The value of a physically based model versus an empirical approach in the prediction of ephemeral gully erosion for loess-derived soils   总被引：3，自引：0，他引：3  

Jeroen Nachtergaele  J. Poesen  A. Steegen  I. Takken  L. Beuselinck  L. Vandekerckhove  G. Govers 《Geomorphology》2001,40(3-4)

A data set on soil losses and controlling factors for 58 ephemeral gullies has been collected in the Belgian loess belt from March 1997 to March 1999. Of the observed ephemeral gullies, 32 developed at the end of winter or in early spring (winter gullies) and 26 ephemeral gullies developed during summer (summer gullies). The assessed data have been used to test the physically based Ephemeral Gully Erosion Model (EGEM) and to compare its performance with the value of simple topographical and morphological indices in the prediction of ephemeral gully erosion.Analysis shows that EGEM is not capable of predicting ephemeral gully cross-sections well. Although conditions for input parameter assessment were ideal, some parameters such as channel erodibility, critical flow shear stress and local rainfall depth showed great uncertainty. Rather than revealing EGEM's inability of predicting ephemeral gully erosion, this analysis stresses the problematic nature of physically based models, since they often require input parameters that are not available or can hardly be obtained.With respect to the value of simple topographical and morphological indices in predicting ephemeral gully erosion, this study shows that for winter gullies and summer gullies, respectively, over 80% and about 75% of the variation in ephemeral gully volume can be explained when ephemeral gully length is known. Moreover, when previously collected data for ephemeral gullies in two Mediterranean study areas and the data for summer gullies formed in the Belgian loess belt are pooled, it appears that one single length (L)–volume (V) relation exists (V=0.048 L^1.29; R²=0.91). These findings imply that predicting ephemeral gully length is a valuable alternative for the prediction of ephemeral gully volume. A simple procedure to predict ephemeral gully length based on topographical thresholds is presented here. Secondly, the empirical length–volume relation can also be used to convert ephemeral gully length data extracted from aerial photos into ephemeral gully volumes.  相似文献   

青藏高原OLR的气候特征及其对北半球大气环流的影响   总被引：3，自引：5，他引：3  

李栋梁  章基嘉 《高原气象》1996,15(3):259-268

利用１９７４－１９９０年青藏高原地区地－气系统月平均射出长波辐射资料，采用ＥＯＦ方法分析了前３个特征向量场，得到了青藏高原地区地－气系统射出长波辐射的几种异常形式，阐述了它们的天气气候特征，并对不同气候区的持续 及其与北半球大气环流的关系作了研究。  相似文献   

气象场经验正交函数不同展开方案收敛性问题的探讨   总被引：15，自引：0，他引：15  

丁裕国  施能 《大气科学》1992,16(4):436-443

本文从理论上证明EOFs(经验正交函数)用于气象场时,三种不同计算方案特征值的相互关系.指出利用原始场积和矩阵展开的特征值λ_j等于用协方差阵展开的特征值λ_j~*加上平均场方差引起的特征值λ_j.进而论证了收敛速度差舁的原因.最后又以实例表明,不同展开方案的典型场意义及其与时间权重系数的对应关系.  相似文献   

三维绿色生物量的遥感模式研究与绿化环境效益估算   总被引：4，自引：0，他引：4  

周坚华  孙天纵 《遥感学报》1995,(3)

本文从理论和技术上叙述了绿量的遥感模式研究和绿化环境效益估算，并取得了以下几个方面的进展：（１）提出了绿量的概念，进一步完善了城市绿化的量化指标体系；（２）成功地修正了“逻辑斯蒂曲线”方程，并以平面量模拟立体量的方法测算了上海市全市的绿量，不仅节省了人力物力，而且提高了精度；（３）提出了模式林的概念及测定了以绿量估算绿化环境效益中所必须的标准换算量；（４）首次用绿量在全市范围估算了绿化群落的吸碳产氧、吸收二氧化硫、滞尘及夏季降温等环境效益。为分析现有绿化群落布局与结构的合理性，及为绿化规划乃至整个城市的总体规划提供了很有价值的技术参数。  相似文献   

