Optimum parameter selection in offset-dependent predictive deconvolution: testing on multichannel marine seismic data

Marine Geophysical Research - Predictive deconvolution is an effective way to suppress multiple reflections, especially short path multiples, in seismic data. However, the effectiveness of the...     

Dereverberation of marine reflection seismic data by a spatial combination of predictive deconvolution and velocity filtering

Contamination of seismic reflection records at early times by first-order water reverberations can be especially severe during survey operations over hard and flat sea floors on the continental shelf or in lake environments. A new dereverberation scheme based on two classical techniques — predictive deconvolution and velocity filtering — has been developed to address this problem. The techniques are combined spatially to take advantage of their complementary offset- and time-dependent properties. Stage I of the scheme consists of applying predictive deconvolution at short offset. The data are previously conditioned by a normal moveout correction with the water velocity which restores the periodicity of the reverberations in the offset-time plane and enhances the performance of deconvolution. Stage II of the scheme involves velocity filtering in the common-midpoint domain which is particularly effective at long offset where the moveout difference between primary reflections and reverberations is largest. The dereverberation scheme is well suited for the initial processing of large volumes of data due to the general availability of cost-effective deconvolution and velocity filtering algorithms in seismic processing software packages. Practical implementation issues are illustrated by a field example from the GLIMPCE survey in Lake Superior.Lithoprobe Publication No. 475.     

Correction for water depth variations of marine crustal reflection seismic data using refraction statics

Water depth variations in marine reflection seismic profiling cause velocity push-down and, in regions of rapid fluctuations of the water-bottom slope, stack degradation. Static corrections are a very satisfactory and practical solution to these problems under typical survey conditions with water depths not exceeding a few hundred metres and relatively hard water bottoms. Static time shifts are best derived from a refraction analysis of first arrivals rather than from fathometer data, especially over underwater valleys where unconsolidated sediment of velocity close to that of water has been deposited unconformably onto the underlying lithified rocks. These points are illustrated by a field example from the GLIMPCE survey in Lake Superior. The availability of computer-effective algorithms such as the generalized linear inversion method allows the implementation of refraction statics during the initial processing of regional marine crustal surveys.LITHOPROBE Publication No. 263.     

Behavior of marine pipelines under seismic faults

A new study investigates an unburied offshore “snaked” pipeline behavior under various types of seismic faults. The snaking of the pipeline is caused by the thermal/pressure expansion and soil friction. The snaking takes place at a certain distance from the pipeline's unrestrained end and gradually increases towards the restraint. It is shown that longitudinal seismic faults have less effect on a straight pipeline than a snaked pipeline. The new seismic analysis demonstrates that an increase of ground displacement causes a very small change in bending and longitudinal stresses. The new approach results in a safe, subsea pipeline construction and operation with a significant cost reduction.     

Fast static correction methods for high-frequency multichannel marine seismic reflection data: A high-resolution seismic study of channel-levee systems on the Bengal Fan

Very high-frequency marine multichannel seismic reflection data generated by small-volume air- or waterguns allow detailed, high-resolution studies of sedimentary structures of the order of one to few metres wavelength. The high-frequency content, however, requires (1) a very exact knowledge of the source and receiver positions, and (2) the development of data processing methods which take this exact geometry into account. Static corrections are crucial for the quality of very high-frequency stacked data because static shifts caused by variations of the source and streamer depths are of the order of half to one dominant wavelength, so that they can lead to destructive interference during stacking of CDP sorted traces. As common surface-consistent residual static correction methods developed for land seismic data require fixed shot and receiver locations two simple and fast techniques have been developed for marine seismic data with moving sources and receivers to correct such static shifts. The first method – called CDP static correction method – is based on a simultaneous recording of Parasound sediment echosounder and multichannel seismic reflection data. It compares the depth information derived from the first arrivals of both data sets to calculate static correction time shifts for each seismic channel relative to the Parasound water depths. The second method – called average static correction method – utilises the fact that the streamer depth is mainly controlled by bird units, which keep the streamer in a predefined depth at certain increments but do not prevent the streamer from being slightly buoyant in-between. In case of calm weather conditions these streamer bendings mainly contribute to the overall static time shifts, whereas depth variations of the source are negligible. Hence, mean static correction time shifts are calculated for each channel by averaging the depth values determined at each geophone group position for several subsequent shots. Application of both methods to data of a high-resolution seismic survey of channel-levee systems on the Bengal Fan shows that the quality of the stacked section can be improved significantly compared to stacking results achieved without preceding static corrections. The optimised records show sedimentary features in great detail, that are not visible without static corrections. Limitations only result from the sea floor topography. The CDP static correction method generally provides more coherent reflections than the average static correction method but can only be applied in areas with rather flat sea floor, where no diffraction hyperbolae occur. In contrast, the average static correction method can also be used in regions with rough morphology, but the coherency of reflections is slightly reduced compared to the results of the CDP static correction method.     

