北斗导航信号源发展现状分析     

谢金石 《全球定位系统》2012,37(5):52-55,75

北斗导航信号源是检测北斗用户机性能的重要测试设备,它通过仿真卫星星座、卫星星钟、电离层等环境效应、用户轨迹等来模拟再现北斗导航卫星信号。分析了国内外导航信号源的发展现状以及信号源的功能特点,指出未来导航信号源的发展趋势。  相似文献   

基础和屋顶隔震混凝土结构的地震振动台实验研究   总被引：5，自引：2，他引：3  

韩传峰  李春祥  张群慧 《地震工程与工程振动》2004,24(1):141-147

通过使用平面尺寸为4.0m×4.0m的地震模拟器即振动台,对基础和屋顶隔震体系的控制性能进行了比较研究。试验包括三个三层无隔震、基础隔震和屋顶隔震混凝土框架结构模型。屋顶隔震包括板和叠层橡胶支座(LRB)。输入振动台的模拟地震动分别是1940N-S地震动、人工模拟山东地震动和人工模拟上海地震动。通过分析三个三层模型在白噪音扫描下的动力特性,首先评价了基础隔震与屋顶隔震体系的控制性能。实验结果显示,尽管基础隔震与屋顶隔震有着不同的工作原理,但基础隔震和屋顶隔震体系都能够明显地减小结构的位移和加速度响应(包括层间位移)。而且前者有更好的有效性。值得注意的是,屋顶隔震体系由于实施相对方便,因而可能成为减小中低层建筑结构地震损伤的优先选择。  相似文献   

静水压力变化对NTC热敏电阻器电学特性影响     

刘遵京  王军华  汤新强  霍鹏  刘熠  姚金城  常爱民 《海洋与湖沼》2022,53(3):569-577

负温度系数(negative temperature coefficient,NTC)热敏电阻器由于在窄温区内具有极高的灵敏度,在海洋领域中有着广泛的应用,但深海应用中固有的高静水压力,对器件的测温准确度造成不利影响。为了更好地认识这种现象,以珠状NTC热敏电阻器为研究对象,利用海洋环境高压模拟装置,开展了静水压力作用对器件电学特性影响的研究,固定环境温度25℃和0℃,压力范围0~60 MPa,步长5 MPa。结果显示,随着静水压力的增大,NTC热敏电阻器的电阻值减小;环境温度25℃和0℃时,5~60 MPa的静水压力造成的漂移分别为-0.11%~-2.81%、-0.19%~-2.78%,等效于温度漂移分别为0.024~0.624℃、0.036~0.535℃。这为热敏电阻器在深海温度准确测量的提升提供了指引,有利于在海洋测温领域中更好的应用。  相似文献   

Hydrology of stockpiled industrial coal exposed to rainfall     

K. J. Curran  I. G. Droppo  K. N. Irvine 《水文研究》2002,16(14):2781-2790

The movement of water and particulate matter through a simulated coal pile using a rainfall–coal‐pile simulator is investigated. In conjunction with coal‐pile management practices, this study indicates that coal‐pile systems change their internal and surficial structure with successive rainstorm events. This change in coal‐pile structure alters the proportions, rates and suspended solid concentrations within surface runoff and infiltration during subsequent storm events. Results demonstrate the need to determine the optimal coal‐pile slope that minimizes water contact time, but at the same time minimizes the potential for mass wasting and rill erosion. Promotion of a compacted surface is beneficial for the minimization of solids removal, and a stormwater detention pond with potential flocculant additive is suggested as a viable remedial measure for the containment and treatment of coal‐pile runoff. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Jason-1 Altimeter Ground Processing Look-Up Correction Tables     

P. THIBAUT  L. AMAROUCHE  O. Z. ZANIFE  N. STEUNOU  P. VINCENT  P. RAIZONVILLE 《Marine Geodesy》2013,36(3-4):409-431

Poseidon-2 is the dual frequency radar altimeter embarked on the CNES/NASA oceanographic satellite Jason-1 that was launched on 7 December 2001. The primary objective of the Jason-1 mission is to continue the high accuracy time series of altimeter measurements that began with TOPEX in 1992. To achieve this goal, it is necessary to improve each component of the ground processing continually. Among these components are the look-up correction tables that are used to correct the estimations (range, significant waveheight, and sigma naught) issued from the retracking algorithms (on-board and ground). Look-up tables were first computed taking into account the prelaunch characteristics of the altimeter. They have to be updated to take into account better all the in-flight characteristics of the altimeter and all the updated ground algorithms that can impact the estimation process. The aim of this article is to describe the radar altimeter simulator of performances that has been used to compute look-up tables, to display the freshly computed look-up tables, and to discuss the consequences of these new corrections on the products provided to the users. The updated look-up correction tables allow improvement of SWH estimation, in particular with respect to TOPEX SWH data. It is also shown that no range dependency on SWH has to be looked for in these tables, and that the on-board TOPEX and Poseidon-2 tracking systems may contain the differences explaining the relative sea state bias between both altimeters.  相似文献   

The interaction between hydrology and geomorphology in a landscape simulator experiment     