中国东部地区断裂的缜奏性活动     

谢广林 《华南地震》1993,(3)

对中国东部地区断裂的节奏性活动进行了探讨,认为这种节奏性活动主要根据构造地貌进行鉴别,并可分为六种型式:稳定—蠕滑错动;稳定—急速错动;蠕滑—急速错动;交替型蠕滑错动;交替型急速错动和复式错动。地震活动周期与断裂的节奏性活动相关联。断裂活动产生强震的型式有单发式、对偶式和连发式,这三种形式分别出现在不同的断裂中,并取决于不同区域、不同断裂的活动特征。  相似文献   

The Ensemble Kalman Filter: theoretical formulation and practical implementation   总被引：87，自引：5，他引：82  

Geir?EvensenEmail author 《Ocean Dynamics》2003,53(4):343-367

The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.Responsible Editor: Jörg-Olaf Wolff  相似文献   

Climate change and North Sea storm surge extremes: an ensemble study of storm surge extremes expected in a changed climate projected by four different regional climate models   总被引：5，自引：0，他引：5  

Katja Woth  Ralf Weisse  Hans von Storch 《Ocean Dynamics》2006,56(1):3-15

The coastal zones are facing the prospect of changing storm surge statistics due to anthropogenic climate change. In the present study, we examine these prospects for the North Sea based on numerical modelling. The main tool is the barotropic tide-surge model TRIMGEO (Tidal Residual and Intertidal Mudflat Model) to derive storm surge climate and extremes from atmospheric conditions. The analysis is carried out by using an ensemble of four 30-year atmospheric regional simulations under present-day and possible future-enhanced greenhouse gas conditions. The atmospheric regional simulations were prepared within the EU project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects). The research strategy of PRUDENCE is to compare simulations of different regional models driven by the same global control and climate change simulations. These global conditions, representative for 1961–1990 and 2071–2100 were prepared by the Hadley Center based on the IPCC A2 SRES scenario. The results suggest that under future climatic conditions, storm surge extremes may increase along the North Sea coast towards the end of this century. Based on a comparison between the results of the different ensemble members as well as on the variability estimated from a high-resolution storm surge reconstruction of the recent decades it is found that this increase is significantly different from zero at the 95% confidence level for most of the North Sea coast. An exception represents the East coast of the UK which is not affected by this increase of storm surge extremes.  相似文献   

Towards medium-term (order of months) morphodynamic modelling of the Teign estuary, UK     

Marcos E. C. Bernardes  Mark A. Davidson  Keith R. Dyer  Ken J. George 《Ocean Dynamics》2006,56(3-4):186-197

