遗传算法在起伏地形下磁异常反演的应用

实际的地面磁法勘探往往是在山区进行,所测得的磁测结果也是沿地形起伏分布,这样往往会对磁异常曲线形态产生畸变,因此在起伏地形条件下,对磁测结果进行必要的反演,将会更明确地下目标地质体的位置与形态。本文首先模拟在水平条件下板状体的磁异常剖面曲线,检验算法的正确性,然后模拟在起伏地形下板状体的磁异常剖面曲线,并应用遗传算法对所得异常曲线进行反演并讨论其可行性,加入噪声并对其反演,讨论算法的抗干扰性,最后将其应用至实际找矿项目中。反演的结果表明,该方法在实际应用中具有一定参考作用。     

受控三轴应力-应变下沉积物声速与物理力学性质的关系

对南海某海域深度100～400 m的海底浅层（约2 m埋深范围）沉积物柱状样在接近海底水压力下进行三轴应变-声学同步测量,结果表明沉积物纵波声速有两个特征:（1）从应变过程开始到结束,沉积物纵波声速不断变化;（2）平均声速随着平均静弹性模量的增加,由大变小又由小变大,存在声速最小值。这些结果与海底浅表层沉积物的物理力学性质、围压、颗粒的结合状态改变有关。此外,沉积物动弹性模量和孔隙度呈良好的负相关性,这与孔隙度增大含水量增大有关;动弹性模量是静弹性模量的10～100倍,这主要与三轴应变试验的应变数量级与声波振动产生的应变数量级的差异大有关。采用本论文实验测量的数据分别建立了双复合参数-声速和孔隙度-声速经验公式,分析结果表明双复合参数-声速公式声速预报误差约是孔隙度-声速公式的1/4,表明双复合参数-声速公式更加有效。     

海底大地测量控制网研究进展综述

高精度的海底大地测量控制网是数字海洋和水下网络中心战的基础设施之一,而现阶段我国海底控制网的建设和研究几乎为空白。为自主建立我国高精度的海底大地测量控制网,本文借鉴发达国家的经验,结合国外海底控制网的发展与研究现状,系统介绍了GNSS/Acoustic系统的组成及发展;详细梳理了数据处理中的关键技术,分析了影响海底控制点精度的因素和控制点定位精度;结合我国现状,建议加紧开展我国海底控制网的建设与研究。     

A coupled atmospheric and topographic correction algorithm for remotely sensed satellite imagery over mountainous terrain

Radiometric correction is an important issue in the quantitative remote-sensing community. By integrating dark object subtraction (DOS)-based atmospheric correction with physics-based topographic correction, a coupled land surface reflectance retrieval algorithm (coupled atmospheric and topographic correction algorithm, named the CAT algorithm) for rugged mountainous regions is proposed. Terra MODIS-derived atmospheric characterization data (including aerosol optical depth, integrated precipitable water, surface pressure, and ozone concentration) are employed as inputs for the proposed algorithm. A physics-based path radiance estimation model is proposed and embedded in the CAT algorithm, and band-specific per-pixel path radiance values are calculated. After the CAT algorithm was performed, the correlation between reflectance and terrain was dramatically reduced, with correlation coefficients nearly equal zero, especially for the near infrared and short-wave infrared bands, meanwhile the image information content increased over 20%. To provide a comparison with previous studies, two commonly used methods in the literature (DOS + Cosine and DOS + C) were employed. The results of the comparison show that the proposed algorithm performed better in both atmospheric and topographic corrections without empirical regression.     

海底热液循环中矿物沉淀过程数值模拟

为了探索高渗透性洋壳中高温热液循环系统的形成机制,以数值模拟为手段研究热液循环中的矿物沉淀过程及其对洋壳渗透率的反馈.在热液对流-矿物反应模型中考虑了硬石膏、黄铁矿和黄铜矿的沉淀和溶解反应,基于矿物的溶度积计算矿物的沉淀/溶解量,并将其转换为渗透率的变化.结果显示,黄铁矿和黄铜矿分布于350~380℃等温线范围内,并随着热液温度升高而逐渐向海底推移.海水被加热及与热液混合过程中沉淀出硬石膏,在热液上升通道两侧形成低渗透性的烟囱状结构,降低了海水-热液混合程度从而使热液温度升高.高温热液通道建立后,便会有更多的金属物质随着高温热液被运输至浅层洋壳或海底.模拟结果为理解海底高温热液喷口的形成机制提供了借鉴.      

