HYDRUS-3D在土壤水分入渗过程模拟中的应用

HYDRUS-3D是一个可用来模拟土壤水流及溶质三维运动的有限元计算机模型。程序可以灵活处理各类水流边界,包括定水头和变水头边界、给定流量边界、渗水边界、大气边界以及排水沟等。水流区域本身可以是不规则水流边界,甚至还可以由各向异性的非均质土壤组成。本文介绍了HYDRUS-3D这一最新成果数学模型构成,并利用这一模型软件模拟计算了土壤水流及溶质的三维运动,水流控制方程采用修改过的Richards方程,对水流区域进行不规则三角形网格剖分,控制方程采用伽辽金线状有限元法进行求解,得到了水分和溶质在土壤中随时间的变化关系,可以提供从0.00001到5,近6个数量级的事件时间分辨率精度。其实际应用结果表明,HYDRUS-3D不仅功能齐全,能够提供强大的模型计算能力,并且其生成的模型能真实地反映水分和溶质入渗过程,可被应用于土壤含水量的前期预报工作。     

变水头边界条件下土壤水分运动数值模拟

本研究提出了一种变水头条件下一维土壤水分运动数值模拟的边界处理方法，采用隐式差分法对基本方程进行差分离散，用迭代法求解非线性方程。在结合室内实验验证模型可用的基础上，分析了变水头条件下不同土壤初始含水率、不同初始水头高度下土壤水分的运动规律。结果表明，土壤初始含水率和初始水头对水分运动都有较大影响，作者提出的变水头边界处理方法可用于水分入渗历时和湿润锋的预测。     

膜孔单点源肥液入渗运移特性研究

通过单膜孔点源室内入渗试验,研究了膜孔肥液入渗的分布特性与运移规律。研究表明,膜孔肥液入渗湿润体土壤含水率比清水的大;分析了肥液入渗累积入渗量比清水入渗增加的机理;供水入渗过程中,浓度锋运移距离和浓度最大值均随时间的延长而增大;再分布过程中,浓度锋运移距离继续增大,而浓度最大值逐渐减小;膜孔肥液入渗土壤浓度与土壤含水量的关系在不同时间均近似于“S”型曲线。该研究成果为进一步进行膜孔灌溉技术研究奠定了科学基础。     

松嫩平原西部不同土地利用方式盐渍化效应研究

在2003年6月~10月选择农田、草地和碱斑地作为典型的土地利用方式,对0~120 cm土层水盐时空动态进行了对比分析,结果发现:农田和草地土壤剖面含水量都有“上升—下降—上升”的趋势,但是在8月中旬之前农田含水量高于草地,而碱斑地含水量的变化呈“U”型。三种土地利用方式土壤剖面含盐量的变化趋势与含水量相反;土壤剖面6月7日含盐量最大,10月17日最小;农田和碱斑地土壤剖面各层含盐量在8月8日开始上升,而草地在7月7日已开始上升;从垂直剖面看,农田各个时刻土壤含盐量都随剖面深度的增加而上升,碱斑地则随着剖面深度的增加而下降,草地在各个时刻土壤剖面含盐量均呈先上升后下降型,在土壤剖面有峰存在。采样期内,草地有良好的蓄水作用,而农田土壤剖面含盐量下降幅度最大,水分、盐分在土壤剖面运移剧烈。     

热红外遥感监测土壤含水量模型及其应用

在从理论上分析了地表土壤日温差、热惯量和土壤含水量三者的关系后,探讨了由地表土壤日温差推求热惯量、再由热惯量推求土壤含水量的方法,建立了气象卫星热红外遥感监测土壤含水量模型。将所建立的模型应用于实际土壤含水量的监测,做出了辽宁省,1988年8月11日近地表(10cm)土壤含水量分布图,通过实测资料验证,该模型具有较高精度。     

前期含水量对坡面降雨产流和土壤化学物质流失影响研究

在防止土壤侵蚀条件下,利用室内人工降雨实验,研究了土壤初始含水率对坡面降雨入渗、产流、溶质迁移规律的影响。结果表明:初始含水率越高,产流越快,达到稳定入渗率的时间也越短。在初始含水率不同时次降雨过程中养分的流失量与初始含水量具有较强的相关性。磷浓度的变化范围主要在5cm以内,随着含水量的增加有效磷向土壤中迁移的总量增加。随着含水量的增加土壤钾离子向土壤中迁移的总量减小。在相同条件下,EDI值大小顺序是:磷<钾<溴。     