Signal enhancement and multiple suppression using Radon transform: an application to marine multichannel seismic data

Radon filters are often used for removal of multiple reflections from normal move-out-corrected seismic reflection data. In the conventional Radon transform, integration surfaces are hyperbolic rather than linear. This specific hyperbolic surface is equivalent to a parabola in terms of computational expense, but more accurately distinguishes multiples from primary reflections. The forward transform separates seismic arrivals by their differences in travel time move-out. Multiples can be suppressed by an inverse transform of the seismic data. Examples show that multiples are effectively attenuated in pre-stack and stacked seismograms. Based on the parabolic Radon transform, a new method is utilized for missing offset restoration, resampling and regularization of pre-stack individual common depth point (CDP) gathers. The method is also valid for resampling spatially aliased seismic data. Restoration of missing offsets and trace interpolation is an interesting and important problem in seismic data processing. Here we present an application of Radon transform on a multichannel seismic data set from the western continental margin of India (WCMI), which shows remarkable signal enhancement.     

Methodology for wide-angle seismic modeling of marine gas hydrate deposits

A wide angle seismic modeling methodology was developed for the purpose of studying marine gas hydrate deposits. The software for seismic modeling was selected on the basis of comparative analysis and testing of different computer programs. Five averaged prognostic two-dimensional models were developed. These models include the gas hydrate zone, the free gas zone, and the basement. The prognostic models suggested represent the structure of gas hydrate deposits for various regions of the World Ocean. Wave field calculations were made for various positions of ocean bottom seismometers with respect to the gas hydrate zone using the seismic tomography technique. Numerical experiments showed significant anomalies of the kinematical and dynamical characteristics of the refracted and wide-angle reflected waves. These anomalies are related to the gas hydrate and the free gas zones and to a possible channel of hydrocarbon supply.     

High-resolution seismic reflection surveying of shallow marine and estuarine environments

High-frequency seismic reflection profiling is a well-established and often used technique in marine investigations. Traditionally seismic data are viewed as two-dimensional time sections. Given closely spaced profile lines, it is possible to produce posted two-way travel time maps of sub-surface reflectors which, when plotted as isometric displays, clearly show the three-dimensional spatial morphology of the sub-surface topography. With borehole control, such information can be used to provide a series of images which indicate temporal as well as spatial relationships of sub-surface reflectors. With the high-resolution afforded by high-frequency methods, detailed information on palaeo-environments can be reconstructed. Using the geophysical database as a basic framework, other aspects of the same environment can be examined in considerable detail. To demonstrate the effectiveness of these procedures, examples will be given from Plymouth Sound where a series of nested buried rock valleys has been mapped in detail from Sparker and Boomer surveys which have been interpreted in the light of newly-acquired borehole information. Isometric plots of the various sub-surface interfaces show how the channels have developed as sea level has risen over the last ca. 10,000 years. Different sedimentological facies can be resolved within the channel system thus providing information about the processes involved in their formation. Methods of improving the resolution and subsequent geological interpretation of high-resolution seismic reflection surveys are being developed for shallow marine and estuarine environments such as those found in Plymouth Sound.     

海洋地震垂直缆在自由状态下的照明情况

海洋垂直缆地震数据采集具有高分辨率、高精度真三维成像等特点。作为未来海洋立体观测系统的重要组成部分,有必要全面分析海洋垂直缆观测系统中影响照明的因素,并优选出最佳设计方案。在垂直缆存在倾角的情况下,分析激发点密度、接收点密度、离底高度、倾角变化以及地层倾斜对目标层照明情况的影响,发现激发点密度与接收点密度直接影响目标层的总覆盖次数,海洋垂直缆的倾斜会影响低覆盖带的位置,海底坡度以及目标层的倾角使得照明聚光范围产生移动,地下隆起的目标层覆盖范围更大,照明强度更优。设计观测系统时,不仅考虑上述影响因素,而且垂直缆布设的位置也应当根据地层倾角以及垂直缆倾角,避开低覆盖带而选择高覆盖区域。     

An overview of statistical methods applied to CPR data

Since the beginning of the Continuous Plankton Recorder (CPR) survey in 1931, information on the abundance of a large number of plankton species or taxa has been obtained on a monthly basis in the northern North Atlantic. The many different ecological issues in which the survey has been involved have led to the application of a range of statistical methods. In this paper, we review some of the methods applied to the CPR data by presenting new and up-to-date analyses. Special attention is devoted to multivariate analysis, which has been used extensively to extract information from the CPR database. Results obtained from recently applied geostatistical methods on CPR data are then considered. An example of a time series decomposition by the use of Eigenvector filtering is presented to illustrate time-series analysis.     

