Shape analysis and multispectral classification in geological remote sensing     

Andrea G. Fabbri  Freek D. van der Meer  Carlos R. Valenzuela  Cornelius A. Kushigbor 《Mathematical Geology》1993,25(7):773-793

This paper discusses the usage of mathematical morphology in image processing of remotely-sensed data for geologic interpretation. Particular attention is given to noise-reducing transformations of spectral bands before and after different methods of classification, and to the usage of textural context. The development of a viable processing strategy requires a multidisciplinary approach and expert knowledge in different areas: (a) geology, geomorphology, and vegetation in a study area, (b) properties of the sensor for imagery photointerpretation, (c) spectral/spatial properties of the digital data within an integrated dataset (remote sensing and ancillary data), and (d) data-processing tools including mathematical morphology theory. Examples of geometric characterization of Canadian LANDSAT scenes are described in which shape measurements are obtained using a PC-based hybrid image-processing and geographic information system, termed ILWIS, which was developed at ITC, in the Netherlands. Classes from supervised and unsupervised classification are compared to guide in geological mapping. Classes over individual occurrences of broad vegetation-landform units are studied to aid in environmental mapping. Field knowledge is the context necessary to construct expert procedures to drive sequences of data-processing steps toward a target result such as optimal classification, enhancement, or feature extraction. The interaction between expert rules and the image-processing steps can be based on synthetic measurements of shape to quantize the information either spatially or spectrally. Many useful geometrical transformations of spatially-distributed data are extensions or generalizations of spatial analysis functions typical of geographic information systems.  相似文献   

A four-parameter,two degree-of-freedom block-spring model: Effect of the driver velocity     

Jose L. Brun  Javier B. Gomez 《Pure and Applied Geophysics》1994,143(4):633-653

We analyze the effect of tectonic plate velocities in the earthquake pattern using a simple mass-spring model of the Burridge and Knopoff type with two blocks and a velocity-weakening friction law. Previous versions of the two-block model assume a steady driver during slip events (limit of zero driver velocity), which, in some cases makes necessary the introduction of artificial parameters to start the numerical integration of the equations of motion at impending slip of any block. Still maintaining the condition of zero driver velocity during slip, we shall introduce a procedure to start the numerical integration without introducing artificial parameters and this will be done by using a linearized version of the equations of motion valid for small velocities and considering nonzero driver velocity. We also introduce a four parameter model in which the driver velocity enters the equations during the whole simulation, and analyze the effect of the new parameter, the driver velocity, in the displacement and time patterns of blocks motion, directly related to earthquake statistics such as coseismic slips and average repeat times.  相似文献   

Book reviews     

F. Alejandro Nava  Manfred Koch  Andrzej Hanyga  Jacek Leliwa-Kopystyński  Frazer Tabeart  Sueo Veno  Andrzej W. Wernik  Yu. N. Korenkov  Kenji Satake  Carlos Lozano  Aysel Karafistan  Ian N. James  Anthony Dore  Jacek Wałczewski  Krzysztof Haman  Brian F. Farrell 《Pure and Applied Geophysics》1994,143(4):753-780

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Asymptotic Theory For Diffusive Electromagnetic Imaging     

Jean Virieux  Carlos Flores-Luna  Dominique Gibert 《Geophysical Journal International》1994,119(3):857-868

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The infrared dielectric properties of maghemite, γ-Fe2O3, from reflectance measurement on pressed powders     

Carlos Pecharromán  T. González-Carreño  Juan E. Iglesias 《Physics and Chemistry of Minerals》1995,22(1):21-29

The infrared complex permittivity functions of three varieties of maghemite, γ-Fe₂O₃, having different degrees of vacancy ordering, have been determined from their IR reflectance spectra, measured at near to normal incidence on pressed powder pellets. The optical constants therefrom obtained have been verified by using them in the simulation of the corresponding absorption spectra for KBr-diluted pellets, and these are in excellent agreement with the experimental spectra. All calculations are based on a procedure for the estimation of the effective dielectric function of a mixture, which incorporates percolation features, recently developed by the authors.  相似文献   

A comparison of windows and maximum entropy methods for MT transfer function estimation     

Carlos Emilio Moyano

Ana Marí  a Osella 《Physics of the Earth and Planetary Interiors》1990,60(1-4):62-67

The ability of the Maximum Entropy Spectral Estimate (MEM) to handle magnetotelluric signals was investigated. To this end simulations of naturally occurring signals and real data were spectral analyzed both by a standard FFT technique and by MEM. The method developed for the simulation of the time series, provides accurate amplitudes and phase, and turns out to be a good test procedure for spectral analysis methods, as they apply to MT signal processing. The final estimation of the apparent resistivity was better achieved by the FFT technique. Oscillations were observed in the estimation of the apparent resistivities by MEM.  相似文献   

Regional gravity investigation of Honduras, Central America     

Mark E. Ander  Carlos L.V. Aiken  Maricio F. De la Fuente 《Journal of Volcanology and Geothermal Research》1991,45(1-2)

