The Experiment and Analysis on VLBI Observations of Space Passive Hydrogen Maser     

《Chinese Astronomy and Astrophysics》2022,46(3):297-308

China plans to establish a lunar orbital VLBI (Very Long Baseline Interferometer) station around 2025, which will carry a space passive hydrogen maser as the time and frequency reference. Since it is the first time to use a space passive hydrogen maser for VLBI observation, its feasibility needs to be studied and verified. Therefore, we carried out VLBI observations using the space passive hydrogen maser as the frequency reference. In the experiment, the active hydrogen atomic clock and space passive hydrogen maser were used as the frequency standard, and the alternate VLBI observations of China’s Mars probe TW1 (Tianwen 1) were carried out using the 25 m radio telescope at Sheshan, Shanghai, and other VLBI stations. The results of data processing and analysis show that the standard deviation of VLBI residual group delay based on both active hydrogen atomic clock and space passive hydrogen maser are within 0.5 ns, which indicates that the space passive hydrogen maser can meet the accuracy requirements of VLBI measurement for deep space exploration, and verify its feasibility as the frequency standard of lunar orbital VLBI stations.  相似文献   

Hyperspectral image noise reduction based on rank-1 tensor decomposition     

《ISPRS Journal of Photogrammetry and Remote Sensing》2013

In this study, a novel noise reduction algorithm for hyperspectral imagery (HSI) is proposed based on high-order rank-1 tensor decomposition. The hyperspectral data cube is considered as a three-order tensor that is able to jointly treat both the spatial and spectral modes. Subsequently, the rank-1 tensor decomposition (R1TD) algorithm is applied to the tensor data, which takes into account both the spatial and spectral information of the hyperspectral data cube. A noise-reduced hyperspectral image is then obtained by combining the rank-1 tensors using an eigenvalue intensity sorting and reconstruction technique. Compared with the existing noise reduction methods such as the conventional channel-by-channel approaches and the recently developed multidimensional filter, the spatial–spectral adaptive total variation filter, experiments with both synthetic noisy data and real HSI data reveal that the proposed R1TD algorithm significantly improves the HSI data quality in terms of both visual inspection and image quality indices. The subsequent image classification results further validate the effectiveness of the proposed HSI noise reduction algorithm.  相似文献   

Automatic extraction of building roofs using LIDAR data and multispectral imagery     

《ISPRS Journal of Photogrammetry and Remote Sensing》2013

Automatic 3D extraction of building roofs from remotely sensed data is important for many applications including city modelling. This paper proposes a new method for automatic 3D roof extraction through an effective integration of LIDAR (Light Detection And Ranging) data and multispectral orthoimagery. Using the ground height from a DEM (Digital Elevation Model), the raw LIDAR points are separated into two groups. The first group contains the ground points that are exploited to constitute a ‘ground mask’. The second group contains the non-ground points which are segmented using an innovative image line guided segmentation technique to extract the roof planes. The image lines are extracted from the grey-scale version of the orthoimage and then classified into several classes such as ‘ground’, ‘tree’, ‘roof edge’ and ‘roof ridge’ using the ground mask and colour and texture information from the orthoimagery. During segmentation of the non-ground LIDAR points, the lines from the latter two classes are used as baselines to locate the nearby LIDAR points of the neighbouring planes. For each plane a robust seed region is thereby defined using the nearby non-ground LIDAR points of a baseline and this region is iteratively grown to extract the complete roof plane. Finally, a newly proposed rule-based procedure is applied to remove planes constructed on trees. Experimental results show that the proposed method can successfully remove vegetation and so offers high extraction rates.  相似文献   

Validation and improvement of N1 method for pushover analysis     

《Soil Dynamics and Earthquake Engineering》2013

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Assessing leakage detectability at geologic CO2 sequestration sites using the probabilistic collocation method     

《Advances in water resources》2013

We present an efficient methodology for assessing leakage detectability at geologic carbon sequestration sites under parameter uncertainty. Uncertainty quantification (UQ) and risk assessment are integral and, in many countries, mandatory components of geologic carbon sequestration projects. A primary goal of risk assessment is to evaluate leakage potential from anthropogenic and natural features, which constitute one of the greatest threats to the integrity of carbon sequestration repositories. The backbone of our detectability assessment framework is the probability collocation method (PCM), an efficient, nonintrusive, uncertainty-quantification technique that can enable large-scale stochastic simulations that are based on results from only a small number of forward-model runs. The metric for detectability is expressed through an extended signal-to-noise ratio (SNR), which incorporates epistemic uncertainty associated with both reservoir and aquifer parameters. The spatially heterogeneous aquifer hydraulic conductivity is parameterized using Karhunen–Loève (KL) expansion. Our methodology is demonstrated numerically for generating probability maps of pressure anomalies and for calculating SNRs. Results indicate that the likelihood of detecting anomalies depends on the level of uncertainty and location of monitoring wells. A monitoring well located close to leaky locations may not always yield the strongest signal of leakage when the level of uncertainty is high. Therefore, our results highlight the need for closed-loop site characterization, monitoring network design, and leakage source detection.  相似文献   

