Monte Carlo Radiative Transfer Modeling of Lightning Observed in Galileo Images of Jupiter   总被引：1，自引：0，他引：1  

U.A. DyudinaA.P. Ingersoll  A.R. VasavadaS.P. Ewald  the Galileo SSI Team 《Icarus》2002,160(2):336-349

We study lightning on Jupiter and the clouds illuminated by the lightning using images taken by the Galileo orbiter. The Galileo images have a resolution of ∼25 km/pixel and are able to resolve the shape of single lightning spots, which have half widths (radii) at half the maximum intensity in the range 45-80 km. We compare the shape and width of lightning flashes in the images with simulated flashes produced by our 3D Monte Carlo light-scattering model.The model calculates Monte Carlo scattering of photons in a 3D opacity distribution. During each scattering event, light is partially absorbed. The new direction of the photon after scattering is chosen according to a Henyey-Greenstein phase function. An image from each direction is produced by accumulating photons emerging from the cloud in a small range (bins) of emission angles. The light source is modeled either as a point or a vertical line.A plane-parallel cloud layer does not always fit the data. In some cases the cloud over the light source appears to resemble cumulus clouds on Earth. Lightning is estimated to occur at least as deep as the bottom of the expected water cloud. For the six flashes studied, we find that the clouds above the lightning are optically thick (τ>5). Jovian flashes are more regular and circular than the largest terrestrial flashes observed from space. On Jupiter there is nothing equivalent to the 30-40-km horizontal flashes that are seen on Earth.  相似文献   

Magnetic properties of soils from sites with different geological and environmental settings   总被引：7，自引：0，他引：7  

Hana Fialov  Günter Maier  Eduard Petrovský  Ale&#x; Kapi ka  Tetyana Boyko  Robert Scholger  MAGPROX Team 《Journal of Applied Geophysics》2006,59(4):273-283

Measurements of magnetic susceptibility of soils, reflecting magnetic enhancement of topsoils due to atmospherically deposited magnetic particles of industrial origin, are used recently in studies dealing with outlining polluted areas, as well as with approximate determination of soil contamination with heavy metals. One of the natural limitations of this method is magnetic enhancement of soils caused by weathering magnetically rich parent rock material. In this study we compare magnetic properties of soils from regions with different geological and environmental settings. Four areas in the Czech Republic and Austria were investigated, representing both magnetically rich and poor geology, as well as point-like and diffuse pollution sources. Topsoil and subsoil samples were investigated and the effect of geology and pollution was examined. Magnetic data including mass and volume magnetic susceptibility, frequency-dependent susceptibility, and main magnetic characteristics such as coercivity (Hc and Hcr) and magnetization (Ms and Mrs) parameters are compared with heavy metal contents. The aim of the paper is to assess the applicability of soil magnetometry under different geological-environmental conditions in terms of magnetic discrimination of dominant lithogenic/anthropogenic contributions to soil magnetic signature. Our results suggest that lithology represents the primary effect on soil magnetic properties. However, in case of significant atmospheric deposition of anthropogenic particles, this contribution can be clearly recognized, independent of the type of pollution source (point-like or diffuse), and discriminated from the lithogenic one. Different soil types apparently play no role. Possible effects of climate were not investigated in this study.  相似文献   

陕西凤县八方山-二里河（铜）铅锌矿床地质特征及成矿模式     

陈二虎张新胜  高卫宏 《西北地质》2007,40(B07):13-17

在综合分析凤-太矿集区成矿构造特征的基础上，依据以往总结的凤．太矿田铅锌、金矿聚矿构造模式，通过对八方山-二里河铅锌矿床地质特征的分析，总结了找矿标志，初步认为八方山-二里河（铜）铅锌矿床的成矿模式为：“前泥盆纪海底热水喷流沉积一印支-燕山期构造改造型”铅锌矿床。认为成矿物质来源于基底，后期的构造-岩浆改造使基底成矿元素活化，沿同生断裂迁移、改造，最后在泥盆系中形成的扩容性构造部位富集成矿。提出了下一步扩大找矿的方向和建议。  相似文献   

陆相沉积的天文地层研究方法简介——以井下地层为例   总被引：2，自引：5，他引：2  

XU Dao-yi )  ZHANG Hai-feng )  HAN Yan-ben )  YIN Zhi-qiang )  LI Bao-li )  YAO Yi-min ) ) Institute of Geology  China Earthquake Administration  Beijing    ) Geological Scientific Research Institute of Shengli Oilfield Company  SINOPEC  Dongying    ) National Astronomical Observatories  Chinese Academy of Sciences  Beijing 《地层学杂志》2007,(Z2)