A regional gravity study of Honduras was performed as part of a major study of the geothermal resource potential of Honduras. This study was conducted by Los Alamos National Laboratory, in cooperation with the Honduras government. Regional offshore free-air and onshore Bouguer gravity maps, and residual/isostatic gravity maps of Honduras and surrounding regions were produced. From these data several regional crustal and upper mantle models were produced. These models pass through two local geothermal sites, Platanares and San Ignacio. The regional geologic and tectonic implications of the models and their relevance to the geothermal potential of Honduras and to six well known geothermal sites in particular are examined. No obvious regional structures observed in the gravity data can explain the thermal enhancement in general or the specific geothermal sites. More local tectonic or structural conditions must control the distribution of the thermally enhanced areas.  相似文献   

Geophysical investigations of the Platanares geothermal site, Honduras, Central America     

Carlos L. Aiken  Mark E. Ander  Mauricio F. de la Fuente 《Journal of Volcanology and Geothermal Research》1991,45(1-2)

Geophysical studies were carried out in Platanares in Western Honduras, as part of an investigation of the geothermal resource potential of Honduras by Los Alamos National Laboratory in cooperation with the Honduran government and the U.S. Geological Survey. Geological and geochemical studies later followed by exploratory bore-holes indicate this area of rugged topography has the best geothermal potential in Honduras. In order to better understand the geology of the area, gravity, audiomagnetotelluric and telluric surveys were carried out. The site is in a graben of Tertiary volcanics and Cretaceous red beds, with numerous hot springs along faults in the center of the graben. Gravity mapped the thickness of low-density tuffs and the position of associated normal faults. It also indicated the presence of persuasive, shallow, highly silicified, high-density tuffs and gravels. The electrical surveys mapped shallow, high-resistivity silicified zones and faults as low-resistivity zones. The red beds below the tuffs are considered to contain the geothermal reservoir, but their maximum thickness could not be determined by these surveys due to the lack of density contrast and the high surface electrical conductivities. Three geologic cross-sections constructed by others have been re-evaluated using gravity modeling and analysis of eletrical anomalies, showing general agreement but in detail significant differences.  相似文献   

Possible climatic impacts of tropical deforestation     

Eneas Salati  Carlos A. Nobre 《Climatic change》1991,19(1-2):177-196

Large-scale conversion of tropical forests into pastures or annual crops will likely lead to changes in the local microclimate of those regions. Larger diurnal fluctuations of surface temperature and humidity deficit, increased surface runoff during rainy periods and decreased runoff during the dry season, and decreased soil moistrue are to be expected.It is likely that evapotranspiration will be reduced because of less available radiative energy at the canopy level since grass presents a higher albedo than forests, also because of the reduced availability of soil moisture at the rooting zone primarily during the dry season. Recent results from general circulation model (GCM) simulations of Amazonian deforestation seem to suggest that the equilibrium climate for a grassy vegetation in Amazonia would be one in which regional precipitation would be significantly reduced.Global climate changes probably will occur if there is a marked change in rainfall patterns in tropical forest regions as a result of deforestation. Besides that, biomass burning of tropical forests is likely adding CO₂ into the atmosphere, thus contributing to the enhanced greenhouse warming.  相似文献   

The alleged kimberlite-carbonatite relationship: evidence from ilmenite and spinel from Premier and Wesselton mines and the Benfontein sill,South Africa     

Gaspar  Jose C.  Wyllie  Peter J. 《Contributions to Mineralogy and Petrology》1984,85(2):133-140

Carbonate-rich, SiO₂-poor residua are developed in some kimberlites solidifying as ocelli, layers, or discrete dikes which satisfy petrographic definitions of carbonatite. Arguments that these rocks have mineralogies, antecedents, and comagmatic rocks differing from those of the carbonatites in alkaline rock complexes, including the specific observation that kimberlites and carbonatites contain ilmenites and spinels of different composition, have been used to refute the alleged kimberlite-carbonatite relationship. New microprobe analyses of ilmenites and spinels from carbonate-rich rocks associated with kimberlites in three South African localities correspond to spinels and ilmenites of carbonatites from alkalic complexes, or have characteristics intermediate between those of carbonatites and kimberlites. The ilmenites are distinguished from kimberlite ilmenites by higher MnO, FeTiO₃, and Nb₂O₅, and by negligible Cr₂O₃. The spinels are distinguished from kimberlite spinels by their Al₂O₃ and Cr₂O₃ contents. There is clearly a genetic relationship between the kimberlites and the carbonate-rich rocks, despite the observation that their ilmenites and spinels are distinctly different, which indicates that the same observation is not a valid argument against a petrogenetic relationship between kimberlites and carbonatites. These rocks are among the diverse products from mantle processes influenced by CO₂, and we believe that the petrogenetic links among them are forged in the upper mantle. We see insufficient justification to deny the name carbonatite to carbonate-rich rocks associated with kimberlites if they satisfy the petrographic definition in terms of major mineralogy.  相似文献