地表覆盖分类成果质量特征分析   总被引：1，自引：1，他引：0  

商建伟 《测绘通报》2020,(9):159-161

自我国全面建成地理国情普查成果库之后，工作重心由全面普查变为重点监测。不论普查还是监测，准确地对地表覆盖进行分类一直是工作的重点和难点。在常态化监测阶段，把握地表覆盖分类成果的主要质量指标，归纳其诸如变化率、变化区域分布、变化类型，分析影响其成果质量的主要因素，对监测生产组织及质量控制具有非常重要的作用。  相似文献   

Diagnosing snow accumulation errors in a rain‐snow transitional environment with snow board observations          下载免费PDF全文

Nicholas E. Wayand  Martyn P. Clark  Jessica D. Lundquist 《水文研究》2017,31(2):349-363

Diagnosing the source of errors in snow models requires intensive observations, a flexible model framework to test competing hypotheses, and a methodology to systematically test the dominant snow processes. We present a novel process‐based approach to diagnose model errors through an example that focuses on snow accumulation processes (precipitation partitioning, new snow density, and snow compaction). Twelve years of meteorological and snow board measurements were used to identify the main source of model error on each snow accumulation day. Results show that modeled values of new snow density were outside observational uncertainties in 52% of days available for evaluation, while precipitation partitioning and compaction were in error 45% and 16% of the time, respectively. Precipitation partitioning errors mattered more for total winter accumulation during the anomalously warm winter of 2014–2015, when a higher fraction of precipitation fell within the temperature range where partition methods had the largest error. These results demonstrate how isolating individual model processes can identify the primary source(s) of model error, which helps prioritize future research.  相似文献   

Explicit integration of a porosity‐dependent hydro‐mechanical model for unsaturated soils          下载免费PDF全文

Yue Zhang  Annan Zhou 《国际地质力学数值与分析法杂志》2016,40(17):2353-2382

An adaptive substepping explicit integration scheme is developed for a porosity‐dependent hydro‐mechanical model for unsaturated soils. The model is referred to as the modified σ –Θ model in this paper, which features the employment of the subloading surface plasticity and the stress–saturation approach. On numerical aspects, convex/nonconvex subloading surfaces in the σ –Θ space may result in incorrect loading–unloading decisions during the integration. A new loading–unloading decision method is developed here to solve the problem and then embedded into the explicit integration scheme for the modified σ –Θ model. In addition, to enhance the accuracy of the explicit integration, local errors from both hydraulic and mechanical components are included in the error control for each substep. A drift correction method is also developed to ensure the state point lies on the subloading surface in the σ –Θ space within a set error level. The performance of the loading–unloading decision method for the modified σ –Θ model is discussed through comparing it with the conventional loading–unloading decision method. The importance of involving the hydraulic component in the error control is also demonstrated. The accuracy and efficiency of the proposed adaptive substepping explicit integration scheme for the modified p–Θ model are also studied via several numerical examples. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Numerical modeling of toxic nonaqueous phase liquid removal from contaminated groundwater systems: mesh effect and discretization error estimation          下载免费PDF全文

Chongbin Zhao  Thomas Poulet  Klaus Regenauer‐Lieb 《国际地质力学数值与分析法杂志》2015,39(6):571-593

Numerical modeling has now become an indispensable tool for investigating the fundamental mechanisms of toxic nonaqueous phase liquid (NAPL) removal from contaminated groundwater systems. Because the domain of a contaminated groundwater system may involve irregular shapes in geometry, it is necessary to use general quadrilateral elements, in which two neighbor sides are no longer perpendicular to each other. This can cause numerical errors on the computational simulation results due to mesh discretization effect. After the dimensionless governing equations of NAPL dissolution problems are briefly described, the propagation theory of the mesh discretization error associated with a NAPL dissolution system is first presented for a rectangular domain and then extended to a trapezoidal domain. This leads to the establishment of the finger‐amplitude growing theory that is associated with both the corner effect that takes place just at the entrance of the flow in a trapezoidal domain and the mesh discretization effect that occurs in the whole NAPL dissolution system of the trapezoidal domain. This theory can be used to make the approximate error estimation of the corresponding computational simulation results. The related theoretical analysis and numerical results have demonstrated the following: (1) both the corner effect and the mesh discretization effect can be quantitatively viewed as a kind of small perturbation, which can grow in unstable NAPL dissolution systems, so that they can have some considerable effects on the computational results of such systems; (2) the proposed finger‐amplitude growing theory associated with the corner effect at the entrance of a trapezoidal domain is useful for correctly explaining why the finger at either the top or bottom boundary grows much faster than that within the interior of the trapezoidal domain; (3) the proposed finger‐amplitude growing theory associated with the mesh discretization error in the NAPL dissolution system of a trapezoidal domain can be used for quantitatively assessing the correctness of computational simulations of NAPL dissolution front instability problems in trapezoidal domains, so that we can ensure that the computational simulation results are controlled by the physics of the NAPL dissolution system, rather than by the numerical artifacts. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

