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The alpine meadow is widely distributed on the Tibetan Plateau with an area of about 1.2×106kn2. Damxung County, located in the hinterland of the Tibetan Plateau, is the place covered with this typical vegetation. An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux of alpine meadow from July to October,2003. The continuous carbon flux data were used to analyze the relationship between net ecosystem carbon dioxide exchange (NEE) and photosynthetically active radiation (PAR), as well as the seasonal patterns of apparent quantum yield (α) and maximum ecosystem assimilation (Pmax).Results showed that the daytime NEE fitted fairly well with the PAR in a rectangular hyperbola function, with α declining in the order of peak growth period (0.0244 μmolCO2 · μmol-1pAR) >early growth period > seed maturing period > withering period (0.0098 μmolCO2 · μmol-1pAR).The Pmax did not change greatly during the first three periods, with an average of 0.433mgCO2· m-2· s-1, i.e. 9.829 μmolCO2· m-2· s-1. However, during the withering period, Pmax was only 0.35 mgCO2 · m-2 · s-1, i.e. 7.945 μmolCO2 · m-2 · s-1. Compared with other grassland ecosystems, the α of the Tibetan Plateau alpine meadow ecosystem was much lower. 相似文献
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D. Sheeren S. Mustière J.‐D. Zucker 《International journal of geographical information science》2013,27(8):961-992
When different spatial databases are combined, an important issue is the identification of inconsistencies between data. Quite often, representations of the same geographical entities in databases are different and reflect different points of view. In order to fully take advantage of these differences when object instances are associated, a key issue is to determine whether the differences are normal, i.e. explained by the database specifications, or if they are due to erroneous or outdated data in one database. In this paper, we propose a knowledge‐based approach to partially automate the consistency assessment between multiple representations of data. The inconsistency detection is viewed as a knowledge‐acquisition problem, the source of knowledge being the data. The consistency assessment is carried out by applying a proposed method called MECO. This method is itself parameterized by some domain knowledge obtained from a second method called MACO. MACO supports two approaches (direct or indirect) to perform the knowledge acquisition using data‐mining techniques. In particular, a supervised learning approach is defined to automate the knowledge acquisition so as to drastically reduce the human‐domain expert's work. Thanks to this approach, the knowledge‐acquisition process is sped up and less expert‐dependent. Training examples are obtained automatically upon completion of the spatial data matching. Knowledge extraction from data following this bottom‐up approach is particularly useful, since the database specifications are generally complex, difficult to analyse, and manually encoded. Such a data‐driven process also sheds some light on the gap between textual specifications and those actually used to produce the data. The methodology is illustrated and experimentally validated by comparing geometrical representations and attribute values of different vector spatial databases. The advantages and limits of such partially automatic approaches are discussed, and some future works are suggested. 相似文献
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数字社区数据标准研究 总被引:4,自引:1,他引:4
当前数字社区建设缺乏统一的智能化综合管理平台以及相应的各项数据标准,使得数字社区难以真正实现统一的数字化管理。该文参考国内外相应数据标准,研究数字社区的标准体系结构。针对现有标准体系缺乏相关数据标准的现状,提出数字社区系列数据标准,包括数据接口层标准、数据分类编码标准、数据模型、数据字典和元数据标准。阐述系列标准中各标准间的相互关系以及各标准所包含的具体内容。 相似文献
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《Chinese Astronomy and Astrophysics》2019,43(2):292-304
Active hydrogen maser is the main frequency standard for establishing and maintaining the time scale. It has the characteristics of high short-term stability and low phase noise. At present, it plays an increasingly important role in the international atomic time (TAI) and various local time scales. Firstly, in combination with the internal state parameters of an active hydrogen maser, the correlation between the internal state parameters and the comparison data of a hydrogen maser is analyzed, and a method for the performance monitoring of a hydrogen maser is proposed. Secondly, according to the characteristics of hydrogen maser performance, a method for evaluating the performance of a hydrogen maser is given. The hydrogen maser performance includes mainly two aspects, namely the frequency stability and predictability. The performances of two types of active hydrogen masers (CH1-75 and MHM-2010) are evaluated by this method. The correlation analysis of the atomic clock state parameters and comparison data shows that the state parameter monitoring can effectively predict the variation of the hydrogen maser performance. The evaluation results of atomic clock frequency stability and predictability show that the atomic clock with a higher medium-and-long term frequency stability has a better predictability. There are two methods for the predictability evaluation, one is based on the data published by BIPM (Bureau International des Poids et Measures), and another one is based on the quadratic model. Both methods are consistent with the weights published by BIPM. Therefore, the two methods can be used as a quantitative method to evaluate the predictability of a hydrogen maser. 相似文献
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针对人们对地理空间数据迫切需求,介绍了多源地理空间矢量数据产生的管理与技术原因及其5种表现形式,提出了多源地理空间矢量数据集成与融合的概念及其相互关系。论述了地理数据模型的融合、地理要素语义的融合和地理数据投影和坐标系的统一是多源地理空间矢量数据集成与融合基本理论与方法。给出了实现多源数据集成的数据格式转换、数据互操作和直接数据访问方法。最后,讨论了地理要素几何位置的融合,以及通过地理要素语义融合消除地理要素数据描述和属性差异的矢量数据融合方法。 相似文献
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漆小英 《测绘与空间地理信息》2014,(12)
以南宁市六城区数字高程模型制作为例,对南宁市数字高程模型的制作过程进行了系统的阐述,由此针对制作大比例尺数字高程模型提出几点建议,最后探讨了其社会经济效益和推广前景. 相似文献
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介绍了视真电阻率ρz计算方法,通过对实际测深资料与井中电测资料的对比,证明了视真电阻率ρz的可靠性。在实际应用中可取得良好的效果。 相似文献