Normal moveout velocity for pure‐mode and converted waves in layered orthorhombic medium          下载免费PDF全文

Igor Ravve  Zvi Koren 《Geophysical Prospecting》2016,64(5):1235-1258

We study the azimuthally dependent hyperbolic moveout approximation for small angles (or offsets) for quasi‐compressional, quasi‐shear, and converted waves in one‐dimensional multi‐layer orthorhombic media. The vertical orthorhombic axis is the same for all layers, but the azimuthal orientation of the horizontal orthorhombic axes at each layer may be different. By starting with the known equation for normal moveout velocity with respect to the surface‐offset azimuth and applying our derived relationship between the surface‐offset azimuth and phase‐velocity azimuth, we obtain the normal moveout velocity versus the phase‐velocity azimuth. As the surface offset/azimuth moveout dependence is required for analysing azimuthally dependent moveout parameters directly from time‐domain rich azimuth gathers, our phase angle/azimuth formulas are required for analysing azimuthally dependent residual moveout along the migrated local‐angle‐domain common image gathers. The angle and azimuth parameters of the local‐angle‐domain gathers represent the opening angle between the incidence and reflection slowness vectors and the azimuth of the phase velocity ψ_phs at the image points in the specular direction. Our derivation of the effective velocity parameters for a multi‐layer structure is based on the fact that, for a one‐dimensional model assumption, the horizontal slowness and the azimuth of the phase velocity ψ_phs remain constant along the entire ray (wave) path. We introduce a special set of auxiliary parameters that allow us to establish equivalent effective model parameters in a simple summation manner. We then transform this set of parameters into three widely used effective parameters: fast and slow normal moveout velocities and azimuth of the slow one. For completeness, we show that these three effective normal moveout velocity parameters can be equivalently obtained in both surface‐offset azimuth and phase‐velocity azimuth domains.  相似文献   

Rate of sedimentation in Lake Kinneret,Israel: spatial and temporal variations     

Nir Koren  Micha Klein 《地球表面变化过程与地形》2000,25(8):895-904

The rate of sedimentation in Lake Kinneret was measured over several years by means of sediment traps, in up to seven different locations in the lake. Gross sedimentation rates measured in the sediment traps vary from about 1·5 kg m⁻² a⁻¹ in the deepest part of the lake up to 10 kg m⁻² a⁻¹ near the mouth of the upper Jordan river. The rate of sedimentation near the Jordan's inflow is highly correlated to flow discharge in the river, while in the centre of the lake the seasonal sedimentation pattern is mainly correlated to the bloom period of Peridinium gatunense. During the bloom period of Peridinium gatunense sedimentation rates all over the lake are very similar, indicating that the Peridinium is evenly distributed in the lake. The average suspended sediment discharge of the upper Jordan river flowing into the lake is 41 000 ton a⁻¹.Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Classification-based vehicle detection in high-resolution satellite images     

Line Eikvil  Lars Aurdal  Hans Koren 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(1):65-72

In this study, we have looked into the problem of vehicle detection in high-resolution satellite images. Based on the input from the local road authorities, we have focused not only on highways, but also on inner city roads, where more clutter is expected. The study site is the city of Oslo, Norway. To do vehicle detection in these areas, we propose an automatic approach, consisting of a segmentation step, followed by two stages of object classification. In the process, we utilize multispectral images, panchromatic images and a road network. The approach has been tested on Quickbird images, and the results that are obtained have been compared with manual counts and classifications.  相似文献   

雪藻高密度连续培养中生物量和花生四烯酸的高产率   总被引：7，自引：1，他引：7  

刘建国  刘伟  Zvi Cohen  Amos Richmond 《海洋与湖沼》2002,33(5):499-508

以 1 .4cm和 2 .8cm光径的平板光生物反应器 ,恒定高光强 [2 4 0 0 μE/(m2 ·s) ],通气、无菌高密度连续培养雪地绿藻 (简称雪藻 )。连续采收并补充等量新鲜培养液 ,当藻体生物量(以去灰分干重表示 ,AFDW)达恒态时 ,研究雪藻比生长速率 (SGR)、藻体的生物产量、总脂肪酸 (TFA)和花生四烯酸 (AA)产率。结果表明 ,尽管随着比生长速率增加 ,雪藻高密度连续培养体系的AA/TFA、TFA/AFDW和AA/AFDW三个指标有不同程度的降低 ,但生物产量、总脂肪酸及其花生四烯酸产出都相当高。 2 .8cm光径的平板光生物反应器中 ,雪藻SGR为0 .2d- 1 时 ,每平方米光照面积日获 35 .3gAFDW的高产量 ;SGR 0 .1 35d- 1 时 ,TFA产率最大 ,为7.0g/(m2 ·d) ,此时AA产率也最高 ,达 2 .6g/(m2 ·d)。尽管 1 .4cm光径的反应器的培养体积比前者下降了 5 0 % ,但细胞浓度明显提高 ,单位光照面积的AFDW和TFA最大日产率只下降了37.3%和 1 0 % ,分别为 2 2 .1和 6.3g/(m2 ·d) ,而AA的最大日产率也是 2 .6g/(m2 ·d)。结果还表明 ,氮或磷营养亏缺能明显提高雪藻AA含量的各项指标 ,同时高光强也有利于雪藻累积AA。  相似文献   