通过对我国大陆三十余口井的测井资料研究成果,归纳出对陆相地层进行天文地层研究的方法。介绍了所用的新的天文周期理论值、测井资料的选取及预处理方法,重点说明谱分析的数据点数的选定、不同参数(自然伽玛、自然电位和岩屑)的测井资料谱分析结果的对比,以实例说明如何选定主要优势旋回和AR值,以及FIR数字滤波器的基本性质和数字滤波结果,小波分析的特点和通过小波图进行调频的方法,并介绍了地层单位的延续时间计算和年龄确定方法。  相似文献   

东营凹陷牛庄地区沙三段层序地层分析     

WANG Wei-qing ))  LIU Ning )  TIAN Fang ) ) Guangzhou Institute of Geochemistry  Chinese Academy of Sciences  Guangzhou    ) Geological Scientific Research Institute of Shengli Oilfield Company  SINOPEC  Dongying 《地层学杂志》2007,(Z2)

山东济阳坳陷东营凹陷牛庄地区沙三段层序地层分析是在三级层序划分的基础上,通过对沉积体系发育特征和气候旋回单元的识别和解剖,建立了高精度层序地层单元的基本构型。气候旋回包含了从干旱枯水期到潮湿湖泛期的完整过程,沉积响应为受湖平面变化、沉积物供给等因素控制的多种方式叠置的湖底扇和前积体等,多期气候旋回叠合构成了湖泊层序的基本面貌。通过气候旋回的识别,可以对不同级别层序间的包含关系,以及高精度层序的内部构成进行分析和讨论。  相似文献   

东营凹陷古近系层序地层对成岩规律的控制作用   总被引：2，自引：0，他引：2  

ZHANG Shou-peng ))  LIU Cheng-dong ) )Basin  Reservoir Research Center  China University of Petroleum  Beijing    )Geological Scientific Research Institute of Shengli Oilfield Company  SINOPEC  Dongying    ) Ministry of Education Key Laboratory of Nuclear Resources  Environment  East China University of Technology  Nanchang 《地层学杂志》2007,(Z2)

东营凹陷古近系发育了沙四段底界面(T7)、沙四段与沙三段分界面(T’6)及沙二下亚段顶界面(T’2)等3个二级层序界面。根据对储集层成岩作用的深入研究发现,原有的埋藏成岩作用序列不仅受深度的影响,而且受此层序地层所控制,在层序界面附近和层序体内部存在一定的规律性。据此确定了层序界面附近发育的淋滤、溶解成岩相带和层序体内部发育的黏土矿物转换和化学胶结成岩相带。认识到层序界面通常是流体运移的通道,影响界面上下低水位体系域和高水位体系域内储集层的成岩相展布,对改善储集层储集性能有利;层序体内部储集层成岩差异性明显,储集性往往受到制约。  相似文献   

苏北超基性岩某些超高压变质特征   总被引：10，自引：2，他引：8  

陆永增 《江苏地质》1998,22(1):1-9

苏北芝麻坊超基性岩体,位于大别—苏鲁超高压变质带东段的核心部位,与基性榴辉岩紧密伴生,是苏北最具代表性的岩体之一。根据多年来的成果资料,研究它的超高压变质特征,对研究整个苏鲁超高压变质带具有重大意义。对岩体的形态特征、岩相学特征、特别是矿物学特征,如镁铝榴石特征的研究,结合金刚石的选出,都有力的证实苏北超基性岩是在超高压变质环境下生成的,同时也反映其是由华北地块与扬子地块俯冲碰撞而从地壳深处挤压上来的幔源物质。  相似文献   

Deep seismic reflection and refraction profiling along the Aquitaine shelf (Bay of Biscay)   总被引：2，自引：0，他引：2  

Bertrand Pinet  Lucien Montadert  ECORS Scientific Party 《Geophysical Journal International》1987,89(1):305-312

Summary. The 300 km ECORS - Bay of Biscay profile was carried out along the Aquitaine shelf and comprised a complete set of experiments including zero-offset and 7.5 km constant offset vertical seismic reflection and six expanding spread profiles. Large offset recordings were fundamental for the definition of the layered lower crust and the Moho, while ESPs provided decisive complementary information for the geological interpretation. These data show a strong variation in crustal thickness from about 20 km beneath the rifted Parentis basin, a failed arm of the oceanic Bay of Biscay, up to 35 km to the north below the Armorican shelf, in the Hercynian domain, and to the south below the Cantabria shelf, in the vicinity of the Pyrenean deformation front. The results have important implications for the behaviour of the crust during the formation of rifted sedimentary basins and during continental collision.  相似文献   

