Noise suppression for microseismic data by non‐subsampled shearlet transform based on singular value decomposition          下载免费PDF全文

Xiaoqiang Liang  Yue Li  Chao Zhang 《Geophysical Prospecting》2018,66(5):894-903

The existence of strong random noise in surface microseismic data may decrease the utility of these data. Non‐subsampled shearlet transform can effectively suppress noise by properly setting a threshold to the non‐subsampled shearlet transform coefficients. However, when the signal‐to‐noise ratio of data is low, the coefficients related to the noise are very close to the coefficients associated with signals in the non‐subsampled shearlet transform domain that the coefficients related to the noise will be retained and be treated as signals. Therefore, we need to minimise the overlapping coefficients before thresholding. In this paper, a singular value decomposition algorithm is introduced to the non‐subsampled shearlet transform coefficients, and low‐rank approximation reconstructs each non‐subsampled shearlet transform coefficient matrix in the singular value decomposition domain. The non‐subsampled shearlet transform coefficients of signals have bigger singular values than those of the random noise, which implies that the non‐subsampled shearlet transform coefficients can be well estimated by taking only a few largest singular values. Therefore, those properties of singular value decomposition may significantly help minimise overlapping of noise and signals coefficients in the non‐subsampled shearlet transform domain. Finally, the denoised microseismic data are obtained easily by giving a simple threshold to the reconstructed coefficient matrix. The performance of the proposed method is evaluated on both synthetic and field microseismic data. The experimental results illustrate that the proposed method can eliminate random noise and preserve signals of interest more effectively.  相似文献   

Self-organizing maps for multi-scale morphometric feature identification using shuttle radar topography mission data     

Amir Houshang Ehsani  Friedrich Quiel 《国际地球制图》2013,28(5):335-355

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Earthquake‐induced landslide hazard monitoring and assessment using SOM and PROMETHEE techniques: A case study at the Chiufenershan area in Central Taiwan     

Wen‐Tzu Lin 《International journal of geographical information science》2013,27(9):995-1012

Monitoring and assessment of landslide hazard is an important task for decision making and policy planning in the landslide area. Massive landslides, caused by the catastrophic Chi‐Chi earthquake in 1999, occurred in Central Taiwan, especially at Chiufenershan area in Nantou county. This study proposed two useful indicators coupled with the Self‐organizing map (SOM) neural network and the Preference Ranking Organization METHod for Enrichment Evaluations (PROMETHEE) technique to quickly extract accurate post‐quake landslides from multi‐temporal Système Probatoire de l'Observation de la Terre (SPOT) images. A GIS‐based system was developed to simplify and integrate the procedures such as image pre‐processing, the SOM training, the PROMETHEE calculation, landslide extraction and accuracy assessment. The evaluated result shows that the landslide area soon after the earthquake is 209.50 ha (Kappa coefficient 96.88%). Over seven years of vegetation recovery, the denudation area has declined to 112.64 ha (Kappa coefficient 90.64%). Most earthquake‐induced landslides could be restored by natural vegetation succession. The developed system is a useful decision‐making tool for landslide area planning.  相似文献   

利用1:2000数字地形图编制1:10000建库数据的实践与探索     

向红梅 《测绘工程》2011,(6):45-47,52

目前,我国很多城市拥有适时更新的大比例尺数字地形图,如何利用已有资源快捷地编制中小比例尺的建库数据,值得研究和探讨.文中给出在MicroStation中利用1:2 000数字地形图编制1:10 000建库数据的方法与技术.使用数字高程模型编制等高线并结合地形和高程模型进行等高线的编辑、裁剪,采取从数字地形图上直接拾取和...  相似文献   

基于自组织神经网络算法的华北区域夏季天气气候学特征     

代刊  金荣花  胡婷 《气象》2013,39(7):801-812

对华北区域的天气气候学研究,有助于理解该区域大气环流场与地面要素场之间的相互联系。利用自组织神经网络算法(SOMs),基于1958—2002年夏季ERA-40日平均海平面气压距平场(MSLPA),对华北区域的海平面气压场进行分型,研究其天气气候特征。36种典型地面环流形势被识别出来,包括强北高南低、强西高东低槽、强西北低东南高和强东部高压西伸4种极端类型,以及它们之间的过渡型。天气型的空间特征分析表明二维自组织图上天气型的对称性体现了华北区域天气气候的一般性特征,而非对称性则体现其独特性。天气型演变特征分析表明高、低压系统越强,或以高压系统活动为主时,华北地区的天气形势相对稳定,反之则转变较快。年际变化分析指示出其中6种天气型出现较明显的年际线性变化趋势。最后,分析天气型相应的降水分布特征,表明区域内不同地区的降水来自不同天气型的影响,地面环流场的细小差别将会造成地面强降水中心位置的较大不同,且地形的影响将进一步放大该差别。上述分析结果采用更完整和更高时间分辨率的资料,定量化地研究华北区域夏季的天气分型特征,拓展其天气气候学研究。研究成果可用于发展客观化的数值模式典型天气过程识别技术,以及作为区域气候情景分析的基础。  相似文献   