A protocol for classifying ecologically relevant marine zones,a statistical approach

Mapping ecologically relevant zones in the marine environment has become increasingly important. Biological data are however often scarce and alternatives are being sought in optimal classifications of abiotic variables. The concept of ‘marine landscapes’ is based on a hierarchical classification of geological, hydrographic and other physical data. This approach is however subject to many assumptions and subjective decisions.     

基于GIS的海洋地震数据管理系统的设计与实现

基于大型Oracle数据库管理系统和先进的空间数据引擎SDE技术,将SEG-Y格式海洋地震数据与地理信息系统相结合,并按照“航次—测线—点”的数据组织结构设计了海洋地震数据库.论文首先总结了当前流行的地震数据组织和访问方式,然后阐述了地震数据管理系统的设计方案,最后介绍了数据查询、数据库管理、SEG-Y地震数据查看和地...     

海洋多道地震拖缆数据采集包设计

针对海洋地震信号幅度小、动态范围大、噪声干扰强等特点,设计了基于高精度32位Δ-Σ(Sigma-Delta)模数转换器(ADC)的海洋多道地震拖缆四通道采集包。该地震信号采集包以STM32L432为核心,使用SPI总线控制4片32位模数转换器完成地震信号采集,采用九轴姿态传感器实时监测拖缆姿态,通过RS485接口将地震数据和姿态数据上传到数传包。测试表明:该装置自噪声小、动态范围大、功耗小、运行可靠,对海洋地震勘探高精度信号采集研究具有借鉴意义。     

Some statistical methods of the objective classification of oceanographic data

Algorithms for the compression and objective classification of low-volume samplings according to the test of their belonging to different statistical populations are given. Samplings are discriminated by thex ² test. The distributions of the temperature patch horizontal scales in the upper ocean are analysed. It is shown that optimum empirical thresholds exist when the abstract classification mechanism goes over to the objective natural classification.Translated by Mikhail M. Trufanov.     

基于SPSS的数理统计方法在海洋重金属环境背景值计算中的应用

讨论并计算了海水中重金属的含量值域.基于SPSS的主成分分析方法,将Cu,Pb,Zn,Cr,Hg,As,Cd7类重金属构成3个主成分,再通过主成分权重值作图划分调查海域的环境统计单元.对重金属进行异常值判定和分布类型检验,最终得到重金属的环境背景值.     

基于海洋安全的大气波导观测方法研究

海上船舶一旦遇到大气波导,可使船载电子信息系统之间的短波通信距离增大数倍,同时通信距离范围内的部分区域会出现电磁盲区.本文围绕海洋安全保障需求,开展了大气波导协同观测技术研究,阐述了海上大气波导对超视距传输与探测的重要性.通过对大气波导的形成机制和影响机理进行研究,系统化概述了蒸发波导、表面波导和抬升波导的观测原理及常...     

海洋硫酸多糖几种脱硫方法的比较研究

以κ-卡拉胶(硫酸基含量25.1％,分子质量83.1 kD)为原料,研究了二甲基亚砜-甲醇法(DMSO法)、三甲基氯硅烷法(CTMS法)以及苯并四甲酸-三氧化二锑法(PMA法)对其脱硫后多糖样品的得率、硫酸基含量及分子质量的影响.结果表明,κ-卡拉胶经三种方法脱硫后,样品得率分别为45.3％、50.6％和62.0％,脱硫率分别为42.2％、48.6％和82.8％,分子质量分别为15.7、22.3和4.75 kD.通过红外光谱和硫酸基含量分析表明,PMA法脱硫效果优于DMSO和CTMS法.PMA法不仅对κ-卡拉胶有效,而且适合于l-卡拉胶、λ-卡拉胶和岩藻聚糖硫酸酯的脱硫.     

海洋沉积物中多元素分析测定方法

介绍了海洋沉积物消化及多元素分析的测定方法。分析测定过程中 ,应选用国家标准溶液。标准溶液的蒸发次数、加酸量、稀释倍数等对样品测定结果的准确性均有一定影响。消化过程中 ,过多的蒸发次数对微量元素 Cr、V的测定结果有明显影响 ,蒸发的次数越多 ,元素的损失量越大 ,因此 ,为了获得更准确的测定结果 ,应尽可能减少蒸发次数 ,并减少加酸量 ;测定常量元素时 ,样品较大的稀释倍数使获得数据的可靠性增大 ,通常 0 .2 5 g样品应稀释至 5 0m L,0 .5 g样品应稀释至 1 0 0 m L。