A weather-resolving index for assessing the impact of climate change on tourism related climate resources   总被引：2，自引：1，他引：1  

Gongmei Yu  Zvi Schwartz  John E. Walsh 《Climatic change》2009,95(3-4):551-573

This study develops and tests a Modified Climate Index for Tourism (MCIT) utilizing more than 50 years of hourly temperature, wind and significant weather data from contrasting climatic regions, Florida and Alaska. The index measures climate as a tourism resource by combining several tourism-related climate elements. It improves previous methods by incorporating variables that are more relevant to tourism activities, by addressing the overriding nature of some conditions, and by incorporating hourly observations rather than simple daily averages. The MCIT was tested using hourly weather observations from King Salmon, Alaska and Orlando, Florida. The results show that average temperature alone is not sufficient to represent tourism climate resources. For example, at both the Florida and Alaskan sites, showers and thunderstorms are more limiting factors than temperature during much of the year. When applied to past climate data, the proposed MCIT generates meaningful results that capture tourism-related climate variations and trends, including (a) the increasingly favorable tourism conditions in Alaska due to a lengthening of the warm season and (b) a decrease of ideal climatic conditions in central Florida due to the increased summer temperatures. Thus, the index has the potential to become a useful quantitative tool to be used in conjunction with climate models to predict the nature and magnitude of the impact of anticipated climate changes on tourism.  相似文献   

Stress distribution over the Mozambique Ridge     

Vladimir Lyakhovsky  Zvi Ben-Avraham  Margaret Reznikov 《Tectonophysics》1994,240(1-4):21-27

The Mozambique Ridge is an aseismic oceanic plateau in the southwestern Indian Ocean. During the separation of Antarctica and South Africa in the Early Cretaceous, the Mozambique Ridge was segmented by fracture zones which were assumed to become inactive during the Cenomanian, when Africa and Antarctica were finally separated. However, the existence of active normal faulting in the central part of the Mozambique Ridge was demonstrated by single and multichannel seismic surveys. Numerical modelling of the stress distribution caused by the crustal structure of the Mozambique Ridge and the adjacent oceanic basins suggests the possible existence of a zone with average horizontal tension up to 70 MPa along the central part of this passive ridge, which may cause the modern fault activity. These stresses also cause an additional dynamic anomaly which can explain small variations of the geoid anomaly over the ridge.  相似文献   

Features of Variations in the F2-Layer Critical Frequency During the Sudden Stratospheric Warnings of 1966–2009 According to Data from Kaliningrad and Irkutsk Stations     

Timchenko  A. V.  Bessarab  F. S.  Koren’kov  Yu. N.  Koren’kova  N. A.  Borchevkina  O. P.  Ratovsky  K. G. 《Geomagnetism and Aeronomy》2021,61(1):100-107

Geomagnetism and Aeronomy - A study of the wave changeability in the F2-layer critical frequency over Kaliningrad (54.6° N, 20° E) and Irkutsk (53° N, 103° E) stations during...  相似文献   