Analysis of aftershock sequences in South and Southeastern Spain     

《Physics and Chemistry of the Earth》2013

A probabilistic modeling is used to analyze the spatio-temporal behavior of eleven aftershock sequences occurred in South and Southeastern Spain. This study focuses on the analysis of two seismicity parameters: the b-value of the frequency-magnitude distribution, and the p-value, explaining the temporal decay rate of aftershocks. The estimated b values range between 0.77 ± 0.05 and 1.18 ± 0.10 close to the typical b-values of the aftershock frequency-magnitude relationship b ≈ 1.0. The estimated p-values range between 0.75 ± 0.03 and 1.43 ± 0.10 showing broad regimes of the temporal decay of aftershocks. The modified Bath’s law used to analyze the energy partitioning, suggests that a large fraction of the accumulated energy is released in the mainshock and relatively small fraction of energy is released during aftershock sequence, for example 80% of the total energy is released during the Mula 1999 mainshock, 88% during Bullas 2002 mainshock and 87% during La Paca 2005 mainshock. The fractal dimension D₂ is estimated using the correlation integral, and then used to derive the slip ratio, as the ratio of the slip occurred on primary fault segment to the total slip. For example, we obtained a slip ratio equal to 71% for the Mula 1999 aftershock sequence, 61% for the Bullas 2002 event, 58% for the La Paca 2005 aftershock, 50% for the Lorca 2011 sequence and 63% for the sequence triggered by the Gador 2002 mainshock.Finally, the correlations between the fractal dimension, the b-value and the p-value is analyzed, and the Aki’s relation D = 3b/c is discussed as well.  相似文献   

Interaction of fluid–solid–geomembrane by the material point method     

《Computers and Geotechnics》2017

A dynamic, large deformation problem of fluid–solid–geomembrane interaction is analysed by the use of material point method, a variant of the finite element method stated in a Lagrangian–Eulerian format. A low-order element is used for space discretisation and the fluid is treated as a compressible liquid with a high value of bulk modulus. Therefore, two algorithms known from literature are applied to mitigate the effects related to the volumetric locking phenomenon. Moreover, a procedure of detecting the free surface is proposed. The method is applied to problems of determining the shape of geo-tubes, collapsing water column, and finally, to the problem of installation of a geo-container on the bed of a water reservoir. The obtained numerical outcomes are compared with the experimental results and the analytic ones when available.  相似文献   

Solar wind drivers for low-latitude ionosphere models during geomagnetic storms     

J.M. Retterer  M.C. Kelley 《Journal of Atmospheric and Solar》2010,72(4):344-349

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Validation of temperature measurements from MIPAS-ENVISAT with balloon observations obtained by MIPAS-B     

Zhang Guochang  G. Wetzel  H. Oelhaf  F. Friedl-Vallon  A. Kleinert  A. Lengel  G. Maucher  H. Nordmeyer  K. Grunow  H. Fischer 《Journal of Atmospheric and Solar》2010,72(11-12):837-847

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), a limb sounding Fourier transform interferometer in the mid-infrared band, on board the polar-orbiting ENVIronmental SATellite (ENVISAT) was launched in March 2002 by the European Space Agency (ESA). For the MIPAS data validation, three balloon flights with MIPAS-B, a balloon version of MIPAS, were carried out on the 24th and 25th of September 2002 from Aire sur l’Adour (France 44°N, 0°E), on the 20th and 21th of March, and on the 2nd and 3rd of July 2003 from Esrange, Kiruna (Sweden 68°N, 21°E). The MIPAS operational data version 4.61 for the temperature vertical profiles were compared with the correlative MIPAS-B measurements via the coincident comparison and the trajectory comparison approaches, respectively. The precision of the MIPAS temperature was estimated to be 1.04–2.48 K in the region 123–8 hPa (15–33 km) and beyond the expectation. The systematic difference shows that the absolute accuracy of the MIPAS temperature is within the total combined errors between 356 and 3 hPa (8–39 km). The agreements in the middle stratosphere are better than in the lower stratosphere and upper troposphere. The maximum difference of 1.9 K (0.9%) was found at 228 hPa (11 km). The biases of MIPAS measurements are ?0.39 K (?0.19%) and +0.25 K (+0.12%) (“+” positive bias, “?” negative bias) corresponding to the altitude regions 143–31 hPa (14–24 km) and 31–5 hPa (24–37 km), respectively.  相似文献   

基于HHT提取昆明、下关重力固体潮的地震前兆信息   总被引：15，自引：1，他引：14       下载免费PDF全文

周挚  山秀明  张立  傅容珊  梁虹  全海燕 《地球物理学报》2008,51(3):836-844

在重力固体潮地震前兆分析中引入HHT时频分析新方法.结合HHT的优越性、固体潮的特点和地震的非平稳过程特性,设计重力固体潮地震前兆分析的瞬时频率特征参数;以相应理论计算值作为参照背景,研究固体潮的震前变化特征.昆明、下关的震例分析表明, 的确存在瞬时频率特征参数的震前变化,且具短期、同步正异常特征;瞬时频率特征参数具有明确的物理意义,其震前变化反映了地震非平稳过程对理论重力固体潮的影响.  相似文献