The main objective of this paper is to address the principal mechanisms involved in the medium-term (order of months to years) morphodynamic evolution of estuaries through the application of a process-based numerical modelling. The Teign estuary (Teignmouth, UK) is the selected site. The system is forced by the macrotidal semi-diurnal tide in the English Channel and is perturbed to a minor extent by high river discharge events (freshets). Although waves have a definite influence on the adjacent coastal area, Wells (Teignmouth Quay Development Environmental Statement: Changes to Physical Processes. Report R.984c:140. ABP Marine Environmental Research Ltd., Southampton, 2002b) suggested that swell waves do not enter the estuary. Hence, wave effects are neglected in this study, as only tides and the river discharge are taken into account. The sediment grain size is highly variable, but mainly sandy. Within the frame of the COAST3D project (), four bathymetric surveys of the adjacent coastal area were carried out at a nearly weekly intervals. The outer estuary and the adjacent coastal area were also surveyed every 6 months as part of the COASTVIEW project (). Based on these data and on continuously measured parameters, such as water level, waves, wind and river discharge, numerical modelling of the morphodynamic processes can be tested. To replicate the morphological changes in the medium-term within a feasible simulation time, forcing conditions are reduced through the use of an input reduction method (called ensemble technique). In this study, simulations are based on the coupling between Telemac-2D and its non-cohesive sediment transport module, Sisyphe (version 5.3 for both modules). Three different sediment transport formulae were tested: (1) Engelund and Hansen (A monograph on sediment transport in alluvial streams, 3rd edn. Technological University of Denmark, Copenhagen, 1967) including the modifications proposed by Chollet and Cunge (J Hydraul Eng 17(1):1–13, 1979); (2) Bijker (Mechanics of sediment transport by the combination of waves and current. In: Design and reliability of coastal structures. 23rd international conference on Coastal Engineering, pp 147–173, 1968) and (3) Soulsby (Dynamics of Marine Sands. A manual for practical applications. HR Wallingford, Wallingford, p 142, 1997) modified version of van Rijn [J Hydraul Eng 110(10):1431–1456, 1984a, J Hydraul Eng 110(11):1613–1641, 1984b] formulation. Both a qualitative (i.e. visual comparison) and a quantitative tool [Brier Skill Score (BSS); described in Sutherland et al. in Coast Eng 51:917–939, 2004b] are applied to assess the similarity of simulations when compared to model predictions and observations. Tests confirmed the reliability and time efficiency of the ensemble technique, since it reproduced very well the results of a reference run, a computation based on the observed boundary conditions. For the spring-neap cycle modelled, the BSS was of 0.91 (a perfect modelling would have a BSS of 1), with a reduction in the simulation time on the order of 80%. For the 6-month-period simulation, results were also excellent: BSS=0.92 and a computer time reduction of 85%. In principle, this method has the advantage of being applied to any process-based numerical model.  相似文献   

InSAR相位分解及其在生成DEM和研究地震形变场中的应用   总被引：1，自引：1，他引：1       下载免费PDF全文

罗小军  黄丁发  刘国祥 《地震工程学报》2006,28(3):204-209,190

InSAR是极具发展潜力的微波遥感新技术,可应用于数字高程模型的产生、制图和大范围微小地表形变的测量。考虑参考面、地形和地表形变等因素,本文从几何角度分析和讨论了In-SAR的相位分解,并给出了各相位分量的函数表达式,阐述了地表高程和形变信息提取的基本原理。最后以JERS和ENVISAT卫星数据为例,展示了合成孔径雷达干涉测量在生成数字高程模型和提取地震形变场中的应用及其数据处理过程。  相似文献   

Effect of hematite on thiosulphate leaching of gold     

D. Feng  J.S.J. van Deventer 《International Journal of Mineral Processing》2007

Hematite, as a typical iron oxide slime in sulphide ore slurries, was artificially added into the leaching systems of pure gold and a sulphide ore respectively, in an attempt to investigate the effect of iron oxide slimes on the ammoniacal thiosulphate leaching of gold. The presence of hematite significantly reduced the dissolution of gold and this detrimental effect became more pronounced with increasing hematite concentration. Hematite formed coatings on gold surfaces, which could prevent leach solution from diffusing to the gold surfaces and hence, inhibit gold dissolution. Hematite catalysed the oxidative decomposition of thiosulphate to polythionates with oxygen present. XPS studies indicated a thin layer of iron oxide coating as well as the deposition of some copper and sulphur species on gold surfaces. SEM images revealed a lesser extent of corrosion for gold after leaching in the presence of hematite. The gold extraction from the sulphide ore was reduced with the addition of hematite and this effect became more noticeable with an addition of hematite at a higher concentration. A natural guar type surfactant (Gempolym M47) reduced the detrimental effect of hematite on gold extraction likely due to the prevention of hematite coating on gold and mineral particles and the dispersion of the mineral slurry. Gempolym M47 stabilised thiosulphate by weakening the interaction between cupric ions and thiosulphate and by minimising the catalytic effect of hematite on thiosulphate decomposition.  相似文献