Air quality model performance evaluation

Summary This paper reviews methods to evaluate the performance of air quality models, which are tools that predict the fate of gases and aerosols upon their release into the atmosphere. Because of the large economic, public health, and environmental impacts often associated with the use of air quality model results, it is important that these models be properly evaluated.A comprehensive model evaluation methodology makes use of scientific assessments of the model technical algorithms, statistical evaluations using field or laboratory data, and operational assessments by users in real-world applications. The focus of the current paper is on the statistical evaluation component. It is important that a statistical model evaluation exercise should start with clear definitions of the evaluation objectives and specification of hypotheses to be tested. A review is given of a set of model evaluation methodologies, including the BOOT and the ASTM evaluation software, Taylors nomogram, the figure of merit in space, and the CDF approach. Because there is not a single best performance measure or best evaluation methodology, it is recommended that a suite of different performance measures be applied. Suggestions are given concerning the magnitudes of the performance measures expected of good models. For example, a good model should have a relative mean bias less than about 30% and a relative scatter less than about a factor of two.In order to demonstrate some of the air quality model evaluation methodologies, two simple baseline urban dispersion models are evaluated using the Salt Lake City Urban 2000 field data. The importance of assumptions concerning details such as minimum concentration and pairing of data are shown. Typical plots and tables are presented, including determinations of whether the difference in the relative mean bias between the two models is statistically significant at the 95% confidence level.     

遥感变化检测技术发展综述

卫星遥感的复轨能力，稳定一致的传感器参数和系列运行计划，连续记录了地表的显著变化信息。对遥感观测到的变化信息，还需要区分是地表物理生物要素变化引起的变化，还是辐射传输路径上其它干扰因素造成的变化信息，需要从各种变化信息组分中区分目标变化信息。因此，遥感变化检测是遥感信息科学、地球系统科学、统计学和计算机技术等学科技术交叉后新的增长点，代表了当前遥感数据处理技术发展方向。为了促进遥感变化检测技术在我国的发展，收集阅读了近几年国外主要遥感刊物发表的论文、专著，综合了我国遥感变化检测技术发展现状以及大量的网络资料。     

天然洞围岩稳定性评价

天然洞体不稳定是绝对的 ,稳定是相对的。天然洞体围岩的顶板、底板、侧面三者的稳定 ,顶板的稳定最重要。顶板的稳定性 ,与天然洞体的形成原因 ,岩面的成层条件、断面形状、裂隙情况 ,漏水情况 ,天然洞体形成和稳定的时间 ,山体的地质构造条件等有关。     

高分辨率数字航测相机现状和思考

本文根据国内外数字航测相机发展的实际情况，对于新型数字航测相机视场角、影像分辨率、像移补偿、摄影间隔和影像存贮器容量、相机系统的动态定位与定向以及真彩色与多光谱摄影等技术问题进行了分析并给出了相应的结论。     

Code and carrier phase based short baseline GPS positioning: computational aspects

A recursive least squares algorithm is presented for short baseline GPS positioning using both carrier phase and code measurements. We take advantage of the structure of the problem to make the algorithm computationally efficient and use orthogonal transformations to ensure that the algorithm is numerically reliable. Details are given for computing position estimates and error covariance matrices with possible satellite rising and setting. Real data test results suggest our algorithm is effective.This research was supported by NSERC of Canada Grant RGPIN217191–99, FCAR of Quebec Grant 2001-NC-66487, and NSERCGEOIDE Network Project ENV#14 for Xiao-Wen Chang, and by NSERC of Canada Grant RGPIN9236–01 for Christopher C. Paige.The online version of the original article can be found at     

Upper mantle convection driving by density anomaly and a test model

Introduction Richter and Mckenzie (1978) supposed that there is a small-scale convection system in the mantle. For a long time lots of research provides observational data to infer the possibility of a small-scale convection in the upper mantle. For example, Haxby and Weissel (1986) discussed the relationship between SEASAT map and small-scale convection. Baudry and Kroenke (1991), Maia and Diament (1991) found that the geoid and bathymetry exhibit peaks in the 400~650 km range in the Pa…     

Three-dimensional stability analysis of the Kettleman Hills landfill slope failure based on observed sliding-block mechanism

Previous studies of the Kettleman landfill slope failure of 1988 had concluded that the failure, which slid along the underlying liner interfaces with low shearing resistance, occurred as a result of attaining the critical waste fill height. These studies showed, however, some discrepancies in regard to the adopted material strength data as well as the computed factors of safety. Based on the observed sliding-block mechanism, a 3D analysis model was established herein which allowed for variations in material strength mobilization within the sliding mass and at the slip surface. With a careful consideration on the interface strength data, results of forward analysis for the pre-slide slope generally showed better agreement with the field observations. Results of backward analysis for the post-slide slope indicated a consistency in the estimated material strength with the laboratory test data. The current study also showed slightly higher computed 3D factors of safety than the associated 2D values, in both pre-slide and post-slide cases.     

Analyzing Spatial and Temporal Changes of Aquaculture in Yunlin County,Taiwan*

This article analyzes spatial and temporal changes of aquaculture land use in Yunlin County, Taiwan, and discusses the driving forces for these changes. Digital land‐use maps and satellite imagery for 1982, 1988, 1994, and 2002 were used to extract aquaculture areas. A geographic information system was used to derive changes in aquaculture areas and to compute the spatial clustering statistics over time. A survey of eighty‐seven farmers was conducted to obtain their views and concerns about aquaculture. The results show a rapid expansion in aquaculture during the 1980s, driven mainly by exports to Japan, and a continuous decline since the mid‐1990s because of economic, environmental, and demographic factors.