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411.
412.
M. C. Santos P. Vaníček W. E. Featherstone R. Kingdon A. Ellmann B. -A. Martin M. Kuhn R. Tenzer 《Journal of Geodesy》2006,80(12):691-704
Following our earlier definition of the rigorous orthometric height [J Geod 79(1-3):82–92 (2005)] we present the derivation and calculation of the differences between this and the Helmert orthometric height, which is embedded in the vertical datums used in numerous countries. By way of comparison, we also consider Mader and Niethammer’s refinements to the Helmert orthometric height. For a profile across the Canadian Rocky Mountains (maximum height of ~2,800 m), the rigorous correction to Helmert’s height reaches ~13 cm, whereas the Mader and Niethammer corrections only reach ~3 cm. The discrepancy is due mostly to the rigorous correction’s consideration of the geoid-generated gravity disturbance. We also point out that several of the terms derived here are the same as those used in regional gravimetric geoid models, thus simplifying their implementation. This will enable those who currently use Helmert orthometric heights to upgrade them to a more rigorous height system based on the Earth’s gravity field and one that is more compatible with a regional geoid model. 相似文献
413.
Vyacheslav M. Zobin Carlos J. Navarro-Ochoa Gabriel A. Reyes-Dávila 《Bulletin of Volcanology》2006,69(2):141-147
In July–August 2003, the andesitic lava dome at Volcán de Colima, México, was destroyed by a sequence of explosions that replaced the 2×106 m3 dome with a crater 200 m across and 30 m deep. The two strongest explosions occurred on July 17 and August 28. The initial low-frequency impulses that they produced, which were recorded on broadband seismic records, allowed an estimation of the counter forces of the initiating process as being equal to 0.3×1011 N and 1×1011 N for the July and August events, respectively. The seismic characteristics follow the Nishimura-Hamaguchi scaling law for volcanic explosions, reflecting self-similarity in the processes initiating explosive events. The results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the Volcanic Explosivity Index. The increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions. 相似文献
414.
V. Čermák J. Šafanda L. Bodri M. Yamano E. Gordeev 《Studia Geophysica et Geodaetica》2006,50(4):675-695
To reconstruct the recent climate history in Kamchatka, a series of repeated precise temperature logs were performed in a
number of boreholes located in a broad east-west strip (between 52 and 54°N) in the central part of Kamchatka west of Petropavlovsk-Kamchatski.
Within three years more than 30 temperature logs were performed in 10 holes (one up to six logs per hole) to the depth of
up to 400 metres. Measured temperature gradients varied in a broad interval 0 to 60 mK/m and in some holes a sizeable variation
in the subsurface temperatures due to advective heat transport by underground water was observed. Measured data were compared
with older temperature profiles obtained in the early eighties by Sugrobov and Yanovsky (1993). Even when older data are of
poorer precision (accuracy of about 0.1 K), they presented valuable information of the subsurface temperature conditions existing
20–25 years ago. Borehole observations and the inverted ground surface temperature histories (GSTHs) used for the paleoclimate
reconstruction were complemented with a detailed survey of meteorological data. Namely, the long-term surface air temperature
(SAT) and precipitation records from Petropavlovsk station (in operation since 1890) were used together with similar data
from a number of local subsidiary meteo-stations operating in Central Kamchatka since 1950. Regardless of extreme complexity
of the local meteorological/climate conditions, diversity of borehole sites and calibration of measuring devices used during
the whole campaign, the results of the climate reconstruction supported a general warming of about 1 K characteristic for
the 20th century, which followed an inexpressive cooler period typical for the most of the 19th century. In the last three
to four decades the warming rate has been locally increasing up to 0.02 K/year. It was also shown that the snow cover played
a dominant role in the penetration of the climate “signal” to depth and could considerably smooth down the subsurface response
to the changes occurred on the surface. 相似文献
415.
Effect of common point selection on coordinate transformation parameter determination 总被引:2,自引:0,他引:2
The use of satellite positioning techniques commonly requires a transformation from a Conventional Terrestrial coordinate
system to a Geodetic coordinate system, or vice versa. For such a transformation, the main problem is the determination of
transformation parameters between these coordinate systems. The transformation parameters are estimated by a least-squares
process using “common” points, i.e., those points whose coordinates are known in both systems. Therefore, the precision of
so estimated transformation parameters is closely related to certain characteristics of the common points. In this contribution,
we have formulated some theoretical relations between the transformation parameters and the number and the distribution of
common points, and corroborated the theoretical results numerically, using a simulated geodetic network. 相似文献
416.
