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41.
Aimed at the initial value problem of the particular second-order ordinary differential equations,y
=f(x, y), the symmetric methods (Quinlan and Tremaine, 1990) and our methods (Xu and Zhang, 1994) have been compared in detail by integrating the artificial earth satellite orbits in this paper. In the end, we point out clearly that the integral accuracy of numerical integration of the satellite orbits by applying our methods is obviously higher than that by applying the same order formula of the symmetric methods when the integration time-interval is not greater than 12000 periods. 相似文献
42.
Mimoun Boughriba Abderrahmane Melloul Yassine Zarhloule Abdelillah Ouardi 《Comptes Rendus Geoscience》2006,338(11):768-774
The succession of drought years and excessive abstraction in the plain of Triffa caused deterioration in water quality and endangers future exploitation of groundwater resources. A combination of geophysical surveys, including electrical resistivity and hydrochemical data has been used to identify the geographical extension of salinization and identify its origin. Electrical conductivity measurements are used to show the history of salinization in space and time. In this paper, a first conceptual model of the brackish springs has been established. To cite this article: M. Boughriba et al., C. R. Geoscience 338 (2006). 相似文献
43.
A cell powder factor defines the local powder factor in a simple geometric procedure that accounts for the charge in each blast hole and the triangulation formed by blast hole collars in a blast pattern. In the case of asymmetric blast patterns, the cell powder factor deviates from the global powder factor. Poor drilling of blast hole collars produces significant variation in the cell powder factor, more so, than does poor blast hole charging. The cell powder factor does not account for timing within a blast and does not easily handle non-parallel blast hole configurations. The cell powder factor is best used as a design or audit tool before blast holes are loaded. It gives the opportunity to correct for poor drilling and/or poor charging practices prior to firing a blast. 相似文献
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对河北大麻坪宝石级橄榄石物理化学及宝石学特征进行研究后,初步提出矿床成因模式,对于相似地区的碱性玄武岩地区的橄榄石宝石矿床的勘探有指导意义。 相似文献
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Low-low satellite-to-satellite tracking: a comparison between analytical linear orbit perturbation theory and numerical integration 总被引:1,自引:0,他引:1
P.N.A.M. Visser 《Journal of Geodesy》2005,79(1-3):160-166
Low-low satellite-to-satellite tracking (ll-SST) range-rate observations have been predicted by two methods: one based on a linear perturbation theory in combination with the Hill equations, and one based on solving the equations of motion of two low-flying satellites by numerical integration. The two methods produce almost equivalent Fourier spectra of the range-rate observations after properly taking into account a few resonant terms. For a typical GRACE-type configuration, where the two satellites trail each other at a distance of 300 km at an altitude of 460 km, and in the presence of the EGM96 gravity field model, complete to spherical harmonic degree and order 70, the agreement between the Fourier spectra is about 1 mm/s compared to a root-mean-square (RMS) value of more than 220 mm/s for the range-rate signal. The discrepancy of 1 mm/s can be reduced significantly when not taking into account perturbations caused by the J2 term. Excluding the J2 term, the agreement between the two methods improves to 0.4 mm/s compared to a RMS value of 6 mm/s for the range-rate signal. These values are 0.01 and 2.3 mm/s when ignoring the spectrum for frequencies below two cycles per orbital revolution, reducing the discrepancy even further to about 0.5% of the signal. The selected linear perturbation theory is thus capable of modeling gravity field induced range-rate observations with very high precision for a large part of the spectrum. 相似文献
49.
Trevor Quinn A.-Xing Zhu James E. Burt 《International Journal of Applied Earth Observation and Geoinformation》2005,7(4):324-338
Hydro-ecological modelers often use spatial variation of soil information derived from conventional soil surveys in simulation of hydro-ecological processes over watersheds at mesoscale (10–100 km2). Conventional soil surveys are not designed to provide the same level of spatial detail as terrain and vegetation inputs derived from digital terrain analysis and remote sensing techniques. Soil property layers derived from conventional soil surveys are often incompatible with detailed terrain and remotely sensed data due to their difference in scales. The objective of this research is to examine the effect of scale incompatibility between soil information and the detailed digital terrain data and remotely sensed information by comparing simulations of watershed processes based on the conventional soil map and those simulations based on detailed soil information across different simulation scales. The detailed soil spatial information was derived using a GIS (geographical information system), expert knowledge, and fuzzy logic based predictive mapping approach (Soil Land Inference Model, SoLIM). The Regional Hydro-Ecological Simulation System (RHESSys) is used to simulate two watershed processes: net photosynthesis and stream flow. The difference between simulation based on the conventional soil map and that based on the detailed predictive soil map at a given simulation scale is perceived to be the effect of scale incompatibility between conventional soil data and the rest of the (more detailed) data layers at that scale. Two modeling approaches were taken in this study: the lumped parameter approach and the distributed parameter approach. The results over two small watersheds indicate that the effect does not necessarily always increase or decrease as the simulation scale becomes finer or coarser. For a given watershed there seems to be a fixed scale at which the effect is consistently low for the simulated processes with both the lumped parameter approach and the distributed parameter approach. 相似文献
50.
Desertification is a severe stage of land degradation, manifested by “desert-like” conditions in dryland areas. Climatic conditions together with geomorphologic processes help to mould desert-like soil surface features in arid zones. The identification of these soil features serves as a useful input for understanding the desertification process and land degradation as a whole. In the present study, imaging spectrometer data were used to detect and map desert-like surface features. Absorption feature parameters in the spectral region between 0.4 and 2.5 μm wavelengths were analysed and correlated with soil properties, such as soil colour, soil salinity, gypsum content, etc. Soil groupings were made based on their similarities and their spectral reflectance curves were studied. Distinct differences in the reflectance curves throughout the spectrum were exhibited between groups. Although the samples belonging to the same group shared common properties, the curves still showed differences within the same group.Characteristic reflectance curves of soil surface features were derived from spectral measurements both in the field and in the laboratory, and mean reflectance values derived from image pixels representing known features. Linear unmixing and spectral angle matching techniques were applied to assess their suitability in mapping surface features for land degradation studies. The study showed that linear unmixing provided more realistic results for mapping “desert-like” surface features than the spectral angle matching technique. 相似文献