连续小波变换识别位场场源法的噪声影响分析与尺度因子的选择

为提高连续小波变换识别位场场源准确度,研究噪声对场源识别结果的影响和尺度因子优选方法问题。根据连续小波变换识别位场场源的基本原理,用该方法对不同噪声水平的合成数据进行场源识别,分析噪声对于场源识别结果的影响,研究小波变换的尺度因子对噪声压制的效果,讨论连续小波变换进行场源识别时尺度因子的选取方法。理论模型和实测资料场源识别结果表明,噪声会降低连续小波变换场源识别结果的准确度,笔者提出的尺度因子优选方法能有效压制噪声干扰,提高场源识别结果的准确度。     

小波结合幂次变换方法在边界识别中的应用

在位场数据边界识别传统方法理论的基础上,前人研究了各种场源边界增强技术来提高信噪比和定位精度,但仍然存在受噪声影响大、场源边界不够收敛等问题。本文在传统边界识别方法的基础上进行改进,利用小波变换与传统方法相结合来增强对噪声的压制能力,并且提出了幂次变换法对识别出的边界进行有效收敛。将改进方法与传统方法应用于地质体的边界识别;同时选取3种传统数值计算方法,结合模型数据、四川盆地重力异常数据及朱日和地区磁异常数据进行对比分析。结果表明：小波结合幂次变换法能够有效识别出研究区域内地质体的边界,能很好地起到压制噪声的作用;并且识别出的边界收敛,提高了边界识别的精度,在边界识别中取得了良好的效果。     

缝合线的分形结构

在地层系统中，分形结构的识别日益广泛。在标度不变的沉积构造“泛监”之时，缝合是最具启发性的分形样式之一。对垂向剖面上的缝合线迹线曾做过标准傅立叶频谱分析，它的频谱具有１／ｆ分数噪声特征。     

利用偏振约束的能量比微地震自动识别方法

微地震监测是分析水力压裂注水前缘或对油藏进行动态监测的一种有效方法.由于持续监测数据量大,而且有效微地震事件的出现时间无法判定,人工拾取需要耗费大量人力与时间,需要利用计算机对有效事件进行自动拾取.笔者分析了井中微地震监测背景噪声以及某些相关噪声特点,以长短时窗能量比法为基础,结合偏振分析,设计利用偏振一能量比综合的方法来识别微地震有效事件,经实际资料验证该方法具有一定的可靠性.根据实际有效信号与噪声在多级检波器之间的出现规律利用多级间时差对识别结果进行约束来排除某些特殊噪声的影响.将这种方法应用于整套水力压裂微地震监测资料中,能够快速稳定的识别出大量微地震有效事件,有比较好的应用效果.     

消除噪声的RNF图像融合算法

在多光谱遥感图像中有时也会存在较严重的随机点噪声的干扰，这种随机点噪声严重影响了地物光谱特征提取和识别的精度，降低了各种遥感定量分析方法技术的有效性。常用的遥感图像随机噪声消除或压抑方法是Fourier变换频率域方法和采用平滑模板对图像进行卷积处理的空间域方法，但它们往往会损失图像信息。文章探讨了消除或压抑噪声的图像融合方法，即RNF融合法。RNF融合算法先对参与融合的多光谱图像进行低通滤波，对全色波段进行高通滤波。然后将滤波后的全色波段与多光谱图像用HSI变换法进行融合，融合后的图像消除了噪声。     

水文序列小波分析中分解层数选择方法

小波分解层数的合理选择是水文序列小波分析结果的重要影响因素。在详细分析和定量描述不同类型噪声的能量分布规律的基础上,依据水文序列中确定成分和噪声成分的能量分布规律的差异,提出了一个小波分解层数选择方法。通过对不同类型模拟序列和不同特性实测水文序列进行分析,验证了所提方法的有效性和实用性。结果表明:序列组成、噪声含量等因素对小波分解层数的选择结果有较大影响,但噪声类型对小波分解层数选择结果影响较小;应用该方法确定小波分解层数的同时,还可以有效地识别和区分各层上是确定成分或是噪声成分,进而可为序列模拟预测提供依据。由于所提方法基于水文序列不同成分变化特性的差异建立,因此有较好的物理依据且分析结果合理可靠。     

柴达木盆地南缘玛兴大湾地区典型岩浆岩岩性识别研究

本文运用ASTER多光谱遥感数据识别柴达木南缘玛兴大湾地区典型岩浆岩的岩性信息,分别采用光谱分析法和最小噪声变换法进行试验,可有效地识别与提取出研究区内的典型岩浆岩岩性信息;经已知地质资料和野外查证资料分析证明,用上述方法提取岩性信息的结果可靠,能为岩性填图及矿床勘查工作提供参考。     

小波分析在天然伽玛测井地质解释中的应用

在分析天然伽玛测井数据的信息特点和小波多分辨率分析原理的基础上,用小波多分辨率分析天然伽玛测井数据,消除其中的统计涨落等噪声干扰及提取天然伽玛放射性强度在不同沉积岩地层中分界标志特征和不同岩性中的变化特征,以提高应用天然伽玛测井资料进行地层划分及岩性识别的准确性和有效性.     

