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This paper presents an upscaling concept of swelling/shrinking processes of a compacted bentonite/sand mixture, which also applies to swelling of porous media in general. A constitutive approach for highly compacted bentonite/sand mixture is developed accordingly. The concept is based on the diffuse double layer theory and connects microstructural properties of the bentonite as well as chemical properties of the pore fluid with swelling potential. Main factors influencing the swelling potential of bentonite, i.e. variation of water content, dry density, chemical composition of pore fluid, as well as the microstructures and the amount of swelling minerals are taken into account. According to the proposed model, porosity is divided into interparticle and interlayer porosity. Swelling is the potential of interlayer porosity increase, which reveals itself as volume change in the case of free expansion, or turns to be swelling pressure in the case of constrained swelling. The constitutive equations for swelling/shrinking are implemented in the software GeoSys/RockFlow as a new chemo‐hydro‐mechanical model, which is able to simulate isothermal multiphase flow in bentonite. Details of the mathematical and numerical multiphase flow formulations, as well as the code implementation are described. The proposed model is verified using experimental data of tests on a highly compacted bentonite/sand mixture. Comparison of the 1D modelling results with the experimental data evidences the capability of the proposed model to satisfactorily predict free swelling of the material under investigation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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本文调研了国内外近些年在页岩油(气)微尺度流动方面的研究成果。从分子动力学方法(MD)、格子玻尔兹曼方法(LBM)、孔隙网络模型(PNM)3种计算模型的角度展开分析,同时结合作者的前期工作,分析了影响页岩油(气)流动输运的关键因素,指出3种方法的局限性及存在的问题,认为PNM方法可作为微尺度流动研究的基础模型,并将3种方法之间的联系有机地体现在研究路线框图中,为页岩油(气)微尺度流动的研究指明了方向。 相似文献
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Louis J. Durlofsky 《Mathematical Geology》2000,32(4):421-438
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遥感叶面积指数产品精度和不确定性需要通过地面测量的数据来验证。因为两者的空间尺度差异,验证前需要通过尺度转换方法将这两种数据的尺度统一。将泰勒级数展开模型进行改进后,可以用于解决叶面积指数遥感产品验证中地面测量数据与遥感产品尺度不匹配的问题,同时可以针对每个数据定量给出误差。将误差在阈值范围内的实测数据作为地面参考值对遥感产品进行验证。本文利用这种方法将黑河综合遥感联合实验数据集中的地面测量叶面积指数尺度上升到遥感像元尺度,并与MODIS,GLASS LAI遥感产品进行了比较。 相似文献
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Geoffrey J. Hay Guillermo Castilla Michael A. Wulder Jose R. Ruiz 《International Journal of Applied Earth Observation and Geoinformation》2005,7(4):339-359
Over the last decade the analysis of Earth observation data has evolved from what were predominantly per-pixel multispectral-based approaches, to the development and application of multiscale object-based methods. To empower users with these emerging object-based approaches, methods need to be intuitive, easy to use, require little user intervention, and provide results closely matching those generated by human interpreters. In an attempt to facilitate this, we present multiscale object-specific segmentation (MOSS) as an integrative object-based approach for automatically delineating image-objects (i.e., segments) at multiple scales from a high-spatial resolution remotely sensed forest scene. We further illustrate that these segments cognitively correspond to individual tree crowns, ranging up to forest stands, and describe how such a tool may be used in computer-assisted forest inventory mapping. MOSS is composed of three primary components: object-specific analysis (OSA), object-specific upscaling (OSU), and a new segmentation algorithm referred to as size constrained region merging (SCRM). The rationale for integrating these methods is that the first two provide the third with object-size parameters that otherwise would need to be specified by a user. Analysis is performed on an IKONOS-2 panchromatic image that represents a highly fragmented forested landscape in the Sooke Watershed on southern Vancouver Island, BC, Canada. 相似文献
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基于多尺度遥感数据的塔里木河干流地区植被覆盖动态 总被引：1，自引：0，他引：1