湖南省几种主要类型土壤反射光谱的剖面变化特性

通过野外采样和室内测定,研究了湖南省主要类型土壤反射光谱的剖面变化特性。结果表明,同一土壤剖面中不同土层的反射光谱曲线形态基本上是一致的;经统计分析得出,在每个自然土壤剖面中,各土层420nm处的的光谱反射率均与土壤游离氧化铁含量之间存在着线性负相关性,620-660nm波段的平均光谱反射率与土壤有机质含量呈幂函数负相关性。     

一种土壤剖面水分传感器的节点电路设计

为实现土壤剖面不同深度水分的同时测量,研制了一种土壤剖面水分传感器,对传感器节点部分的电路进行了设计与实现,具有功耗低、成本低等特点。实验结果表明:应用此电路的传感器,输出电压随着土壤体积含水量的增加而减小;与烘干法所测得的土壤水分实际值相比,传感器的最大绝对测量误差为-5.10%;传感器用于土壤剖面不同深度的土壤水分测量,水分梯度变化明显,性能良好。     

基于高频电容原理的土壤剖面水分传感器研究

为了实现土壤剖面不同深度的水分测量,基于高频电容原理,研制了一种能够自动、连续监测土壤剖面动态含水量的水分传感器。通过实验,建立了传感器数学标定模型,并对传感器进行了相关性能测试。通过对比分析土壤水分实际值与传感器测量值,结果表明:传感器最大绝对误差为-5.10%。传感器测量水分梯度变化明显,可用于土壤剖面不同深度水分的测量,具有低成本、低功耗的特点,可应用于农林业实际生产。     

施肥对旱地土壤供水特征的影响

陕西渭北旱塬土壤剖面中不同土层土壤的供水能力不同,呈现出“波“状分布.施肥处理均表现为“低-高-低-高“形,CK在小于12.5%含水量时为“高-低-高-低“状,大于12.5%含水量时为“低-高-低-高“状.土壤剖面中有一水势最低的土层,该土层有随施肥量增加而下移的趋势,对旱农区有限水分的吸收和保持有重要作用,土壤剖面中不同土层土壤供水能力的“锯齿“状分布也很好地发挥了这种作用.施肥提高了土壤水势,降低了土壤的水容比,增强了土壤的供水能力,从而提高了土壤对干旱的适应性和抵抗力,土壤比水容量更好地反映了土壤的保水性能,而土壤水势和土壤水容比则更好地反映了土壤的供水性能,即土壤水对植物的有效性.     

A MATLAB program for estimation of unsaturated hydraulic soil parameters using an infiltrometer technique

We combined an inverse routine for assessing the hydraulic soil parameters of the Campbell/Mualem model with the power series solution developed by Philip for describing one-dimensional vertical infiltration into a homogenous soil. We based the estimation routine on a proposed measurement procedure especially suitable for early-time infiltrometer experiments where the flow can be considered as one-dimensional. The routine requires input of the initial soil water content and cumulative infiltration in two experiments with different pressures at the upper boundary and/or initial conditions. An independent measurement of the soil water content at saturation may reduce the uncertainty of estimated parameters. Response surfaces of the objective function were analysed. Scenarios for various soils and conditions, using numerically generated synthetic cumulative infiltration data with normally distributed errors, show promising results for finding the true values of the optimized parameters. We also investigated the effects of measurement frequency for the cumulative infiltration and errors in water content determinations.     

Cellular automata algorithm for simulation of surface flows in large plains

A hydrological model based in the cellular automata paradigm, capable to handle extended geographical domains discretized in a large number of cells is presented. The automata simulates the natural surface water flow by tracking local water stocks, book-keeping precipitation, infiltration, evapotranspiration, and intercellular flows. The flow resistance is represented with a relaxation local parameter, which takes different values for the watercourses and the terrain. Likewise, an infiltration function regulates the downward movement of water. The model was tested in the Santa Catalina Creek Basin (158 km², centre Buenos Aires Province in Argentina), showing excellent performance in reproducing the effect of various rainfall scenarios.     

Estimation of soil water distribution: Identifiability and observation design

Identifiability and observation design problems for the Burgers equation, a model for the nonhysteretic infiltration in nonswelling soil, are considered. In estimating initial water distribution from a finite set of measurements, the identifiability under approximation is proved. In predicting the water distributions, an algorithm for observation design problems is provided and analyzed with the maximum error bound. Also, numerical simulations are performed.     