重磁数据在东海陆架盆地构造格架划分中的应用

针对现有重磁构造识别深部地质体分辨率低的情况,提出改进局部相位边界识别技术,采用不同阶水平导数的比值函数有效地均衡不同深度构造的响应,提高了对深部地质体的分辨能力。理论模型试验表明改进局部相位边界识别技术能更加清晰和准确地识别地质体边界,且受噪声干扰较小。利用改进局部相位边界识别技术对东海陆架盆地重磁数据进行构造识别,并比照欧拉反褶积结果进行断裂划分,结合东海基底反演结果和地质资料给定东海陆架盆地的边界和主干构造格架。     

基于混合滤波的遥感图像去噪

遥感图像在生成、传输和转化过程中往往受到各种噪声的干扰,影响了图像本身的清晰度,降低了视觉效果,不利于真实信息的提取.研究目的是对高分辨率遥感图像进行预处理,以提高信息识别精度.研究方法是噪声检测结合混合滤波的方法,该方法基于均值滤波和中值滤波的互补性,首先对图像每一个像素点进行噪声检测,把受高斯噪声污染和受椒盐噪声污染的像素点区分开,然后分别对受高斯噪声污染和受椒盐噪声污染的像素点进行处理.与其他滤波算法进行比较的结果表明,噪声检测结合混合滤波方法能够有效去除椒盐噪声和高斯噪声,保留图像的纹理信息,提高图像的清晰度.     

Influence of sodium silicate addition on the adsorption of oleic acid by fluorite,calcite and barite

A study has been made of the adsorption of sodium silicate by calcite, fluorite and barite and the effect that this adsorption has on the flotation of these minerals with oleic acid. The results show that sodium silicate depresses these minerals by preventing oleate species from reacting with surface sites. This effect is independent of the total silica concentration. Aged sodium silicate solutions do not produce markedly different results to those obtained with fresh solutions.The concentration of the sodium silicate solutions was generally such that the total silica concentration was below that in equilibrium with amorphous silica. Under these conditions the solutions contained no polymeric silica species and the mechanism of silica adsorption can be generally attributed to interactions of monosilicate ion and monosilicic acid with surface sites.     

Biological uptake and accumulation of silica on the Amazon continental shelf

Water column and seabed samples were obtained from 92 stations on the Amazon continental shelf during October of 1979. Uptake of silica near and southeast of the river mouth began at a salinity of 8%. and accounted for 17% of the riverine silica flux to this region. Uptake northwest of the river mouth began at a salinity of 20%. and resulted in 33% removal of the riverine silica flux. Examination of filtered suspended solids revealed abundant diatoms in the surface waters, including Coscinodiscus. Skeletonema, Synedra. and Thalassiosira. The biological uptake of silica appears to be dependent on three factors: turbidity, turbulence, and nutrient availability. There was no evidence of abiological removal of silica in the Amazon estuary. 75 to 88% of the silica removed from surface waters by diatoms dissolves prior to accumulation in the seabed. Based on the mean biogenic silica content of shelf sediment (0.25%) and estimates of rates of sediment accumulation, the biogenic silica accumulation rate on the shelf is 2 × 10¹² g/yr, which represents only 4% of the dissolved silica supplied by the Amazon River. Biological uptake of silica in estuarine surface waters may not accurately reflect permanent removal of biogenic silica to the seabed because of dissolution which occurs in bottom waters and near the sediment-water interface.     

The lack of inorganic removal of dissolved silica during river-ocean mixing

The significance of the inorganic removal of dissolved silica from estuarine zones was investigated at three river mouths: the Orinoco, the Savannah and the Mississippi. Particular attention was given to the Mississippi river plume, where extensive inorganic silica uptake had been reported. Mixing curves and laboratory dilution experiments provided little evidence that the phenomenon was widespread. Because of an uncertain fresh water tie point, some inorganic uptake could not be completely ruled out for the Orinoco, but, in the plumes of the Savannah and Mississippi rivers, no inorganic silica removal was indicated. In contrast to published experiments on river sediments, laboratory dilution studies on suspended matter from the Mississippi river showed release of dissolved silica instead of uptake.     

