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11.
由于电磁波无法在水中传播,导致海底地震仪(OBS)与全球定位系统(GPS)无法进行实时对钟,因此会产生一定的时钟漂移.而受船时、海况等影响,被动源OBS在回收后往往电量亏损,致使设备回收时并没有完成对钟,无法直接利用对钟前后的时钟漂移量进行线性校正.本文选取中国科学院海洋研究所2016—2017年间在雅浦俯冲带进行的长周期被动源OBS实验所获得的数据,利用背景噪声互相关方法对OBS进行了时间校正.结果发现,各OBS在经过一年左右时间的布放后,时钟漂移量在1～3 s之间,且基本呈线性趋势,将该结果平均分配到每天从而完成线性校正.另外,探讨了时钟的非线性漂移、误差源、参考台站的选取等因素对时钟准确度的影响,为OBS的数据处理进行了有益的探索. 相似文献
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A physically constrained wavelet-aided statistical model (PCWASM) is presented to analyse and predict monthly groundwater dynamics on multi-decadal or longer time scales. The approach retains the simplicity of regression modelling but is constrained by temporal scales of processes responsible for groundwater level variation, including aquifer recharge and pumping. The methodology integrates statistical correlations enhanced with wavelet analysis into established principles of groundwater hydraulics including convolution, superposition and the Cooper–Jacob solution. The systematic approach includes (1) identification of hydrologic trends and correlations using cross-correlation and multi-time scale wavelet analyses; (2) integrating temperature-based evapotranspiration and groundwater pumping stresses and (3) assessing model prediction performances using fixed-block k-fold cross-validation and split calibration-validation methods. The approach is applied at three hydrogeologicaly distinct sites in North Florida in the United States using over 40 years of monthly groundwater levels. The systematic approach identifies two patterns of cross-correlations between groundwater levels and historical rainfall, indicating low-frequency variabilities are critical for long-term predictions. The models performed well for predicting monthly groundwater levels from 7 to 22 years with less than 2.1 ft (0.7 m) errors. Further evaluation by the moving-block bootstrap regression indicates the PCWASM can be a reliable tool for long-term groundwater level predictions. This study provides a parsimonious approach to predict multi-decadal groundwater dynamics with the ability to discern impacts of pumping and climate change on aquifer levels. The PCWASM is computationally efficient and can be implemented using publicly available datasets. Thus, it should provide a versatile tool for managers and researchers for predicting multi-decadal monthly groundwater levels under changing climatic and pumping impacts over a long time period. 相似文献
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This research aims to examine the multiscale-multifractal correlation properties between the geomagnetic storm and coronal mass ejection (CME) occurrences by analyzing the CME linear speed and Planetary K-index time series data. The relevant data for both CME and geomagnetic storm occurrences were obtained from the Solar and Heliospheric Observatory mission's LASCO and the NOAA Space Weather Prediction Center, respectively, for the same period (February 1999 to December 2007). We performed MultiFractal cross-correlation Detrended Fluctuation Analysis (MFXDFA) and Multifractal cross-correlation Detrending Moving average Analysis (MFXDMA) to investigate and quantify the possible cross-correlation between the two natural events. The MFXDFA technique is also compared to the backward MFXDMA algorithm's performance. The change in the degree of cross-correlation over time has been investigated, and the findings are quantitatively analyzed. The existence of significant power-law cross-correlations has been discovered within all scaling orders. Furthermore, we also find evident persistence of cross-correlation with substantial Hurst exponents. In addition, it has been observed that long-term cross-correlation has a more considerable degree of multifractality and persistence than short-term cross-correlation. 相似文献
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A new algorithm to correct the orientation error of the accelerometerat the Dahan Downhole Array, Hualien, Taiwan is developed. This algorithmconsists of three stages: (1) rotating two horizontal ground motions on thefree surface to the SH-SVdirection and SH axis offers a reference direction.(2) computing the synthetic downhole SH waves at a downhole station and (3)searching a rotation angle for downhole observation that yields a best waveformmatch between the synthetic and observed downhole seismograms. At this point, the rotated angle corresponding to the best waveform match can be considered as the orientation error. We selected five earthquakes with good data qualityfor analysis. Results show that this algorithm gives a more stable estimationthan a conventional method because it allows the selection of data from a wider time window for analyses. The estimated orientation error of the accelerometers at the Dahan Downhole Array after the 1999 reinstallation are40°, 114° and 285° at depths of 50, 100 and 200 m, respectively. 相似文献
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GE Renyan 《地球空间信息科学学报》2013,16(1):29-32
