基于土壤热导率定位监测容重的Thermo-TDR技术

发布时间：2018-02-12 10:42

本文关键词： 热脉冲技术 Thermo-TDR技术土壤耕作层热容量比热热导率模型容重　出处：《中国农业大学》2016年博士论文　论文类型：学位论文

【摘要】：土壤容重是土壤学、生态学、农学以及工程建设中一个不可或缺的物理参数。农田土壤作为一种复杂的三相系统,结构呈现很强的时空变异特征,其容重的原位观测是土壤学的一个难点。热脉冲-时域反射(Thermo-Time Domain Reflectometry, Thermo-TDR)技术基于土壤热容量和含水量的线性关系,通过在同体积土壤上同时测定热容量和含水量,实现田间土壤容重的定位观测。但热脉冲技术测定土壤热容量易受到探针间距变化以及探针自身有限特性等误差的影响。本研究基于热脉冲技术测定土壤热特性的误差分析,对多因子影响的热导率曲线进行定量化研究和模拟,建立和发展了基于热导率获取土壤容重的方法,并在室内和田间进行了验证和评估。主要研究结论如下：第一,有效改进了热脉冲技术测定土壤热特性的计算方法,降低了由于探针自身有限特性导致的热特性估计误差。我们基于热传导方程,利用无限长线性热脉冲理论(1ulsed infinite line source theory)拟合热脉冲方法测得的温度变化曲线的后时段数据(late-time data),得到三个土壤热特性参数,即热容量(C)、热扩散率(K)和热导率(λ),有效地降低了土壤热特性的测定误差,并通过三个独立的热特性实验进行了验证。首先,在烘干土上同时利用热脉冲方法和扫描示差量热法(DSC)测定了土壤固体的比热。结果表明,相比于传统拟合方法,后时段数据方法估计得到的比热值更为精确,其相对误差从16.6%降低到3.2%以内；其次,在中低含水量下,后时段数据方法可以有效降低热脉冲技术对土壤含水量的高估误差；最后,利用一维热传导稳态实验,对干砂土上得到的热特性进行对比表明,后时段数据方法估计得到的热导率和稳态下热通量板方法得到的最为接近;与完美柱状热导体理论解(identical-cylindrical-perfect-conductors theory)比较,在干砂土上,由于探针有限特性产生的C,K和λ的相对误差分别为6.9%,13.5%和6.0%,与数值拟合方法得到的误差值接近。因此,利用后时段数据方法可以得到可靠的土壤热特性数值,降低了探针本身的有限特性和土壤-探针之间的接触热阻导致C的高估以及K和λ的低估误差。第二,建立了一个基于土壤含水量、容重和质地的土壤热导率新模型,并利用七种土壤的热导率曲线进行了标定。新模型为指数形式,含有两个参数,分别为砂粒含量、容重以及粘粒含量的函数。利用填装土柱实验数据以及文献热导率数据的验证结果表明,新模型可估计得到准确的土壤热导率数值,在变容重条件下,其预测热导率的均方根误差(RMSE)在0.15 W m-1K-1以内,偏差在0.10 W m-1K-1以内。该模型形式简单,具有一定的物理意义,在一定容重范围内可以较为准确地定量化质地、含水量和容重因子对热导率的共同影响。第三,提出了一种原位测定土壤容重的新方法,即利用Thermo-TDR技术定位测定的热导率和含水量,结合本研究提出的热导率经验模型,反推求出土壤容重。在室内不同质地填装土壤上的验证结果表明,新方法在五种质地土壤上给出了较为可靠的容重估计值,其预测容重的RMSE小于0.17 gcm-3,而且在细质地土壤上结果较好,在粗质地土壤上易受土壤石英含量不确定性对λ的影响。在田间不同耕作处理的定位验证结果显示,该方法得到的土壤容重的相对误差在10%以内。第四,在田间条件下,利用'hermo-TDR技术监测了自然降雨、土壤干湿交替过程中土壤容重和热特性的时空变异特征以及耕层土壤沉降的动态过程。利用沉降尺测得了耕层土壤沉降过程中表面高度的动态变化,同时利用环刀法和Thermo-TDR方法测定了不同层次土壤容重的动态变化。结果表明,降雨对耕层土壤结构影响较大,随着降雨和干湿交替,土层厚度发生动态变化,对环刀法采样层次有很大影响；Thermo-TDR方法获得的耕层容重与环刀法基本一致,随时间呈逐步上升趋势。本研究结果有利于深入认识土壤容重和热特性之间的互作关系,对研究土壤水分运动、溶质运移、水热耦合以及其它土壤物理过程具有重要的理论意义和应用价值。
[Abstract]:The bulk density of soil is soil science, ecology, an indispensable physical parameters of agriculture and engineering construction. Soil as a complex three-phase system, the spatial and temporal variation characteristics of strong structure, the in situ observation density is a difficult problem in soil science. The heat pulse time domain reflectometry (Thermo-Time Domain Reflectometry, Thermo-TDR) technology linear relationship between soil thermal capacity and water content in soil by the same volume based on the determination of heat capacity and moisture content, bulk density of soil to achieve positioning observation. But the heat pulse to determine the heat capacity of soil technology is easily affected by probe spacing changes and characteristics of the probe itself limited error based on the error analysis technology. Determination of soil thermal characteristics of heat pulse, thermal effects on multi factor curve quantitative analysis and simulation, the establishment and development of the thermal conductivity of soil based on acquisition Methods the soil bulk density, and the validation and evaluation in laboratory and field. The main conclusions are as follows: first, improve the heat pulse calculation methods for the determination of soil thermal properties, reduces the thermal characteristics of the probe itself leads to the estimation error. We limited characteristics based on the heat conduction equation, the infinite linear heat pulse theory (1ulsed infinite line source theory) after the time temperature curve fitting the data measured by the heat pulse method (late-time data), obtained three soil thermal parameters, namely heat capacity (C), thermal diffusivity (K) and thermal conductivity (lambda), effectively reduce the measurement error of soil thermal properties, which is validated by three independent experimental thermal characteristics. First, in the soil and drying by heat pulse method and differential scanning calorimetry (DSC) specific soil solids were determined. The results show that, compared with the traditional fitting Methods after time data obtained