利用粉煤灰制备多孔氧化硅的实验

利用相分离原理,以粉煤灰经硅铝分离后所得的硅酸凝胶为原料,选用聚乙烯醇为造孔剂,硝酸为催化剂,成功地制备了多孔氧化硅。实验结果表明:制备的多孔氧化硅的孔道发育良好,含有三级孔道。扫描电镜分析显示:大孔孔径为1～2 μm,比表面积为12.03 m²/g,这与实际应用的硅藻土助滤剂制品大致相当。对实验制品在啤酒液中的稳定性实验结果显示:多孔氧化硅制品在浸泡于啤酒过程中几乎没有Ca²⁺、Fe³⁺离子溶出,浸泡后的啤酒液的pH值基本不变。上述结果表明:实验制备的多孔氧化硅制品作为硅藻土助滤剂的替代品具有良好的实际应用前景。     

Silica depleted melting of pelites. Petrogenetic grid and application to the Susqueda Aureole, Spain

Metapelitic rocks in the low pressure contact metamorphic aureole around the Susqueda igneous complex, Spain show a number of features that make them an ideal testing ground for the modelling of silica‐undersaturated melting. Rocks in the aureole experienced localized depletion in silica by the segregation of quartz veins during a pre‐anatectic, regional cordierite‐andalusite grade metamorphic event. These rocks were then intruded by gabbroic to dioritic rocks of the Susqueda igneous complex that formed a migmatitic contact metamorphic aureole in the country rocks. This migmatisation event caused quartz‐saturated hornfels and restite formation in rocks that had experienced no quartz vein segregation in the previous regional metamorphic event, but silica‐undersaturated melting in those rocks that were previously depleted in silica. Silica‐undersaturated melting is investigated using a new petrogenetic P–T projection and equilibrium pseudosections calculated in the KFMASH and NCKFMASH systems, respectively. The grid considers quartz absent equilibria and a range of phases that form typically in silica‐undersaturated bulk compositions, for example corundum. It is shown that the quartz‐rich precursors in the Susqueda contact aureole produced about 10% melt during contact metamorphism. However, most of this melt was extracted leaving behind rocks with restitic bulk compositions and minor leucosome segregation. It is suggested that the melt mixed with the host igneous rocks causing an apparent magmatic zoning from diorite in the centre of the complex to tonalite at the margins. In contrast, the quartz‐poor precursors (from which the quartz veins segregated) melted in the silica‐undersaturated field producing a range of assemblages including peritectic corundum and spinel. Melting of the silica‐undersaturated rocks produced only negligible melt and no subsequent melt loss.     

Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub‐aquatic opaline stromatolite formation (Terceira,Azores)

Silica stromatolites occur in a number of modern hydrothermal environments, but their formation in caves is very rare. The silica stromatolitic speleothems of the Branca Opala cave (Terceira Island, Azores), however, provide an excellent opportunity for their study. These formations may be analogous to ancient silica stromatolites seen around the world. Petrographic, mineralogical and geochemical analyses were undertaken on the silica speleothems of the above cave, and on the silica‐tufa deposits outside it, with the aim of understanding their genesis. The possible hydrothermal origin of their silica is discussed. X‐ray diffraction analyses showed opal‐A to be the sole silica phase. Negligible ordering of this opal‐A showed ageing to be insignificant, as expected for recent silica deposits. Most of the silica speleothems examined were definable as sub‐aquatic opaline stromatolites that are not currently growing. Optical microscopy clearly revealed a lower microlaminated, an intermediate and an upper microlaminated zone within the stromatolites. Stromatolite types (I, II and III) were classified with respect to their internal structure and distribution throughout the cave. Scanning electron microscopy showed silicified bacterial filaments within the stromatolites, the silicified plant remains and the silica‐tufa deposits. Bacteria therefore played a major role in the precipitation of the opal‐A. Plasma emission/mass spectrometry showed major, minor and rare earth elements to be present in only small quantities. The rare earth elements were mainly hosted within volcanic grains. Rapid silica precipitation from highly super‐saturated water would explain the intense silicification of the plant remains found inside and outside the cave. The opaline stromatolites, the silica‐tufa deposits and the above‐mentioned intense general silicification suggest a local hydrothermal source for the silica. Indeed, these deposits strongly resemble plant‐rich silica sinter associated with low‐temperature hot spring deposits that include bacterial filaments. However, no geochemical signals that might indicate a hydrothermal origin could be found.     

