Al-Jiboori M. H.  Xu Yumao  Qian Yongfu 《大气科学进展》2000,17(4):636-648

Micrometeorological data for wind and temperature from a 325 m high lower in Beijing City are analyzed by use of local similarty theory Non–dimentional wind and temperature gradients Φ and Φ are determined by three techniques called respectively, eddy-correlation, mean profiles and inertia subrange cospectra (ISC) method for a wide range of atmospheric stratification from unstable to stable condition Average dissipation rate Φof turbulent kinetic energy (TKE) is evaluated from u-spectrum as a quanlity required in the last technique. Ratio of the eddy transfer coefficients. α(= K / K) is calculated from Φ and Φ estimations. The results from various techniques are compared with each other and with some available empirical results in the lwor -layer. it is shown that the empirical relationship detefrmined by mean profiles and ISC methods in the lower-layer turbulence are in agreement with each other and with some other results. Supported by the National Natural Science Foundation of China under Grant No.49735170. The authors are very grateful to the members, working for the State Key Lab. of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, the Institute of Atmospheric Physics in Beijing, who supplied the data from the meteorological tower for this paper. The authors wish to thank to Mrs. Israa H. A. in the presentation of data on the required style.  相似文献   

利用地下流体氦同位素比值估算大陆壳幔热流比例   总被引：12，自引：2，他引：10  

汪洋 《地球物理学报》2000,43(6):762-770

地下流体中的氦同位素 3He来自地幔的排气作用 ,4He则是铀、钍衰变的产物 .由于铀、钍元素在大陆地壳中富集 ,4He通量与地壳热流呈正相关关系 ;同时 3He通量与地幔热流之间呈正相关 .所以地下流体的氦同位素比值 （3He / 4 He）与大陆壳幔热流比值 （qc/qm）呈反相关关系 .根据欧亚大陆和加拿大地盾的地下流体氦同位素比值数据和相应的壳幔热流比值数据 ,统计出 qc/ qm 与 3He / 4 He之间的回归关系 :qc/ qm =0 81 5- 0 30 0ln（3He / 4 He） ;此处 3He/ 4 He的单位是RA（大气的 3He/ 4 He比值 ） .有了地表热流值和壳幔热流比值即可得到地壳热流和地幔热流 .利用该公式以及热流值估算了中国主要盆地的壳幔热流值 ;根据这些数值得出的热岩石圈厚度和地壳平均生热率结果与地震学研究成果一致 .氦同位素比值是区分大陆热流中地壳热流值和地幔热流值的有用参数 .  相似文献   

Quantitative measurements on the paleo-weathering intensity of the loess-soil sequences and implication on paleomonsoon   总被引：2，自引：0，他引：2  

郝青振  郭正堂 《中国科学D辑(英文版)》2001,44(6):566-576

The loess-soil sequences in northern China provide a near continuous record of Quaternary paleoclimate. The pedogenetic intensity of the sequences is closely linked with the variations of the East Asian summer monsoon. In this study, 2181 samples from the Changwu and Xifeng loess sections are analyzed and two high-resolution paleo-weathering timeseries of the last 1.2 Ma are generated, using the ratio of CBD extractable free Fe₂O₃ (FeD) versus the total iron (FeT). This new index is compared with micromorphological features, low-frequency magnetic susceptibility, frequency-dependent magnetic susceptibility, and the Rb/Sr ratio^[5,6]. The results suggest that the FeD/FeT ratio is able to better reflect the degree of soil development. Since the chemical weathering of loess in the Loess Plateau region mainly depends upon the summer precipitation and temperature under modern climate condition, which are closely associated with strength of summer monsoon, and the chemical weathering intensity of loess primarily reflects the variations of the summer monsoon circulation.  相似文献   

X地磁垂直分量日变幅逐日比及其与地震关系的探讨   总被引：8，自引：1，他引：8  

冯志生  王建宇  蒋延林  吴晶  梅卫萍 《华南地震》2001,21(2):20-27

分析了地城关垂直分量日变幅逐日比值的高值异常与其后地震的关系，发现它们之间有良好的对应，通过分析地磁垂直分量谐波幅度的逐日比，作者认为这种高值变化可能与其间地下介质电阻率下降有关，但也有可能是是外场变化所致。  相似文献   

80年代我国人口性别比的变动及其省区差异     

杨金星 《地理研究》1993,12(4):10-14

本文根据有关资料,讨论了80年代我国人口性别比的变动特点及其省区差异,认为我国人口性别比上升的主要原因是出生性别比的变化,最后分析了人口性别比上升对我国男性婚姻的影响。  相似文献   

大别山北缘地质找矿中遥感方法的研究     

赵英时  杨忆  谭海樵  徐贵忠 《遥感学报》1994,(1)