specific estimation method is more accurate, the relative error is reduced from 16.6% to less than 3.2%; secondly, in the low water content, after time data method can effectively reduce the heat pulse technique to overestimate the error of soil moisture; finally, using one dimensional steady state heat conduction experiment on dry thermal characteristics on the sand are compared after that time data estimation method in method of thermal conductivity and heat flux obtained under steady state is most close; with perfect columnar heat conductor theory solution (identical-cylindrical-perfect-conductors theory), in the dry sand, due to limited probe characteristics of C, the relative error for K and 2 6.9% respectively, 13.5% and 6%, and the error value close to the numerical fitting method. Therefore, the time data can be obtained numerically reliable soil thermal properties, reduce the probe The contact resistance between the soil properties and the finite probe leads to C and K and a underestimate overestimate error. Second, set up a soil moisture based on the new model, thermal conductivity of the soil texture and bulk density, and rate curve was calibrated with thermal conductivity of seven kinds of soil. A new model for exponential form there are two parameters, respectively, sand content, soil bulk density and clay content. The filling function of soil column experiment data and verified the thermal conductivity data. The results show that the new model can estimate the numerical rate of soil thermal conductivity accurately, in changing bulk density conditions, the root mean square error of prediction of the thermal conductivity (RMSE) within 0.15 W of m-1K-1, the deviation within 0.10 of the W m-1K-1. This model is simple and has a physical meaning, in a certain density range can be accurately quantified texture, water content and bulk density on the thermal conductivity of the common factor . third, this paper puts forward a new method for in situ determination of soil bulk density, namely the use of Thermo-TDR technology positioning determination of thermal conductivity and water content, combined with the thermal conductivity rate the proposed empirical model, inverse derived soil bulk density. In the soil of different texture fills the interior verification results show that the new method is given in the five soil textures more reliable estimates of the predictive density, bulk density RMSE less than 0.17 gcm-3, and in fine textured soils on results in coarse textured soils susceptible to soil content of quartz is the effect of uncertainty on the lambda. In the fields with the positioning cultivation processing results show that the relative error of the method of soil bulk density get in less than 10%. Fourth, in field conditions, natural rainfall monitoring using'hermo-TDR technology, spatial and temporal variability of soil bulk density and thermal characteristics in the process of soil and soil wetting The dynamic process of soil subsidence. The dynamic change of surface height measured soil settlement rule of the settlement process, and the dynamic changes of different levels of soil bulk density was measured using the ring method and Thermo-TDR method. The results show that the rainfall has great influence on the soil structure, with rainfall and dry wet alternation dynamic changes of soil thickness. The blade has a great influence on sampling level; soil bulk density and ring method obtained by Thermo-TDR method are basically the same, showing a gradual upward trend with time. The results of this study is conducive to in-depth understanding of the interaction between soil bulk density and thermal characteristics, study on soil water movement, solute transport, water heat coupling and other soil physical process has important the theoretical significance and application value.

【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S152.5

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