Size distribution of quartz in mudrocks

Sixteen penecontemporaneously deposited mudrock-sandstone pairs ranging in age from Devonian to Cretaceous were treated chemically to isolate the quartz and chert fraction from the other constituents of the rocks. The amount of crystalline silica was determined from the chemical treatments; its size distribution was determined using a combination of normal and Micro Mesh sieving and settling tube analysis; the crystalline silica coarser than 10 μu was examined petrographically to determine the amount of chert. Percentages of crystalline silica in the mudrocks range from 6·7 to 46·7 % and average 27·6 (σ= 10·7). Mean grain size ranges from 4·4 φ to 7·3 φ and averages 6·1 φ. The crystalline silica fraction is a poorly sorted medium to fine silt consisting of one-eighth sand, six-eighths silt, and one-eighth clay size sediment. Percentage of crystalline silica and mean size of crystalline silica in the thirty-two mudrocks and sandstones are positively correlated; r= 0·685, which is significant at the 99 % level. The best fit linear regression line is: Y= 102·7–11·3X. Extrapolation of the regression line indicates that, on the average, crystalline silica is lacking in mudrocks in grain sizes finer than 9·1 φ (1·μm), a result consistent with observations by clay mineralogists. The crystalline silica fraction of both the mudrocks and associated sandstones averages 4% chert in the >10 μm portion. There is no correlation between the mean grain size of the crystalline silica and the percentage of chert in it.     

Geostatistical modelling of lateritic bauxite orebodies in Surinam: effect of the vertical dimension

Lateritic bauxite deposits in Surinam have until now been modelled in two dimensions. The samples collected by auger drill are composited into 1 m (3 ft) intervals and the accumulated grade per hole used as the input for statistical and geostatistical studies. The aim of the study presented in this paper is to quantify the information lost by working with accumulated grades. In other words, the third dimension is taken into account, by considering successive slices with a thickness of 1 m. The composition of the bauxite orebody is characterised by the loss on ignition (LOI), silica, titanium oxide, iron oxide and aluminium oxide contents.The average grade of silica increases significantly with depth, whereas the decrease in the average LOI is only minor. The statistical study indicates two populations for silica and LOI, at least for the fourth slice (at 3–4 m from the top of the orebody) and deeper. For iron oxide a significant decrease with depth is observed, but for each slice only one population could be distinguished. For titanium and aluminium oxide no significant variation with depth and no multi-populations are observed. All these observations are linked to the weathering process, which is the process of genesis of bauxite. The higher the samples are in the profile, the more intense the weathering has been, as indicated by the leaching of silica. These observations confirm that a horizontal zoning is present.For all five parameters studied, a spatial correlation in the horizontal plane is noted for the successive slices. The range of this correlation is on average 200–250 m, and a relative nugget of 35–80% is calculated depending on the parameter and the depth position.The study presented shows clearly that there is a variation with depth. By considering accumulated values, some of this information is lost. For example, for the accumulations of silica and iron oxide no spatial correlation is observed, whereas for the individual slices a distinct spatial correlation is present.     

The Ge/Si ratio as a tool to recognize biogenic silica in chert

Germanium and silicon, dissolved in seawater, are considered to be incorporated into biogenic opal with no or little fractionation, which permitted to use diatoms as reliable recorders of seawater Ge/Si. Does some fractionation occur during diagenesis, preventing the use of Ge/Si in ancient sediments? We examined the Ge/Si ratio of fossil sponges and flint nodules of the Cretaceous Chalk Formation of northern France. Though disputed, silica in this formation is considered to originate from sponges. No fractionation is observed between sponges and diagenetic flints, which allows us to observe whether Ge/Si bears a biogenic or detrital signature. We may thus confirm that sponges were the main silica supplier during the chalk deposition. The Ge/Si ratio may be used to identify a biogenic signature in cherts where the origin of silica is dubious.     

Silicification in the Belt Supergroup (Mesoproterozoic), Glacier National Park, Montana, USA

Nodular cherts can provide a window on the original sediment composition, diagenetic history and biota of their host rock because of their low susceptibility to further diagenetic alteration. The majority of Phanerozoic cherts formed by the intraformational redistribution of biogenic silica, particularly siliceous sponge spicules, radiolarian tests and diatom frustules. In the absence of a biogenic silica source, Precambrian cherts necessarily had to have had a different origin than Phanerozoic cherts. The Mesoproterozoic Belt Supergroup in Glacier National Park contains a variety of chert types, including silicified oolites and stromatolites, which have similar microtextures and paragenesis to Phanerozoic cherts, despite their different origins. Much of the silicification in the Belt Supergroup occurred after the onset of intergranular compaction, but before the main episode of dolomitization. The Belt Supergroup cherts probably had an opal-CT precursor, in the same manner as many Phanerozoic cherts. Although it is likely that Precambrian seas had higher silica concentrations than at present because of the absence of silica-secreting organisms, no evidence was observed that would suggest that high dissolved silica concentrations in the Belt sea had a significant widespread effect on silicification. The rarity of microfossils in Belt Supergroup cherts indicates that early silicification, if it occurred, was exceptional and restricted to localized environments. The similarity of microtextures in cherts of different ages is evidence that the silicification process is largely controlled by host carbonate composition and dissolved silica concentration during diagenesis, regardless of the source of silica.