本项工作着重探讨在植被覆盖、地质背景十分复杂的地区，利用遥感信息寻找金矿及其它多金属矿的方法。即从地层岩系、构造及构造交叉部位、蚀变带这三个方面，进行地质找矿专题信息特征提取方法的研究。最后，通过信息提取及影像综合特征，进行遥感地质制图，圈定找矿有希望的地段。  相似文献   

采用基础摩擦隔震房屋高宽比限值的研究   总被引：12，自引：3，他引：12  

李宏男  王苏岩 《地震工程与工程振动》1997,17(3):73-76

大量的试验结果和地震经验表明，采用基础隔震方法能有效地提高建筑物的抗震能力，但建筑物的高度在什么范围，即建筑物的高宽比在什么范围内才适合采用这种方法，仍然是一个有待解决的课题。本文对采用基础滑移隔震多层砌体房屋在实际地震作用下的抗倾覆高宽比限值进行了研究，利用Ｗｉｌｓｏｎ－θ数值积分方法计算，得到了多层砌体房屋的高宽比限值的统计值。其数值结果可供编制建筑隔震设计规程参考。  相似文献   

一种改进的SAR影像边缘检测方法     

刘晓君  韩芳  赵磊 《测绘通报》2017,(9):56-59

由于SAR影像具有乘性相干斑噪声,某些对光学影像有较好检测性能的边缘检测算子,对于SAR影像并不适用,因此本文提出了一种将改进后的Ratio算子与Canny算子相组合的新方法。首先采用多种客观评价指标,得出经典方法中的Lee滤波能有效去除噪声,且最大限度保留了梯度信息,适用于边缘检测;然后对边缘检测具有恒虚警特性的Ratio算子进行改进,改进后的算子更利于影像归一化处理;最后利用改进后的Ratio算子与Canny算子组合成新方法。试验结果证明,组合后的新方法显著提高了边缘检测正确率和定位精度,改善了边缘连续性,具有一定的有效性和实用性。  相似文献   

A new Likelihood Ratio for supervised classification of fully polarimetric SAR data: An application for sea ice type mapping     

《ISPRS Journal of Photogrammetry and Remote Sensing》2013

One of the potential applications of polarimetric Synthetic Aperture Radar (SAR) data is the classification of land cover, such as forest canopies, vegetation, sea ice types, and urban areas. In contrast to single or dual polarized SAR systems, full polarimetric SAR systems provide more information about the physical and geometrical properties of the imaged area. This paper proposes a new Bayes risk function which can be minimized to obtain a Likelihood Ratio (LR) for the supervised classification of polarimetric SAR data. The derived Bayes risk function is based on the complex Wishart distribution. Furthermore, a new spatial criterion is incorporated with the LR classification process to produce more homogeneous classes. The application for Arctic sea ice mapping shows that the LR and the proposed spatial criterion are able to provide promising classification results. Comparison with classification results based on the Wishart classifier, the Wishart Likelihood Ratio Test Statistic (WLRTS) proposed by Conradsen et al. (2003) and the Expectation Maximization with Probabilistic Label Relaxation (EMPLR) algorithm are presented. High overall classification accuracy of selected study areas which reaches 97.8% using the LR is obtained. Combining the derived spatial criterion with the LR can improve the overall classification accuracy to reach 99.9%. In this study, fully polarimetric C-band RADARSAT-2 data collected over Franklin Bay, Canadian Arctic, is used.  相似文献   

Seismic random noise attenuation by time-frequency peak filtering based on joint time-frequency distribution     

Chao Zhang  Hong-bo Lin  Yue Li  Bao-jun Yang 《Comptes Rendus Geoscience》2013,345(9-10):383-391

Time-Frequency Peak Filtering (TFPF) is an effective method to eliminate pervasive random noise when seismic signals are analyzed. In conventional TFPF, the pseudo Wigner–Ville distribution (PWVD) is used for estimating instantaneous frequency (IF), but is sensitive to noise interferences that mask the borderline between signal and noise and detract the energy concentration on the IF curve. This leads to the deviation of the peaks of the pseudo Wigner–Ville distribution from the instantaneous frequency, which is the cause of undesirable lateral oscillations as well as of amplitude attenuation of the highly varying seismic signal, and ultimately of the biased seismic signal. With the purpose to overcome greatly these drawbacks and increase the signal-to-noise ratio, we propose in this paper a TFPF refinement that is based upon the joint time-frequency distribution (JTFD). The joint time-frequency distribution is obtained by the combination of the PWVD and smooth PWVD (SPWVD). First we use SPWVD to generate a broad time-frequency area of the signal. Then this area is filtered with a step function to remove some divergent time-frequency points. Finally, the joint time-frequency distribution JTFD is obtained from PWVD weighted by this filtered distribution. The objective pursued with all these operations is to reduce the effects of the interferences and enhance the energy concentration around the IF of the signal in the time-frequency domain. Experiments with synthetic and real seismic data demonstrate that TFPF based on the joint time-frequency distribution can effectively suppress strong random noise and preserve events of interest.  相似文献