Scientific information model for deepsea mapping and sampling

The Vents Program of the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory is an interdisciplinary research initiative that brings together scientists from a wide range of disciplines, including geophysics, geology, physical oceanography, chemistry, and biology. Each discipline collects a variety of data types of varying structures and requiring intercomparison. The challenge of scientific information management is thus approached with a view of supporting data from multiple survey, mapping, and sampling tools and subject to multiple levels of interpretation. The ultimate objective is a system that integrates the functions of data storage, selective retrieval, display, and archiving. The results of our ongoing efforts in scientific information modeling and management have produced a relational database in which marine geological, geophysical, chemical, and biological observations can be accessed by any investigator.     

Naval Mine Impact Burial Prediction using Seafloor Database,Experiment, and GIS Technologies

The possibility of naval mines buried in the seafloor poses difficulties for navies concerned with port and seaway operations. To devise countermeasures, predictions of degrees of impact burial over wide areas of seabed must be made. Under ideal conditions, this is done with a knowledge of local seabed shear strengths, but in practice, such data are rarely available.

We describe an alternative prediction method. Probabilistic predictions of mine impact burial are made across areas of variable seafloor by combining data on sedimentary character directly with experimental impact burial results. The most useful seafloor characteristics are mud content and consolidation. The predictions are relatively accurate (SD 1–22%), and are computable in detail over wide geographic areas. They are of a form immediately useful for naval operations (including calculations of risk) and are easily displayed in geographic information systems (GIS). An example is shown for the northern Gulf of Mexico.     

Study of the sedimentation and self-weight consolidation behavior of seafloor sediments using a radioisotope densitometer

ABSTRACT

In this study, settling tests were conducted to investigate the sedimentation and self-weight consolidation behavior of seafloor sediments from Isahaya Bay, Ariake Sea, Japan. During the tests, the density variations with depth and time were measured by a gamma-ray transmission radioisotope densitometer. The test results show that the settling process of the seafloor sediments can be classified into the flocculation stage, settling stage, and consolidation stage. The settling rate of the seafloor sediments in the settling stage is dependent on the temperature and initial water content, while the settling rate in the consolidation stage is independent of the temperature and initial water content. The density profile changes from a constant density profile to a linear density profile when the sedimentation process transitions to the self-weight consolidation process. The relations between the void ratio (e) and effective vertical stress (p’) at very low pressures can be calculated from the measured density values, and this can be used for the analysis of the self-weight consolidation of seafloor sediments. For the seafloor sediments tested in this study, the undrained shear strength (s_u) values are almost the same when the density values are less than 1.14?g/cm³, and the s_u values increase linearly with an increase in density when the density values are in the range of 1.14–1.2?g/cm^3.     

地球韵律的时空表现及动力问题

文章介绍了大洋底１５６６Ｍａ以来六个时段增生构造的划分，前五个时段平均３０Ｍａ，具一定韵律性，以此与中国大陆１７５Ｍａ以来岩浆 构造活动的分段进行了比较，它们共同的韵律时段是（３０±８）Ｍａ。文中还介绍了一组全球地震活动的分幕性及其空间展布的有趣现象，包括低、中纬度与高纬度地震２０年左右的交替活动，南、北极区地震的交替活动，Ｍｓ≥８级大震呈现正交型与斜交型全球图像的分幕性交替活动，还有地球转速加速期和减速期地震发生地区的韵律性分布等。就上述中期和短期的地球韵律表现，进行了地球韵律判定的复杂性和动力学背景的讨论，强调了地球韵律的应用和地球本体研究的重要性。     

Pockmarks off Big Sur, California

A pockmark field was discovered during EM-300 multi-beam bathymetric surveys on the lower continental slope off the Big Sur coast of California. The field contains ∼1500 pockmarks which are between 130 and 260 m in diameter, and typically are 8-12 m deep located within a 560 km² area. To investigate the origin of these features, piston cores were collected from both the interior and the flanks of the pockmarks, and remotely operated vehicle observation (ROV) video and sampling transects were conducted which passed through 19 of the pockmarks. The water column within and above the pockmarks was sampled for methane concentration. Piston cores and ROV collected push cores show that the pockmark field is composed of monotonous fine silts and clays and the cores within the pockmarks are indistinguishable from those outside the pockmarks. No evidence for either sediment winnowing or diagenetic alteration suggestive of fluid venting was obtained. ¹⁴C measurements of the organic carbon in the sediments indicate continuous sedimentation throughout the time resolution of the radiocarbon technique (∼45?000 yr BP), with a sedimentation rate of ∼10 cm per 1000 yr both within and between the pockmarks. Concentrations of methane, dissolved inorganic carbon, sulfate, chloride, and ammonium in pore water extracted from within the cores are generally similar in composition to seawater and show little change with depth, suggesting low biogeochemical activity. These pore water chemical gradients indicate that neither significant accumulations of gas are likely to exist in the shallow subsurface (∼100 m) nor is active fluid advection occurring within the sampled sediments. Taken together the data indicate that these pockmarks are more than 45?000 yr old, are presently inactive, and contain no indications of earlier fluid or gas venting events.