Explicit formula for the geoid-quasigeoid separation 总被引:1,自引:0,他引:1
The explicit formula for the geoid-to-quasigeoid correction is derived in this paper. On comparing the geoidal height and
height anomaly, this correction is found to be a function of the mean value of gravity disturbance along the plumbline within
the topography. To evaluate the mean gravity disturbance, the gravity field of the Earth is decomposed into components generated
by masses within the geoid, topography and atmosphere. Newton’s integration is then used for the computation of topography-and
atmosphere-generated components of the mean gravity, while the combined solution for the downward continuation of gravity
anomalies and Stokes’ boundary-value problem is utilized in computing the component of mean gravity disturbance generated
by mass irregularities within the geoid. On application of this explicit formulism a theoretical accuracy of a few millimetres
can be achieved in evaluation of the geoid-to-quasigeoid correction. However, the real accuracy could be lower due to deficiencies
within the numerical methods and to errors within the input data (digital terrain and density models and gravity observations). 相似文献
417.
Summary A couple of different techniques for implementing the variable resolution within numerical models of the atmosphere that use
quasi-uniform grids are estimated and compared based on their merit in the simple linear advection experiments. These techniques
are: grid stretching, Schmidt transforming and grid overlapping. The quasi-uniform grids are: a conformal cubic and an octagonal
grid. The techniques for the variable resolution are evaluated from the perspective of their effects on numerical solution
and the practicality of their application. Our analysis suggests that the grid stretching is for now the most optimal choice.
However, a special form of grid overlapping is presented that has potential to become a viable alternative in the future. 相似文献
418.
E. D. Syngaevskii Yu. V. Shchegol’kov G. Ch. Vitozhents G. K. Khachatryan S. N. Petrova 《Lithology and Mineral Resources》2007,42(5):420-436
Results of the study of natural organic matter (OM) represented by classes of solid and high-molecular-compounds (resin, ozokerite, asphalt, kerite, graphite, and others) are presented. They are developed as dispersed and concentrated segregations, interlayers, and independent accumulations and impregnation in the fracture-vein system and stratiform bodies. They also accompany ore mineralization. Combination of modern tic mineralogical, chemical, isotopic, infrared spectroscopic, and X-ray photoelectron spectroscopic) analytical methods provide insight into the OM transformation during oil formation and ore genesis. Variations in OM composition and properties define the concentration of ore elements and change mechanisms of their fixation (sorption, chemosorption, and reduction). Isotopic-geochemical signs of the structural transformation of Coal and bitumen allow us to elaborate a unified scale of catagenesis and metamorphism of the sapropel-and humus-type OM. 相似文献
419.
This paper presents the development and utilisation of an automated image processing algorithm for detection and analysis
of grains. Using optical polarising microscopy, a set of colored images are collected from an area on a thin section. A filtering
operation, using rotation of a morphological alternating sequence filter (based on a structuring element), is used to remove
twinning features within individual grains. Filtering is followed by the watershed segmentation technique to determine grain
boundaries. The method is used for the identification of calcite grains in marble and the subsequent analysis of morphological
anisotropy. 相似文献
420.
I. González M. M. Jordán T. Sanfeliu M. Quiroz C. de la Fuente 《Environmental Geology》2007,52(7):1243-1251
In southern Chile, with a mild and rainy climate, high levels of heavy metals have been detected in many gold placer deposits.
Many of the contaminants pose risks to human life, and consequently damage the trofic chain in this environment. The study
zones selected correspond to the handicraft gold-bearing sands of Rio Gato (Los Muermos), Carelmapu and Cucao. These are all
located in the X Region of “Los Lagos” in Chile. The type of methodology used in the characterization of the associated mineralization
consists of testing each representative sample with a grain size distribution, statistical parameter analysis and a mineralogical
analysis, using a binocular magnifying glass, a petrographic microscope, XRD and SEM/EDX. The chemical composition was defined
by means of X ray fluorescence and micro-chemical analysis. The results of the study about sediments in southern Chile are
presented. The major concentrations of heavy minerals are generally located in areas of dynamic river energy. In the samples,
more than 70% of the heavy minerals were distributed among grain sizes corresponding to thin sand with good grain selection
(meshes of 0.25–0.06 mm). The main mineral phases present in the analysed samples were gold, zircon, olivine, ilmenite, hornblende,
hypersthene, hematite, garnet, chromite, chlorite, augite, amphibolitic-epidote, etc. The main heavy metals found as a result
of the study were mercury, lead, cadmium, chrome, tellurium, indium, zinc, cobalt, copper, platinum, gold, etc., and as well
some less common elements like cerium, praseodymium, gadolinium, neodymium, samarium and lanthanum. This research work is
only a starting point for carrying out a risk probability mapping of heavy metals and the mineralogy of the Cucao, Carelmapu
and Rio Gato gold-bearing sands. 相似文献