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S. V. Goldin 《Geophysical Journal International》1984,79(1):327-337
Summary. This paper discusses the inverse (downward) continuation of a wavefield into a medium, as a means of estimating seismic velocities and the imaging of the geometry of reflecting objects. The notion of a kinematically equivalent (K-equivalent) operator of the field continuation is introduced, which allows both the possibility of replacing the initial Lamé equation by a simpler one (for example, a wave equation) and also the existence of an infinite set of continuation operators which permit us to construct a wavefield with proper characteristics. Any of the K-equivalent operators can be used in the task of imaging of reflectors given the known velocities. If velocities are unknown and reflectors are irregular, it is possible to improve the regularity of reflections by continuing the field downward to a fictitious surface in the media with a velocity Vo , that differs from the true velocity V . The conditions needed to untie loops in the true patterns in the continued field are also given.
Another approach is connected with calculations of dynamic sections using different values of velocity (say, an extremal velocity) under which the amplitudes of reflectors on sections are brought to a maximum due to the phenomena of focusing. Extremal velocities can be also used for solving inverse kinematical problems. 相似文献
Another approach is connected with calculations of dynamic sections using different values of velocity (say, an extremal velocity) under which the amplitudes of reflectors on sections are brought to a maximum due to the phenomena of focusing. Extremal velocities can be also used for solving inverse kinematical problems. 相似文献
3.
G. G. Panteleev M. N. Koshlyakov E. G. Morozov R. Yu. Tarakanov A. Yu. Goldin A. Yu. Shcherbina M. Ikeda 《Oceanology》2006,46(6):772-783
Computation of ocean currents in the Drake Passage is carried out with variational assimilation of the data of the hydrographical section across the Drake Passage carried out on December 11–15, 2003, and other data. A stream-eddy structure of the easterly Antarctic Circumpolar Current and a westerly current on the Antarctic Slope are obtained. Water transports by the different current field components and the integral transport across the Drake Passage are estimated. The necessity of direct current measurements in the Drake Passage for a correct estimate of the transport is confirmed. 相似文献
4.
Leila M. Harris Danika Kleiber Lucy Rodina Sule Yaylaci Jacqueline Goldin Germaine Owen 《社会与自然资源》2018,31(1):89-105
We analyze the relationship between perceptions of domestic water access, and quality, in relation community engagement. While others have suggested linkages between material conditions of water access and engagement (e.g., that poor water access might spur engagement), to date there have been no studies those test these relationships using statistical methods. Based on a quantitative analysis of survey data from underserved sites in Accra, Ghana, and Cape Town, South Africa, our results show that water access and quality are both predictive of community engagement. The analysis also makes a strong case that there are different dimensions when considering the material conditions of water—in this case, water access and quality each condition engagement in opposite directions. Furthermore, consistent with other studies, our study also shows different demographics (notably gender) mediate these relationships in important ways. 相似文献
5.
B. A. Goldin Yu. I. Ryabkov N. A. Sekushin L. Yu. Nazarova A. M. Askhabov 《Doklady Earth Sciences》2011,436(1):25-27
This paper details the results of a comparative study of two materials having the same structure, but drastically different
radiophysical characteristics. Corundum ceramic samples were synthesized from pure substances by firing a charge in air at
1450°C for 1 h. The second material was prepared from natural ilmenite without heat treatment using an epoxy polymer binder.
Measurements of the transmission and reflection factors within the frequency range of 8–26 GHz indicate that corundum ceramic
samples scatter electromagnetic radiation (EMR) exhibiting a pronounced dispersion of the reflection and transmission factors.
On the contrary, ilmenite samples absorb EMR showing no dispersion at all. The differences in the radiophysical characteristics
are due to the presence of magnetic impurities in the crystal lattices of corundum and ilmenite and the specific features
of the spin-phonon interaction in dielectric and ferrite materials. 相似文献
6.
S. V. Goldin 《Geophysical Journal International》1984,79(1):317-325
Summary. The first non-trivial inverse problem for media with non-horizontal reflectors z = h ( x, y ) was set up for a model of the type: V = V ( z ), 0 ≤ z ≤ h ( x, y ), and the possibility of reconstructing the functions h ( x, y ) and V ( z ) at z ↦ (min h , max h ) was shown. In the alternative case, when h = constant and V = V ( x ) there is a unique solution. Only particular cases were considered for media with h = constant, v = V ( x, z ). In the second half of the 1970s, the conditional correctness of a number of inverse problems was proved and the important concept of a sufficient data system was proposed.