Eigenrays in 3D heterogeneous anisotropic media,Part II: Dynamics     

Igor Ravve  Zvi Koren 《Geophysical Prospecting》2021,69(1):28-52

This paper is the second in a sequel of two papers and dedicated to the computation of paraxial rays and dynamic characteristics along the stationary rays obtained in the first paper. We start by formulating the linear, second‐order, Jacobi dynamic ray tracing equation. We then apply a similar finite‐element solver, as used for the kinematic ray tracing, to compute the dynamic characteristics between the source and any point along the ray. The dynamic characteristics in our study include the relative geometric spreading and the phase correction due to caustics (i.e. the amplitude and the phase of the asymptotic form of the Green's function for waves propagating in 3D heterogeneous general anisotropic elastic media). The basic solution of the Jacobi equation is a shift vector of a paraxial ray in the plane normal to the ray direction at each point along the central ray. A general paraxial ray is defined by a linear combination of up to four basic vector solutions, each corresponds to specific initial conditions related to the ray coordinates at the source. We define the four basic solutions with two pairs of initial condition sets: point–source and plane‐wave. For the proposed point–source ray coordinates and initial conditions, we derive the ray Jacobian and relate it to the relative geometric spreading for general anisotropy. Finally, we introduce a new dynamic parameter, similar to the endpoint complexity factor, presented in the first paper, used to define the measure of complexity of the propagated wave/ray phenomena. The new weighted propagation complexity accounts for the normalized relative geometric spreading not only at the receiver point, but along the whole stationary ray path. We propose a criterion based on this parameter as a qualifying factor associated with the given ray solution. To demonstrate the implementation of the proposed method, we use several isotropic and anisotropic benchmark models. For all the examples, we first compute the stationary ray paths, and then compute the geometric spreading and analyse these trajectories for possible caustics. Our primary aim is to emphasize the advantages, transparency and simplicity of the proposed approach.  相似文献   

Quasi-wave variations in <Emphasis Type="Italic">foEs</Emphasis> during stratospheric warmings of 2008–2010 according to data from Kaliningrad ionospheric station     

Yu. N. Koren’kov  N. A. Koren’kova  F. S. Bessarab  V. S. Lechshenko 《Geomagnetism and Aeronomy》2017,57(4):451-460

The results of analysis of variations in the sporadic layer critical frequency (foEs) for winter periods of 2008–2010 in which sudden stratospheric warmings were observed are presented in the paper. The data were obtained at Kaliningrad ionospheric station (54.6° N, 20° E) by a Parus digital ionosonde under the usual sounding regime with an interval of 15 min. Daily mean values of foEs were used for the analysis. Solar and geomagnetic activity remained low during the periods under study, making it possible to relate the quasiwave time variations in foEs to the parameters of stratospheric warmings. The results of spectral analysis performed on the basis of continuous wavelet transform showed that, during all warmings occurring in 2008–2010, time variations in foEs show the presence of wave processes with a period of an order of 5 days and longer ones with a period of ~10—11 days. These periods coincide with characteristic periods of planetary waves observed in the atmosphere during sudden stratospheric warnings.  相似文献   

FATTY ACIDS PROFILE IN A HIGH CELL DENSITY CULTURE OF ARACHIDONIC ACID-RICH PARIETOCHLORIS INCISA （TREBOUXIOPHYCEAE, CHLOROPHYTA） EXPOSED TO HIGH PFD   总被引：1，自引：0，他引：1  

Liu Jian-guo  Zvi Cohen  Amos Richmond 《中国海洋湖沼学报》2002,20(2):149-156

The changes in arachidonic acid (AA) and fatty acids profiles along the growth curve ofParietochloris incisa, a coccoid snow green alga, were studied in a 2.8 cm light-path flat photobiorcactor, exposed to strong photon flux density [PFD, 2400 μEmol/(m²·s)]. Sixteen fatty acids were identified by gas chromatography showing that AA was the dominant fatty acid (33%–41%) followed by linoleic acid (17%–21%). AA content was closely investigated with respect to total fatty acids (TFA), ash free dry weight (AFDW) of cell mass as well as total culture content. These parameters were influenced significantly in a similar manner by culture growth phase, i.e., slightly decreasing in the lag period, gradually increasing in the logarithmic phase, becoming maximal at the early stationary phase, starting to decrease at the late stationary phase, sharply dropping at the decline phase. The increase in AA per culture volume during the logarithmic phase was not only associated with the increase in AFDW but also connected with a corresponding increase in AA/TFA, TFA/AFDW as well as AA/AFDW. The sharp decrease in AA content of the culture during the decline phase was mainly due to the decrease in AA/TFA, TFA/AFDW and AA/AFDW, although AFDW declined only a small extent. Maximal AA concentration, obtained at the early stationary phase, was 900 mg/L culture volume, and the average daily net increase of AA during 9 days logarithmic growth was 1.7 g/(m²·day). Therefore, harvesting prior to the decline phase in a batch culture, or at steady state in continuous culture mode seems best for high AA production. The latter possibility was also further confirmed by continuous culture with 5 gradients of harvesting rate. Contribution No. 4138 from the Institute of Oceanology, Chinese Academy of Sciences. Project 39970575 supported by NSFC and A/2786-2 supported by International Foundation for Sciences (IFS).  相似文献