Greg Hancock  Garry Willgoose 《水文研究》2001,15(1):115-133

An experimental landscape simulator has been developed which uses a rainfall simulator to create overland flow and erosion. The simulator uses rainfall sprinklers that eliminate rainsplash and an artificial soil which has little cohesion. Experimental landscapes developed in the simulator evolved according to Howard's headward growth model. Elements of Glock's model could be identified during evolution (i.e. initiation and maximum extension), but other stages of this model were not observed (i.e. extension and integration). The Horton concept of cross‐grading and micropiracy and stream piracy was not observed despite the dominance of overland flow, nor the groundwater headward growth mechanism proposed by Dunne, the latter due to experimental design, which eliminated any perched groundwater table. The experimental apparatus produced model landscapes that are scaled‐down analogues of real world processes. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Using on‐nadir spectral reflectance to detect soil surface changes induced by simulated rainfall and wind tunnel abrasion     

Adrian Chappell  Ted M. Zobeck  Gillian Brunner 《地球表面变化过程与地形》2005,30(4):489-511

The surface susceptibility to erosion (erodibility) is an important component of soil erosion models. Many studies of wind erosion have shown that even relatively small changes in surface conditions can have a considerable effect on the temporal and spatial variability of dust emissions. One of the main difficulties in measuring erodibility is that it is controlled by a number of highly variable soil factors. Collection of these data is often limited in scale because in situ measurements are labour‐intensive and very time‐consuming. To improve wind erosion model predictions over several spatial and temporal scales simultaneously, there is a requirement for a non‐invasive approach that can be used to rapidly assess changes in the compositional and structural nature of a soil surface in time and space. Spectral reflectance of the soil surface appears to meet these desirable requirements and it is controlled by properties that affect the soil erodibility. Three soil surfaces were modified using rainfall simulation and wind tunnel abrasion experiments. Observations of those changes were made and recorded using digital images and on‐nadir spectral reflectance. The results showed clear evidence of the information content in the spectral domain that was otherwise difficult to interpret given the complicated interrelationships between soil composition and structure. Changes detected at the soil surface included the presence of a crust produced by rainsplash, the production of loose erodible material covering a rain crust and the selective erosion of the soil surface. The effect of rainsplash and aeolian abrasion was different for each soil tested and crust abrasion was shown to decrease as rainfall intensity increased. The relative contributions of the eroded material from each soil surface to trapped mixtures of material assisted the erodibility assessment. Ordination analyses within each of two important soil types explained significant amounts of the variation in the reflectance of all wavebands by treatments of the soil and hence changes in the soil surface. The results show that soil surface conditions within a soil type are an underestimated source of variation in the characterization of soil surface erodibility and in the remote sensing of soil. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The production of digital elevation models for experimental model landscapes     

Greg Hancock  Garry Willgoose 《地球表面变化过程与地形》2001,26(5):475-490

Automated digital photogrammetry was used to produce digital elevation models of experimental model landscapes under controlled laboratory conditions as part of a series of rainfall erosion experiments looking at the evolution of landforms in response to erosion. The method allowed the elevations of the experimental landscapes to be studied in great detail on a regular grid digital terrain map with relatively very little effort. Digital photogrammetry produced elevation data at a resolution of 6 mm with a standard deviation of 2·0 mm over an experimental catchment relief of approximately 200 mm; this resolution is considerably better than that achievable by conventional manual photogrammetry. The density of grid points was sufficiently high that small‐scale details such as knickpoints developing in channels were represented. The method can facilitate the study of both experimental and natural landscapes in great detail. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Evaluating the importance of accessibility to congestion response using a GIS-based travel simulator     

Irene Casas 《Journal of Geographical Systems》2003,5(1):109-127

 This paper examines the effect of accessibility on individual response to unexpected traffic delays and congestion. The dataset used was collected by means of a travel simulator developed within a geographic information system (GIS) environment. The simulator models a commute trip where congestion takes place, and subjects are asked to respond by making a choice among alternative courses of action. Available alternatives for dealing with the unexpected traffic delay include changing the location of the planned activities or changing the activities to be performed. Accessibility to the new locations and to the different activities is computed using a cumulative measure. Analysis using CHAID tree technique found that accessibility is a good predictor of subjects' choice when responding to unexpected traffic delays. Received: September 2002 / Accepted: January 2003 Support for this research by a grant from the Center of Intelligent Transportation Research of the Ohio State University is gratefully acknowledged. The author would also like to thank Joe Weber, Mei-Po Kwan and two anonymous reviewers for their valuable comments.  相似文献   

An experimental and computer simulation study of erosion on a mine tailings dam wall     

G. R. Hancock  G. R. Willgoose 《地球表面变化过程与地形》2004,29(4):457-475

Mine tailings dams pose a signi?cant risk to the environment if not correctly designed, built and maintained. The effect of erosion on a back‐?lled and capped earthen dam wall was examined by construction of an analogue in an experimental model landscape simulator. The ability of a computer‐based erosion model to simulate erosion processes on the experimental structure was examined. The experimental landscape simulator uses a rainfall simulator to create overland ?ow and erode an arti?cial soil. At the commencement of rainfall, erosion occurred rapidly with deep gullies developing on the dam wall batter. The gullies developed by downcutting, with consequent bank collapse and slumping, and followed ?ow lines towards their source. A physically based erosion model (SIBERIA) was used to simulate erosion on the experimental dam wall. Erosion and consequent development of the experimental structure were modelled by SIBERIA. The ability of SIBERIA to model incision and landscape development in the experimental setting was further examined by use of a simple one‐dimensional experimental catchment. The laboratory experiment and computer simulations demonstrated that erosion on the tailings dam is driven by concentrated runoff and that runoff control is crucial to the long‐term stability of such structures. The study demonstrates that computer‐based erosion models can be used to predict how erosion occurs on the experimental landscapes examined, thus providing con?dence in their use and application. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献