地形与纬向切变基流中的非线性Rossby波   总被引：1，自引：0，他引：1       下载免费PDF全文

何建中 《热带气象学报》1993,9(2):177-184

在半地转近似下,用相角函数方法得到了含地形强迫作用与纬向切变基流的非线性常微分方程.利用微分方程解的几何定性理论,直接得到该方程存在有限振幅的周期波与孤立波解的存在条件.利用函数逼近法求得波解的显式解,得到了一些有意义的结果。  相似文献   

抚顺××厂万m~3储油罐地基沉降的综合治理     

仲大维  姬国海 《国土资源》1997,(1)

抚顺××厂３＃万ｍ３储油罐自１９９０年以来，罐体基础持续产生不均匀沉降。围绕该储油罐，通过高压定喷施工工艺，构筑定喷桩，地下防渗连续墙，在墙体内侧对罐体地基进行冲积层及基岩的直、斜孔注浆，用水泥浆液充填、胶结地基中的空化、裂隙，提高了地基强度，对减缓罐体的不均匀沉降，取得了显著成效。  相似文献   

Time series forecasting by combining the radial basis function network and the self‐organizing map     

Gwo‐Fong Lin  Lu‐Hsien Chen 《水文研究》2005,19(10):1925-1937

Based on a combination of a radial basis function network (RBFN) and a self‐organizing map (SOM), a time‐series forecasting model is proposed. Traditionally, the positioning of the radial basis centres is a crucial problem for the RBFN. In the proposed model, an SOM is used to construct the two‐dimensional feature map from which the number of clusters (i.e. the number of hidden units in the RBFN) can be figured out directly by eye, and then the radial basis centres can be determined easily. The proposed model is examined using simulated time series data. The results demonstrate that the proposed RBFN is more competent in modelling and forecasting time series than an autoregressive integrated moving average (ARIMA) model. Finally, the proposed model is applied to actual groundwater head data. It is found that the proposed model can forecast more precisely than the ARIMA model. For time series forecasting, the proposed model is recommended as an alternative to the existing method, because it has a simple structure and can produce reasonable forecasts. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Enforced self‐organizing map neural networks for river flood forecasting     

Fi‐John Chang  Li‐Chiu Chang  Yan‐Shiang Wang 《水文研究》2007,21(6):741-749

Self‐organizing maps (SOMs) have been successfully accepted widely in science and engineering problems; not only are their results unbiased, but they can also be visualized. In this study, we propose an enforced SOM (ESOM) coupled with a linear regression output layer for flood forecasting. The ESOM re‐executes a few extra training patterns, e.g. the peak flow, as recycling input data increases the mapping space of peak flow in the topological structure of SOM, and the weighted sum of the extended output layer of the network improves the accuracy of forecasting peak flow. We have investigated an ESOM neural network by using the flood data of the Da‐Chia River, Taiwan, and evaluated its performance based on the results obtained from a commonly used back‐propagation neural network. The results demonstrate that the ESOM neural network has great efficiency for clustering, especially for the peak flow, and super capability of modelling the flood forecast. The topology maps created from the ESOM are interesting and informative. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Amending Soils with Hydrogels Increases the Biomass of Nine Tree Species under Non‐water Stress Conditions     

Lawrence J. B. Orikiriza  Hillary Agaba  Mnason Tweheyo  Gerald Eilu  John David Kabasa  Aloys Hüttermann 《洁净——土壤、空气、水》2009,37(8):615-620

The classical aim of the application of super absorbent polyacrylate (SAPs) hydrogels is the prolonging of plant survival under water stress. Their effect on plant growth during non‐water stress conditions is not known. This study examined the root and shoot biomass of seedlings of nine tree species; Eucalyptus grandis, Eucalyptus citriodora, Pinus caribaea, Araucaria cunninghamii, Melia volkensii, Grevillea robusta, Azadirachta indica, Maesopsis eminii and Terminalia superba. The seedlings were potted in five soil types; sand, sandy loam, loam, silt loam and clay. These were amended at two hydrogel levels: 0.2 and 0.4% w/w and grown under controlled conditions in a green house. Root and shoot growth responses of the seedlings were determined by measuring the dry weight of the roots, stems, leaves and twigs. The addition of either 0.2 or 0.4% hydrogel to the five soil types resulted in a significant increase of the root dry weight (p < 0.001) in eight tree species compared to the controls after 8 wk of routine watering. Also, the dry weight of stems and leaves and twigs were significantly (p < 0.001) higher in the nine tree species potted in hydrogel amended soil types than in the hydrogel free controls. These results suggested that hydrogel amendment enhances the efficiency of water uptake and utilization of photosynthates of plants grown in soils which have water contents close to field capacity.  相似文献