Cassini SAR, radiometry, scatterometry and altimetry observations of Titan’s dune fields     

A. Le Gall  M.A. Janssen  A.G. Hayes  C. Savage  R.D. Lorenz  R.L. Kirk  S. Wall  E.R. Stofan  the Cassini Radar Team 《Icarus》2011,213(2):608-624

Large expanses of linear dunes cover Titan’s equatorial regions. As the Cassini mission continues, more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation (SAR, radiometry, scatterometry, altimetry) and with an increasing variety of observational geometries. In this paper, we report on Cassini’s radar instrument observations of the dune fields mapped through May 2009 and present our key findings in terms of Titan’s geology and climate. We estimate that dune fields cover ∼12.5% of Titan’s surface, which corresponds to an area of ∼10 million km², roughly the area of the United States. If dune sand-sized particles are mainly composed of solid organics as suggested by VIMS observations (Cassini Visual and Infrared Mapping Spectrometer) and atmospheric modeling and supported by radiometry data, dune fields are the largest known organic reservoir on Titan. Dune regions are, with the exception of the polar lakes and seas, the least reflective and most emissive features on this moon. Interestingly, we also find a latitudinal dependence in the dune field microwave properties: up to a latitude of ∼11°, dune fields tend to become less emissive and brighter as one moves northward. Above ∼11° this trend is reversed. The microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion (relative to that of the dune), roughness and degree of sand cover. In agreement with radiometry and scatterometry observations, SAR images suggest that the fraction of interdunes increases northward up to a latitude of ∼14°. In general, scattering from the subsurface (volume scattering and surface scattering from buried interfaces) makes interdunal regions brighter than the dunes. The observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north, thus allowing wave penetration in the underlying substrate. Altimetry measurements over dunes have highlighted a region located in the Fensal dune field (∼5° latitude) where the icy bedrock of Titan is likely exposed within smooth interdune areas. The hemispherical assymetry of dune field properties may point to a general reduction in the availability of sediments and/or an increase in the ground humidity toward the north, which could be related to Titan’s asymmetric seasonal polar insolation. Alternatively, it may indicate that either the wind pattern or the topography is less favorable for dune formation in Titan’s northern tropics.  相似文献   

Distribution and interplay of geologic processes on Titan from Cassini radar data     

R.M.C. Lopes  E.R. Stofan  J. Radebaugh  G. Mitri  R.L. Kirk  J.I. Lunine  R. Lorenz  L. Wye  R.J. Ollerenshaw  A. LeGall  R. West  P. Callahan  P. Valora  the Cassini RADAR Team 《Icarus》2010,205(2):540-558

The Cassini Titan Radar Mapper is providing an unprecedented view of Titan’s surface geology. Here we use Synthetic Aperture Radar (SAR) image swaths (Ta-T30) obtained from October 2004 to December 2007 to infer the geologic processes that have shaped Titan’s surface. These SAR swaths cover about 20% of the surface, at a spatial resolution ranging from ∼350 m to ∼2 km. The SAR data are distributed over a wide latitudinal and longitudinal range, enabling some conclusions to be drawn about the global distribution of processes. They reveal a geologically complex surface that has been modified by all the major geologic processes seen on Earth - volcanism, tectonism, impact cratering, and erosion and deposition by fluvial and aeolian activity. In this paper, we map geomorphological units from SAR data and analyze their areal distribution and relative ages of modification in order to infer the geologic evolution of Titan’s surface. We find that dunes and hummocky and mountainous terrains are more widespread than lakes, putative cryovolcanic features, mottled plains, and craters and crateriform structures that may be due to impact. Undifferentiated plains are the largest areal unit; their origin is uncertain. In terms of latitudinal distribution, dunes and hummocky and mountainous terrains are located mostly at low latitudes (less than 30°), with no dunes being present above 60°. Channels formed by fluvial activity are present at all latitudes, but lakes are at high latitudes only. Crateriform structures that may have been formed by impact appear to be uniformly distributed with latitude, but the well-preserved impact craters are all located at low latitudes, possibly indicating that more resurfacing has occurred at higher latitudes. Cryovolcanic features are not ubiquitous, and are mostly located between 30° and 60° north. We examine temporal relationships between units wherever possible, and conclude that aeolian and fluvial/pluvial/lacustrine processes are the most recent, while tectonic processes that led to the formation of mountains and Xanadu are likely the most ancient.  相似文献