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991.
Vegetation community structure is a key indicator of long-term vegetation change in semi-arid ecosystems. This study uses ground-based spectral measurements and a canopy reflectance model to investigate the potential of Earth observation data to characterize variations in vegetation structure along a grazing gradient in the eastern Kalahari, Botswana. Despite differences in the bidirectional reflectances of soil, plant litter, bush and grass canopies towards the end of a dry season, it is unlikely that Earth observation data can be used to estimate vegetation structure at this time. This is due to an ambiguity in the relationship between spectral reflectance and vegetation structure caused primarily by the limited dimensionality of reflectance data. Variations in canopy architecture cause differences in the level of inter-canopy shadowing but the net effect—lower reflectance with an increase in bush cover—parallels the darkening effects of any vegetation cover on relatively bright sandy soils in semi-arid environments. These results highlight the continued need for long-term ground-based ecological monitoring in conjunction with satellite-based monitoring of changes in vegetation cover. 相似文献
992.
Robust estimates of magnetotelluric and geomagnetic response functions are determined using the coherency and expected uniformity of the magnetic source field as quality criteria. The method is applied on data sets of three simultaneously recording sites. For the data acquisition we used a new generation of geophysical equipment (S.P.A.M. MkIII), which comprises novel concepts of parallel computing and networked, digital data transmission. The data-processing results show that the amount of noise on the horizontal components of the magnetic field varies considerably in time, between sites and over the frequency range. The removal of such contaminated data beforehand is essential for most data-processing schemes, as the magnetic channels are usually assumed to be free of noise. The standard remote reference method is aimed at reducing bias in response function estimates. However, this does not necessarily improve their precision as our results clearly show. With our method, on the other hand, we can filter out source field irregularities, thereby providing suitable working conditions for the robust algorithm, and eventually obtain considerably improved results. Contrary to previous concepts, we suggest rejecting as much data as feasible in order to concentrate on the remaining parts of high-quality observations. 相似文献
993.
Kees Wapenaar 《Geophysical Journal International》1998,135(2):585-594
The derivation of seismic reflection and transmission coefficients is generally based on the assumption that the medium parameters behave as step functions of depth, at least in a finite region around the interface. However, outliers observed in well logs generally behave quite differently from step functions. In this paper we represent an interface by a self-similar singularity, embedded between two homogeneous half-spaces, and we derive its frequency-dependent normal-incidence reflection and transmission coefficients. For ω → 0 the expressions for the coefficients reduce to those for a discrete boundary between two homogeneous half-spaces; for ω → ∞ they become frequency-independent. These asymptotic expressions have a relatively simple form and depend on the singularity exponent α .
The exact as well as the asymptotic expressions are used to evaluate the time-domain reflection and transmission responses of a self-similar interface. Finally, we use a numerical method to model the response of a smoothed version of a self-similar interface (note that the velocity of a smoothed singularity remains finite). It turns out that smoothing has hardly any effect on the response, provided that the smoothing does not affect the scales corresponding to the seismic frequency range. 相似文献
The exact as well as the asymptotic expressions are used to evaluate the time-domain reflection and transmission responses of a self-similar interface. Finally, we use a numerical method to model the response of a smoothed version of a self-similar interface (note that the velocity of a smoothed singularity remains finite). It turns out that smoothing has hardly any effect on the response, provided that the smoothing does not affect the scales corresponding to the seismic frequency range. 相似文献
994.
介绍了为配合闽南地震示范工程的开展而开发的《综合地震台观测资料信息管理系统》程序设计的基本原则、总体结构及功能,并给出了操作流程示意图和简要说明。 相似文献
995.
为快速准确建立相应数据库,编制了数据库管理软件。通过对四川石棉地震重点监视区地下水网点水位和气压40余万组数据的处理实践,效果很好,并已在有关单位推广应用。 相似文献
996.
Hubert CHANSON 《国际泥沙研究》1998,(3)
EXTREMERESERVOIRSEDIMENTATIONINAUSTRALIA:AREVIEWHubertCHANSON1ABSTRACTInthepaper,theauthorreviewstheproblemofreservoirsiltati... 相似文献
997.
全球震中光盘数据库3.0版,向科研单位及所有用户提供地震震中资料。包括地震震中的地理位置,震级大小及震源深度,和发震时间都存贮在光盘地震数据库。通过人机对话方式进行地震数据的存取。 相似文献
998.
999.
介绍了浅层地震折射波法在铁路桥基础勘查中的应用。使用覆盖开关,采用互换法,提高了野外数据采集速度,降低了成本。 相似文献
1000.
反射波法检测桩身完整性的一种数据处理方法 总被引:1,自引:1,他引:0
本文以纵波在杆中传播的理论为根据,介绍一种用于确定反射波往返时及视反射系数等参数的方法。将视反射系数经过一定的校正后,可定量分析反射界面的波阻抗差异的大小,进而确定桩身缺陷的严重程度;反射波往返时则用来推算桩身缺陷的位置。 相似文献