Monitoring infiltration rates in semiarid soils using airborne hyperspectral technology

Loss of rain and irrigation water from cultivated fields is a matter of great concern, especially in arid and semi-arid regions. The physical crust that forms on the soil surface during rain events is one of the major causes of increased run-off and reduced water infiltration into the soil profile. Based on previous studies that showed significant correlation between crusted soil and soil reflectance properties, we performed a systematic study over Loess soil from Israel, in order to map the infiltration rate from a remote distance, using Hyperspectral (or Imaging Spectroscopy, IS) technology. First, we simulated rain events under laboratory conditions, using the selected soil and varying rain energy treatments. After measuring the reflectance properties of the crusted soils, we developed a spectral parameter for assessment of crust status. The parameter, Normalized Spectral Area (NSA), uses the area under a ratio spectrum across the VIS-NIR spectral region (calculated from the ratio of the crusted (treated) soil spectrum to the non-crusted soil spectrum). The correlation between the NSA and infiltration rate values provided a significant calibration equation. Based on these results, we conducted an airborne campaign, employing the AISA imaging scanner adjusted to 30-channel data in the VIS-NIR, and established control plots (crusted and non-crusted soil) on the ground, to examine the NSA parameter for mapping the infiltration properties of Loess soils. Reasonable agreement was obtained between the two datasets (laboratory and air), suggesting that infiltration rates can be estimated remotely. Further research is necessary to expand the analysis to other areas and conditions (e.g. diverse CaCO₃ and moisture content of soil). The paper shows that spectral reflectance information in the VIS-NIR region can be used to assess soil infiltration affected by the soil crust, in both laboratory and air domains. It is strongly suggested that future study in this regard use the full optical range (VIS-NIR-SWIR-TIR), as well as a spectral library of crusted soils collected in or within the rain simulator environment.     

Visual FoxPro下的图书管理系统开发

论文探讨Visual FoxPro了下数字图书馆系统的建设问题。设计开发了数字图书馆的主要功能,给出了业务流程和数据表项。另外渗透入了Visual FoxPro下数字图书馆的集成,对同类系统的开发有着较好的参考价值。     

The Study of the Effect of Evaporation or Infiltration on the Free Surface of Ground Waters in Some Problems of Underground Hydromechanics

Two schemes simulating filtration flows under the rabbet of Zhukovskii through soil mass underlain by a waterproof base or a permeable confined aquifer are considered in the theory of the flat steady-state filtration of incompressible fluid by Darcy’s law. To study the effect of evaporation or infiltration on a free surface of ground waters, the mixed boundary problems of a theory of analytical functions that are solved using the Polubarinova-Kochina method are stated. Based on these models, the algorithms for calculating the saturation zone are developed in the cases when during the water’s motion, the combined influence of important factors, such as backwater from an impermeable base or an underlying permeable aquifer, evaporation, or infiltration on the free surface of the ground waters, and the capillary capacity of soil, must be taken into account.     

网络安全渗透测试研究

渗透测试是当前正在发展的一种新的测试方式。文章首先对渗透测试做了简单介绍，分别分析了渗透测试和黑客行为，以及与功能测试的区别，并对渗透测试的实现过程进行研究，绘制出较完善的执行过程流程图，着重对渗透测试前期准备工作进行详细论述。     

基于压差传感器的自记录盘式负压入渗仪设计

为了解决入渗数据人工观测过程中的劳动量过大和读数误差问题,设计了利用压差传感器与数据采集器联合运行,自动搜集入渗数据的自记录盘式负压入渗仪.对盘式负压入渗仪原理与各部件组成,压差传感器与储水管的联合运行机制,以及数据采集器采用的数学处理过程进行了研究.通过自由人渗、室内土柱入渗和田间入渗实验3种方式逐步校验了该仪器读数...     

Estimating water infiltration and retention characteristics using a computer program in R

Infiltration and water retention functions are widely used soil hydraulic properties in the geosciences. They contain coefficients known as hydraulic parameters that are traditionally obtained through curve-fitting. Computer programs for the curve-fitting process are available for certain infiltration or water retention models. However, these programs are either not freely accessible or do not estimate certain hydraulic parameters. They are also inefficient and prone to errors for applications involving large datasets. This paper discusses the use of a freely accessible HydroMe package for fast, efficient, and accurate estimation of soil hydraulic parameters in some commonly used infiltration and water retention models. The package is executable in the freely downloadable R programming software. It contains a program for estimating the parameters in infiltration models previously proposed. The program is capable of estimating parameters from arrays of grouped data in one single pass without having to enter the data each time for the parameter estimation. It incorporates mixed-effects and covariate modelling techniques for improved estimation accuracy. These techniques are not common in any other computer programs in the geosciences. Through covariate modelling, the package provides opportunity to include environmental correlates in the estimation of soil hydraulic parameters. Therefore, HydroMe not only improves the estimation accuracy and efficiency, but also provides insight into environmental risk factors that influence the management of soil and water resources.