利用地面观测数据,Landsat TM和MODIS数据,基于尺度上推的研究思路,采用修正的三波段最大梯度差模型反演植被覆盖度,分析了塔里木河干流地区2000-2013年植被覆盖度时空分布及其动态变化特征。结果表明：（1）地面观测数据、Landsat TM与MODIS数据相结合进行尺度上推,尺度转换相对误差控制在4%以内,可以实现分析大范围长时间序列植被变化;（2）塔里木河干流区域植被覆盖度年内最大值出现在7、8月,2000-2013年平均植被覆盖度变化整体上呈现增长的趋势,上游年均植被覆盖度18.67%~23.67%,中游10.6%~12.44%,下游4.7%~6%,但呈现两段式发展（2000-2006年显著提高,2006-2013年小伏波动变化）;（3）塔里木河干流区域植被覆盖度空间差异明显,上游植被覆盖度增长速率最高,中游次之,下游增长速率最小。上游植被覆盖度年增长速率为0.37%,且增长趋势显著;中游年增长速率为0.06%,没有显著的变化趋势;下游年增长速率为0.05%,增长变化显著区域位于河道或稍远离河道附近及台特玛湖附近。 相似文献
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尺度效应是地理科学中普遍存在的现象,制约着遥感等空间科学的发展。发展合理的尺度转换方法以促进遥感技术的全面应用迫在眉睫。本文分别从面—面升尺度转换、点—面升尺度转换两个角度对目前定量遥感领域存在的升尺度转换方法进行综述。其中,面—面升尺度转换方法按照转换原理可分为先反演后聚合、先聚合后反演两种;点—面升尺度转换方法依据定权策略可分为简单平均法、经验回归法、地统计方法、贝叶斯方法等。不同的升尺度转换方法具有各自的特点和优势,本文分别从模型构架、基本原理、特点、局限性和适用条件等方面对现有升尺度转换方法进行分析和讨论,并从离散型与连续型、统计型与物理型、普适型与针对型以及先验知识有和无4个方面总结了现有研究中存在的不足,剖析了升尺度转换研究中存在的问题与挑战,并预测了可能的发展方向。 相似文献
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Tawanda W. Gara Andrew K. Skidmore Roshanak Darvishzadeh Tiejun Wang 《地理信息系统科学与遥感》2019,56(4):554-575
In remote sensing applications, leaf traits are often upscaled to canopy level using sunlit leaf samples collected from the upper canopy. The implicit assumption is that the top of canopy foliage material dominates canopy reflectance and the variability in leaf traits across the canopy is very small. However, the effect of different approaches of upscaling leaf traits to canopy level on model performance and estimation accuracy remains poorly understood. This is especially important in short or sparse canopies where foliage material from the lower canopy potentially contributes to the canopy reflectance. The principal aim of this study is to examine the effect of different approaches when upscaling leaf traits to canopy level on model performance and estimation accuracy using spectral measurements (in-situ canopy hyperspectral and simulated Sentinel-2 data) in short woody vegetation. To achieve this, we measured foliar nitrogen (N), leaf mass per area (LMA), foliar chlorophyll and carbon together with leaf area index (LAI) at three vertical canopy layers (lower, middle and upper) along the plant stem in a controlled laboratory environment. We then upscaled the leaf traits to canopy level by multiplying leaf traits by LAI based on different combinations of the three canopy layers. Concurrently, in-situ canopy reflectance was measured using an ASD FieldSpec-3 Pro FR spectrometer, and the canopy traits were related to in-situ spectral measurements using partial least square regression (PLSR). The PLSR models were cross-validated based on repeated k-fold, and the normalized root mean square errors (nRMSEcv) obtained from each upscaling approach were compared using one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test. Results of the study showed that leaf-to-canopy upscaling approaches that consider the contribution of leaf traits from the exposed upper canopy layer together with the shaded middle canopy layer yield significantly (p < 0.05) lower error (nRMSEcv < 0.2 for canopy N, LMA and carbon) as well as high explained variance (R2 > 0.71) for both in-situ hyperspectral and simulated Sentinel-2 data. The widely-used upscaling approach that considers only leaf traits from the upper illuminated canopy layer yielded a relatively high error (nRMSEcv>0.2) and lower explained variance (R2 < 0.71) for canopy N, LMA and carbon. In contrast, canopy chlorophyll upscaled based on leaf samples collected from the upper canopy and total canopy LAI exhibited a more accurate relationship with spectral measurements compared with other upscaling approaches. Results of this study demonstrate that leaf to canopy upscaling approaches have a profound effect on canopy traits estimation for both in-situ hyperspectral measurements and simulated Sentinel-2 data in short woody vegetation. These findings have implications for field sampling protocols of leaf traits measurement as well as upscaling leaf traits to canopy level especially in short and less foliated vegetation where leaves from the lower canopy contribute to the canopy reflectance. 相似文献