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61.
与传统检测方法相比,利用高光谱技术进行土壤有害元素砷含量的估算,具有快速、准确,成本低的特点,可对干旱区绿洲土壤有害元素砷污染进行动态监测。基于新疆渭干河-库车河三角洲绿洲耕层土壤样品的采集,获取土壤光谱数据和有害元素砷含量。通过bior1.3,db4,gaus4和mexh这4种小波基函数对土壤原始光谱反射率进行连续小波变换,并将变换后光谱数据与有害元素砷进行相关分析,以筛选出的敏感小波系数为自变量,采用偏最小二乘回归、支持向量机回归、BP神经网络和随机森林回归方法对有害元素砷含量进行高光谱反演。研究结果显示:(1)4种小波基函数在3~8尺度的光谱分解效果明显优于其他尺度,特别是4~6尺度的连续小波变换有效提升了光谱反射率与土壤有害元素砷之间的相关性,通过显著性检验的小波系数数量有了明显增多(p<0.01),在可见光的400~700 nm以及近红外的1 100~1 700和2 200~2 400 nm附近具有较强的相关性;(2)通过比较4种小波基函数对光谱数据中有效信息的辨识能力,认为小波基函数bior1.3和mexh要优于db4和gaus4,其中bior1.3的光谱分解效果最好,gaus4相对最弱;通过bior1.3第5尺度的光谱变换,与土壤有害元素砷显著相关的波段数量最多,为507个(p<0.01);(3)比较4种建模方法的反演结果发现,SVMR,BPNN和RFR模型相较于PLSR模型具有更强的估测能力,模型的估测精度更高。综合分析各模型的稳定性及估测精度后,认为bior1.3-25-RFR模型可作为研究区土壤有害元素砷的最佳估测模型。该模型的训练集和验证集的R2分别为0.893和0.639,RMSE为1.075和1.651 mg·kg-1,RPD分别为2.89和1.64,表明模型估测效果较好,稳定性较强。采用合适的小波基函数进行连续小波变换可减少土壤高光谱数据中的白噪声,挖掘出土壤光谱数据中的有效信息,对土壤有害元素砷含量的准确估测提供有力的技术保障。 相似文献
62.
Sebastian Geiger Thomas Driesner Christoph A. Heinrich Stephan K. Matthäi 《Transport in Porous Media》2006,63(3):399-434
We present a new finite element – finite volume (FEFV) method combined with a realistic equation of state for NaCl–H2O to model fluid convection driven by temperature and salinity gradients. This method can deal with the nonlinear variations
in fluid properties, separation of a saline fluid into a high-density, high-salinity brine phase and low-density, low-salinity
vapor phase well above the critical point of pure H2O, and geometrically complex geological structures. Similar to the well-known implicit pressure explicit saturation formulation,
this approach decouples the governing equations. We formulate a fluid pressure equation that is solved using an implicit finite
element method. We derive the fluid velocities from the updated pressure field and employ them in a higher-order, mass conserving
finite volume formulation to solve hyperbolic parts of the conservation laws. The parabolic parts are solved by finite element
methods. This FEFV method provides for geometric flexibility and numerical efficiency. The equation of state for NaCl–H2O is valid from 0 to 750°C, 0 to 4000 bar, and 0–100 wt.% NaCl. This allows the simulation of thermohaline convection in high-temperature
and high-pressure environments, such as continental or oceanic hydrothermal systems where phase separation is common. 相似文献
63.
Multi-address coding (MAC) lidar is a novel lidar system recently developed by our laboratory. By applying a new combined technique of multi-address encoding, multiplexing and decoding, range resolution is effectively improved. In data processing, a signal enhancement method involving laser signal demodulation and wavelet de-noising in the downlink is proposed to improve the signal to noise ratio (SNR) of raw signal and the capability of remote application. In this paper, the working mechanism of MAC lidar is introduced and the implementation of encoding and decoding is also illustrated. We focus on the signal enhancement method and provide the mathematical model and analysis of an algorithm on the basis of the combined method of demodulation and wavelet de-noising. The experimental results and analysis demonstrate that the signal enhancement approach improves the SNR of raw data. Overall, compared with conventional lidar system, MAC lidar achieves a higher resolution and better de-noising performance in long-range detection. 相似文献
64.
Solving diffusion equation using wavelet method 总被引:1,自引:0,他引:1
Xuefeng ChenJiawei Xiang 《Applied mathematics and computation》2011,217(13):6426-6432
A wavelet-based numerical method based on wavelets of Hermite cubic splines is presented for computing singularly perturbed convection-dominated diffusion equation. The advantages of the method are explained. To improve the accuracy of singular areas, wavelets are configured hierarchically for solving algebraic equations. Numerical examples show that the proposed method has good efficiency and precision. 相似文献
65.
M.M. Panja 《Applied mathematics and computation》2011,218(8):4147-4151
This note is concerned with an efficient computation of integrals of products of a smooth function and Daubechies scale function with partial support by using a one-point quadrature rule. The error estimate is obtained. The rule is illustrated by considering an example from the literature. 相似文献
66.
从具有全局最优解的几何活动轮廓方法出发,分别提出了两种基于齐次Besov窄间与小波变换的图像分割算法,并给出了解的存在性证明.数值求解利用小波软阈值以及分裂Bregman方法,能够有效提高计算效率.由于小波变换具有多分辨特性,对于包含较多细节信息的图像,采用新算法能够得到更好的分割效果.数值实验表明采用新算法能够获得较... 相似文献
67.
68.
研究了3种基于时间响应函数的结构阻尼识别方法, 包括对数衰减法、希尔
伯特方法和小波方法. 给出了3种方法的实现算法, 分析了对密集模态的识别能力.
构造仿真算例, 采用3种方法识别了5{\%}, 10{\%}和30{\%}噪声条件下的模态阻尼.
结果表明, 小波方法比对数衰减法和希尔伯特方法具有更好的噪声鲁棒性. 采用小波方法分析了润扬大桥结构健康监测系统获得的实测数据, 识别出了润扬大桥悬索桥前6阶模态参数, 第2阶和第3阶模态频率相差仅为0.015\,Hz. 研究表明, 小波方法具备噪声条件下密集模态的识别能力, 是工程中阻尼识别的优选方法. 相似文献
69.
70.
Li-Xiao Duan & Guo-Feng Zhang 《高等学校计算数学学报(英文版)》2021,14(3):714-737
The variants of randomized Kaczmarz and randomized Gauss-Seidel algorithms are two effective stochastic iterative methods for solving ridge regression
problems. For solving ordinary least squares regression problems, the greedy randomized Gauss-Seidel (GRGS) algorithm always performs better than the randomized Gauss-Seidel algorithm (RGS) when the system is overdetermined. In this paper, inspired by the greedy modification technique of the GRGS algorithm, we extend
the variant of the randomized Gauss-Seidel algorithm, obtaining a variant of greedy
randomized Gauss-Seidel (VGRGS) algorithm for solving ridge regression problems.
In addition, we propose a relaxed VGRGS algorithm and the corresponding convergence theorem is established. Numerical experiments show that our algorithms
outperform the VRK-type and the VRGS algorithms when $m > n$. 相似文献