ABSTRACT With the help of CCD images, the realization of high precision positioning and measurement has become the basic standard for machine vision and real time photogrammetry systems. However, deformation and other sorts of degradation occurring during transmission are major limiting factors of the precision attainable with most current CCD cameras and frame grabbers. So a precise radiometric and geometric transmission of images from CCD sensor to memory is a fundamental aspect of CCD camera calibration. The geometric calibration system, which uses some image processing algorithms of the CCD camera based on the researched and developed system is discussed. The reliability and validity are also discussed. The experimental results for the calibration of the CCD array will be taken as an important quality index for CCD evaluation. 相似文献
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A study of the lithogeochemistry of metavolcanics in the Ben Nevis area of Ontario, Canada has shown that factor analysis methods can distinguish lithogeochemical trends related to different geological processes, most notably, the principal compositional variation related to the volcanic stratigraphy and zones of carbonate alteration associated with the presence of sulphides and gold. Auto- and cross-correlation functions have been estimated for the two-dimensional distribution of various elements in the area. These functions allow computation of spatial factors in which patterns of multivariate relationships are dependent upon the spatial auto- and cross-correlation of the components. Because of the anisotropy of primary compositions of the volcanics, some spatial factor patterns are difficult to interpret. Isotropically distributed variables such as CO2 are delineated clearly in spatial factor maps. For anisotropically distributed variables (SiO2), as the neighborhood becomes smaller, the spacial factor maps becomes better. Interpretation of spatial factors requires computation of the corresponding amplitude vectors from the eigenvalue solution. This vector reflects relative amplitudes by which the variables follow the spatial factors. Instability of some eigenvalue solutions requires that caution be used in interpreting the resulting factor patterns. A measure of the predictive power of the spatial factors can be determined from autocorrelation coefficients and squared multiple correlation coefficients that indicate which variables are significant in any given factor. The spatial factor approach utilizes spatial relationships of variables in conjunction with systematic variation of variables representing geological processes. This approach can yield potential exploration targets based on the spatial continuity of alteration haloes that reflect mineralization.List of symbols ci Scalar factor that minimizes the discrepancy between andUi - D Radius of circular neighborhood used for estimating auto- and cross-correlation coefficients - d Distance for which transition matrixU is estimated - dij Distance between observed valuesi andj - E Expected value - Ei Row vector of residuals in the standardized model - F(dij) Quadratic function of distancedij F(dij)=a+bdij+cdij2 - L Diagonal matrix of the eigenvalues ofU - i Eigenvalue of the matrixU;ith diagonal element ofL - N Number of observations - p Number of variables - Q Total predictive power ofU - R Correlation matrix of the variables - R0j Variance-covariance signal matrix of the standardized variables at origin;j is the index related tod andD (e.g.,j=1 ford=500 m,D=1000 m) - R1j Matrix of auto- and cross-correlation coefficients evaluated at a given distance within the neighborhood - Rm2 Multiple correlation coefficient squared for themth variable - Si Column vectori of the signal values - sk2 Residual variance for variablek - Ti Amplitude vector corresponding toVi;ith row ofT=V–1 - T Total variation in the system - U Nonsymmetric transition matrix formed by post-multiplyingR01–1 byRij - Ui Componenti of the matrixU, corresponding to theith eigenvectorVi;Ui=iViTi - U*i ComponentUi multiplied byci - Uij Sum of componentsUi+Uj - Vi Eigenvector of the matrixU;ith column ofV withUV=VL - w Weighting factor; equal to the ratio of two eigenvalues - Xi Random variable at pointi - xi Value of random variable at pointi - yi Residual ofxi - Zi Row vectori for the standardized variables - zi Standardized value of variable 相似文献
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Jian-Yin Nie Shuang-Nan Zhang Department of Physics Center for Astrophysics Tsinghua University Beijing Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2007,7(2):199-208
We apply a Cross-Correlation (CC) method developed previously for detecting gamma-ray point sources to the WMAP first year data by using the Point-Spread Function of WMAP and obtain a full sky CC coefficient map. We find that the CC method is a pow- erful tool to examine the WMAP foreground residuals which can be further cleaned accord- ingly. Evident foreground signals are found in the WMAP foreground cleaned maps and the Tegmark cleaned map. In this process 101 point sources are detected, and 26 of them are new sources additional to the originally listed WMAP 208 sources. We estimate the ?ux of these new sources and verify them by another method. As a result, a revised mask file based on the WMAP first year data is produced by including these new sources. 相似文献
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广州市登革热时空传播特征及影响因素 总被引：3，自引：0，他引：3
以广州市主城区为研究区,着眼于街道等微观尺度,首先通过实地调查分析法、核密度分析法、标准差椭圆法,探究登革热时空传播特征;其次结合交叉相关性分析法与地理探测器,分析温度、湿度、气压、用地类型对登革热传播的影响,讨论了不同用地类型交互作用与登革热扩散的关系。研究表明：1）登革热时空传播具明显的阶段性特征,多发生于居住环境较差、人口密度较高的区域,并快速向外扩散;2)登革热发展初期,以输入型病例为主;3）环境较差、老年人口众多、人员构成复杂、交通便捷的老城区是登革热高爆发风险区域;4）温度、湿度、气压对登革热传播存在显著滞后性影响关系,温度、湿度与登革热传播呈正相关关系,气压与登革热传播呈负相关关系;5）居民人口分布与登革热传播关系最为密切,池塘、农田、草地、公共绿地交互地区会增加登革热传播风险。 相似文献