Over the last 20 yr much attention has been paid to layered homogeneous media with curved interfaces, which are reflectors and refractors at the same time. The task of continuing the eikonals second derivatives played a very important role in this problem. Using the connection between the second derivatives of the CDP travel-time curve and the eikonal from a phantom source at the base of the normal ray (V. Chernyak, S. Gritsenko, T. krey) there were obtained formulae of the Dix type.
Recently methods based on linearization using a small parameter were proposed for media with slightly curved interfaces. A number of iterative algorithms for optimization and inversion have been developed, which exploit advances in the solution of direct kinematical problems. The development of the theory of inverse problems and the statistical theory of interpretation has led to the creation of a general concept of multistep algorithms and their classification. 相似文献
Over the last 20 yr much attention has been paid to layered homogeneous media with curved interfaces, which are reflectors and refractors at the same time. The task of continuing the eikonals second derivatives played a very important role in this problem. Using the connection between the second derivatives of the CDP travel-time curve and the eikonal from a phantom source at the base of the normal ray (V. Chernyak, S. Gritsenko, T. krey) there were obtained formulae of the Dix type.
Recently methods based on linearization using a small parameter were proposed for media with slightly curved interfaces. A number of iterative algorithms for optimization and inversion have been developed, which exploit advances in the solution of direct kinematical problems. The development of the theory of inverse problems and the statistical theory of interpretation has led to the creation of a general concept of multistep algorithms and their classification. 相似文献
7.
Tamara J. Goldin Kai Wünnemann H. Jay Melosh Gareth S. Collins 《Meteoritics & planetary science》2006,41(12):1947-1958
Abstract— We present the first hydrocode simulations of the formation of the Sierra Madera structure (west Texas, USA), which was caused by an impact into a thick sedimentary target sequence. We modeled Sierra Madera using the iSALE hydrocode, and here we present two best‐fit models: 1) a crater with a rim (final crater) diameter of ?12 km, in agreement with previous authors' interpretations of the original structure, and 2) a crater ?16 km in diameter with increased postimpact erosion. Both models fit some of the geologic observational data, but discrepancies with estimates of peak shock pressure, extent of deformation, and stratigraphic displacement remain. This study suggests that Sierra Madera may be a larger crater than previously reported and illustrates some of the challenges in simulating impact deformation of sedimentary lithologies. As many terrestrial craters possess some amount of sedimentary rocks in the target sequence, numerical models of impacts into sedimentary targets are essential to our understanding of target rock deformation and the mechanics of crater formation. 相似文献
8.
The POD Index, a numerical index of soil classification developed by Schaetzl and Mokma (1988) in the mesic to cryic temperature regimes of northern North America, was applied to 425 pedons in Florida to test its utility for soils in thermic and hyperthermic temperature regimes. One purpose of the POD Index is to permit approximate classification of Spodosols and similar soils in the field using soil color and morphology (horizonation) alone, without resorting to chemical analysis. In this study, a POD Index threshold value of 7 separated Florida Spodosols from non-Spodosols about 88% of the time. This study, therefore, extends the utility of the POD Index for differentiating Spodosols from non-Spodosols into the hyperthermic temperature regimes. [Key words: soils, spodic horizon, color, hyperthermic temperature regime, thermic temperature regime, POD Index.] 相似文献
9.
The distribution of the suspended particulate matter concentration in the Kara Sea is analyzed based on ship and satellite
data. The statistical relationships between the suspended matter concentration and the optical characteristics were revealed.
Charts of the distribution of the suspended matter concentration in the Kara Sea were plotted, which confirmed that the application
of optical methods for analyzing the spatial distribution of the suspended matter is effective. The most turbid waters were
observed in the Ob Gulf, Yenisei Bay, the Baidaratskaya Gulf, and the adjacent regions. The smallest concentrations of suspended
matter were observed in the central and western parts of the Kara Sea. 相似文献
10.
Results of optical studies of the Kara Sea waters are considered. The data of ship borne measurements are compared with satellite
observations. The maximum values of the beam attenuation coefficient, the chlorophyll, and the yellow substance fluorescence
were observed in the Ob gulf and in the coastal waters west of the Yamal Peninsula. The minimum values were observed in the
central and western parts of the Kara Sea. Frontal zones with sharp changes of the parameters involved were observed. The
distribution of the seawater’s optical characteristics was closely related to the hydrological structure of the Kara Sea’s
waters. The data of the shipborne measurements were consistent with the satellite observations. 相似文献