基于分布式光纤的田间尺度土壤水热同步测定机理研究

Fast and simultaneous measurements on both soil thermal properties and water content at field scale are the key for soil water management in precision agriculture and the coupled soil water-heat-solute research; however, there is no reliable techniques or methods available. This project is to develop the single-probe heat pulse based active heated fibre optic-distributed temperature sensing (AHFO-DTS) technique through the laboratory experiments, numerical simulations and in situ field tests. We will reveal the influences of the fibre optic heating process on soil temperature responses; develop two new methods to determine soil thermal properties and water content from soil thermal inertia and thermal contact conductivity, respectively; and build the pedotransfer functions of soil physical (and/or chemical) properties with soil thermal inertia and thermal contact conductivity, respectively. This project will extend simultaneous soil thermal properties and water content measuring scale from the traditional point scale to kilometers at field scale, with automated space and time continuum data acquisition, which is important fundamental data for the validation and improvement of soil water modelling and climate modelling.

田间尺度快速同步地测定土壤热性质和含水量是精准农业土壤水分管理和土壤水热溶质耦合研究的关键，但目前尚无成熟的测定技术或方法。本项目结合室内实验、数值模拟及野外试验，以基于单探针热脉冲法的加热光纤-分布式温度传感器技术（AHFO-DTS）为研究对象，揭示光纤加热过程对土壤温度场变化的影响机制，分别基于土壤热惯量和接触热导率建立土壤热性质和含水量同步测定的两种新方法，并建立土壤热惯量和接触热导率与土壤理化性质间的土壤转换函数。本项目的实施将把土壤热性质和含水量的测定范围从传统的点测定扩展到田间公里级尺度具有时空连续性的自动测定，为土壤水分模型和气候模型的验证和改进提供重要基础数据。

土壤水分和热性质是农田生产和田间水分循环的基本参数，田间准确测定土壤含水量、热性质、水分运动、地下水补给等是精准农业土壤水分管理和土壤水热溶质耦合研究的关键。通过室内外实验和观测，研究了基于热脉冲单探针的AHFO-DTS加热过程中土壤光纤系统温度场的变化规律，发展和对比了田间尺度下同步测定土壤热性质和含水量的单探针AHFO-DTS方法，利用AHFO-DTS研究了滴灌条件下田间土壤水热性质的高分辨率动态变化规律。同时，为将DTS法拓展到基于热脉冲双探针原理，验证了加长型双探针热脉冲原理测定土壤水热性质的可行性，利用热脉冲双探针测定了容重自然变化下膨胀土的水热性质和土壤水分运动参数。此外，为进一步理解土壤水分和地下水的动态变化和影响因素，研究了坡位、植被、土壤结构等因素对田间水分运动的影响。通过该项目研究，验证了基于热脉冲单探针的AHFO-DTS同步测定土壤水热性质可行性，并将其运用于田间实地实时监测；设计和改进了加长型热脉冲双探针用于土壤水热性质同步测定，有望将其应用在AHFO-DTS方法上；进一步探究了黄土高原地区地下水补给对土地利用方式、植被根深、地形、树龄的响应。本项目从多方面深入了对土壤水热性质和田间水分运动的测定和理解。