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61.
This study was to detect dryland degradation coupling linear spectral unmixing model of Landsat images with syndrome concept in temperate dryland system, Minqin, China. The phenological contrast and complementation between green vegetation fraction in summer, sandland fraction and saline land fraction in spring, was firstly structured to quantify degradation characteristics by simple correlation analysis with ground data. The spatiotemporal patterns of the three degradation indicators were interpreted with the help “dust bowl” syndrome, qualitatively deciphered the degradation causal clusters, loops and important consequences in the study area. The results indicate water-using and distribution pattern was changed, agricultural intensity and productivity increased, salinization lessened in oasis, whereas sandification risk heightened. This approach developed in this study, has the potentially broad applicability, for dryland system monitoring and modelling. 相似文献
62.
We measure the 2-1 cumulant correlator power spectrum, a degenerate three-point statistic or integrated bispectrum, from the WMAP first and three year data releases (WMAP1 and WMAP2, respectively). We present a method of estimating these statistics using the pseudo-Cl-based SpICE estimator. We interpret the measurements in a maximum likelihood framework using theoretical predictions based on the simplest fNL model. All calculations are repeated on Monte Carlo simulations to obtain covariance matrices of our measurements. Application of the theory of random matrices revealed that the experimental covariances are consistent with a random matrix approximation. Finally, our χ2 analysis yields fNL = 22 ± 52(1σ) from WMAP2. 相似文献
63.
Chen Jin ling 《成都信息工程学院学报》1989,(2)
本文简单介绍了LVDT、相敏检波器和三角波发生器的工作原理及自行设计的一种实用的LVDT相敏检波读出电路。 相似文献
64.
Adrian C. Armstrong 《水文研究》1988,2(4):383-389
Linear system theory can be used to model and predict watertable responses to precipitation inputs in an artificially drained field. The response function is mathematically equivalent to the Unit Hydrograph concept familiar to hydrologists. This paper shows that it is possible to derive such response functions, and comments on the problems encountered in their derivation. Response functions for two contrasted sites are presented, and the possibilities for their use discussed. 相似文献
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An integrated linear/non-linear flow model for the conduit-fissure-pore media in the karst triple void aquifer system 总被引:2,自引:0,他引:2
Most karstic aquifer media may be characterized as the triple-void media with highly-varied hydraulic properties, including matrix pore, fissure and conduit, in which liner flow may co-exist with non-linear flow. In this paper, an attempt is made to couple linear flow with non-linear flow in a single unified flow governing equations by introducing the concept of equivalent hydraulic conductivity (EHC) and deriving a general Darcys law for various flow. The expression of EHC in the karst conduit and fissure are also derived. The procedures of numerical implementation are demonstrated via an ideal model and a case study of karst aquifer system in the Beishan Ore Formation area, Guangxi Autonomous Region, China. 相似文献
68.
Vincent?GuenardEmail author Philippe?Drobinski Jean-Luc?Caccia Bernard?Campistron Bruno?Bench 《Boundary-Layer Meteorology》2005,115(2):263-288
We investigate the mesoscale dynamics of the mistral through the wind profiler observations of the MAP (autumn 1999) and ESCOMPTE (summer 2001) field campaigns. We show that the mistral wind field can dramatically change on a time scale less than 3 hours. Transitions from a deep to a shallow mistral are often observed at any season when the lower layers are stable. The variability, mainly attributed in summer to the mistral/land–sea breeze interactions on a 10-km scale, is highlighted by observations from the wind profiler network set up during ESCOMPTE. The interpretations of the dynamical mistral structure are performed through comparisons with existing basic theories. The linear theory of R. B. Smith [Advances in Geophysics, Vol. 31, 1989, Academic Press, 1–41] and the shallow water theory [Schär, C. and Smith, R. B.: 1993a, J. Atmos. Sci. 50, 1373–1400] give some complementary explanations for the deep-to-shallow transition especially for the MAP mistral event. The wave breaking process induces a low-level jet (LLJ) downstream of the Alps that degenerates into a mountain wake, which in turn provokes the cessation of the mistral downstream of the Alps. Both theories indicate that the flow splits around the Alps and results in a persistent LLJ at the exit of the Rhône valley. The LLJ is strengthened by the channelling effect of the Rhône valley that is more efficient for north-easterly than northerly upstream winds despite the north–south valley axis. Summer moderate and weak mistral episodes are influenced by land–sea breezes and convection over land that induce a very complex interaction that cannot be accurately described by the previous theories. 相似文献
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内蒙古气象影视服务科开发引进非线性编辑系统(以下简称非编系统)制作电视天气预报节目已有几年时间了,在实际工作中各地都积累了一些操作和使用的经验并有所改进和完善。文章根据非编系统的特点,结合平时业务工作中的使用情况,探讨其在天气预报制作中的具体运用和维护。 相似文献