techniques (by adapting to the number of interfering signals, and the unknown phase, Doppler, amplitude, and timing of each signal in the collision). The receiver demodulates the collided packets by decision-directed techniques through a novel method of estimating the interference for each user which minimizes error propagation due to inaccurate tentative decisions. An inwater experiment illustrates that this technique is extremely desirable for collision resolution in underwater acoustic local area networks, and also for underwater autonomous vehicles with both sidescan sonar as well as acoustic telemetry links     

Acoustic inversion of bottom reflectivity and bottom sound-speedprofile

This paper applies a full-field technique to invert bottom sound profile and bottom reflectivity from simulated acoustic data in a shallow water environment. Bottom sound-speed profile and bottom reflectivity have been traditionally estimated using seismic reflection/refraction techniques when acoustic ray paths and travel time can be identified and measured from the data. However, in shallow water, the many multipaths due to bottom reflection/refraction make such identification and measurement rather difficult. A full-field inversion technique is presented here that uses a broad-band source and a vertical array for bottom sound-speed and reflectivity inversion. The technique is a modified matched field inversion technique referred to as matched beam processing. Matched beam processing uses conventional beamforming processing to transform the field data into the beam domain and correlate that with the replica field also in the beam domain. This allows the analysis to track the acoustic field as a function of incident/reflected angle and minimize contamination or mismatch due to sidelobe leakage     

海上浅地层剖面处理的关键去噪技术

在海上地球物理调查中,为了查明该海区的浅部地层结构和分布规律,浅地层剖面测量是一种不可缺少的重要的手段;然而,海上数据采集过程通常会受到各种因素干扰,导致获得的浅剖资料噪声严重。其主频虽然较高,但信噪比较低,以致于在原始剖面中无法有效地识别地层。以辽河三角洲资料为例,针对剖面上存在的各种噪声类型,提出一些用于浅地层剖面资料处理的关键技术,以提高原始资料信噪比及分辨率为目的,为海洋地质构造的解释提供良好的基础资料。