双能CT成像基材料分解法的理论误差分析     

郑鹏  郝佳  邢宇翔 《CT理论与应用研究》2011,20(2):153-162

双能X射线计算机断层成像技术(DECT)能够准确地重建物质的有效原子序数和电子密度信息,是一种有效的物质辨别技术.基材料分解法是求解DECT重建问题的主要方法之一.但目前应用此方法得到的重建结果误差较大,并且对于金属伪影抑制能力也较差.本文分析了DECT基材料分解法重建结果的误差来源和形成机制,阐释了其对金属伪影抑制作...  相似文献   

太湖水量平衡影响因素分析及误差控制措施研究   总被引：2，自引：1，他引：1  

申金玉  石亚东  高怡  莫李娟  陈润 《水文》2011,31(3):60-63

本文在搜集2001~2008年太湖水量平衡中各个计算要素的基础上,分析计算太湖水量平衡的绝对误差及相对误差。究其原因,误差产生的影响因素主要有测验手段、风浪、巡测线内的产流、农业用水等。根据对影响因素分析,本文有针对性地提出了误差控制措施,重点是要加强测验手段及频次,从而减小水量平衡误差,为太湖水量分配方案提供更加精准的数据基础和依据。  相似文献   

提高气介式超声波水位计测量精度的探讨   总被引：1，自引：0，他引：1  

黄新建  周五一 《水文》2011,(4):71-75

分析了影响气介式超声波水位计水位测量精度的各种因素,提出了消除这些影响因素的对策措施。其中,对超声波水位计测量回波因距离、反射角和发射面的变化带来的误差进行了分析,提出了一种利用数字采样技术对超声波测量回波前沿进行分析补偿来提高测量精度的方法。采用该技术的气介式超声波水位计在回波信号强弱变化时,数据重复性明显提高,使较短时间的采样就可获得较好测量精度,适合野外功耗要求小而采用间歇工作的方式。  相似文献   

水深测量误差分析与改正     

褚宏宪  周小明  史慧杰  冯京 《物探与化探》2011,35(3):358-363

影响水深测量精度的因素较多,水深测量误差主要有仪器误差、声速误差、潮位观测误差、船速误差和船只因素,较全面进行了测量误差原因分析,针对作业过程,提出采取提高测量精度措施,并通过应用实例说明应用注意事项。  相似文献   

减小离散误差的时频峰值滤波算法   总被引：1，自引：0，他引：1  

林红波  李月  徐学纯  马海涛 《吉林大学学报(地球科学版)》2011,41(2):572-578

提出减少时频峰值滤波分段点处阶跃误差的改进方法。经过研究时频峰值滤波在频率调制和时频平面峰值滤波时产生的离散误差以及尺度变换方式,发现分段点处阶跃误差与离散傅里叶变换的长度成反比,且与零点在尺度变换后产生的不确定值有关。提出基于定零点尺度变换的时频峰值滤波,在信号尺度变换时将零点变换到瞬时频率区间上的固定值,使各段时频峰值滤波零点偏移量一致,从而消除分段点处的阶跃误差。仿真实验和实际地震信号时频峰值滤波处理结果表明,改进的时频峰值滤波算法能够有效消减随机噪声,减少分段滤波在分段处的阶跃。  相似文献   

基于GPS单点测速的海浪测量方法初探     

单瑞  刘焱雄  赵铁虎  冯义楷 《海洋通报》2011,30(5):529-534

首先分析比对了已有的测波方法,阐述了将GPS单点测速应用到测波中的优点.然后讨论了基于多普勒频移的测速方法,并分析了各类误差对测速精度的影响.最后利用静态数据进行动态测速模拟试验和实测动态数据测速与RTK (Real Time Kinematic,实时动态测量系统)位置差分测速进行—致性检验.结果表明,使用静态数据采用...  相似文献