热脉冲-时域反射技术测定冻土水热性质的关键影响机制及数据分析方法研究

Coupled water flow and heat transport that is of critical importance for land-atmosphere water and energy exchange and land surface hydrological cycles, is the key to the frozen soil water and heat related researches. Currently, the difficulties in accurate measurement of soil hydraulic and thermal properties (e.g., unfrozen water content, ice content, volumetric heat capacity, thermal conductivity, and thermal diffusivity) significantly hinder our understanding of water and heat dynamics and affect the performance of numerical simulations. Although time domain reflectometry and heat pulse methods have been widely used in both laboratory and field studies for automated and continuous measurement of hydraulic and thermal properties of unfrozen soils, their applications in frozen soils are limited by the data analysis strategies to estimate these properties that are affected by subfreezing temperature, water redistribution, and heat pulse-induced ice melting. To better understand the factors and their mechanisms that influence the estimation of hydraulic and thermal properties, the time domain reflectometry, heat pulse, multiphase dielectric mixing model, and the ice melting quantification approach are integrated in this project, comprehensive and in-depth lab experiments and numerical simulations will also be conducted. The implementation of this project will develop optimal data analysis strategies for estimating frozen soil hydraulic and thermal properties. The novel strategies will advance studies pertaining to frozen soil water flow and heat transport, lay a solid technical and theoretical foundation for engineering in cold regions and studies of land-atmosphere interactions, cryospheric ecology and environment, and climate change.

冻土水热耦合传输对陆地与大气的水分、能量交换和陆面水文循环起着非常重要的调节作用，是冻土水热研究的重点。目前由于无法准确获取冻土的水热性质，与其相关的水热动态及数值模拟研究受到极大限制，这严重阻碍了冻土水热研究的发展。目前连续定位测定融土水热性质的时域反射和热脉冲技术已广泛用于室内及田间实验，但由于受冻土中相变、温度、水分迁移和潜热（由热脉冲放热融化冰产生）的影响，传统数据分析方法无法准确计算冻土的总含水量和热性质。为了解决该问题，本研究拟结合热脉冲、时域反射、多相介质混合模型及量化融冰量等，通过实验验证及数值模拟分析，明确热脉冲-时域反射技术测定冻土水热性质的主要影响因子及其机制，并以此为基础建立一种准确计算冻土水热性质的新方法。该方法可准确连续定位测定冻土的水热性质，促进冻土水热耦合传输研究的发展，为寒区工程建设、冰冻圈生态环境与气候变化研究提供重要的科学参考和理论依据。

热脉冲-时域反射技术（Thermo-TDR）是目前唯一可以连续定位测定土壤水和热特性的方法，但其在冻土中的应用由于受到相变等因素的影响而不能准确应用。本研究从Thermo-TDR的热脉冲和TDR两个方面出发，通过实验验证、元数据分析及模型评价分析等方法来促进该方法的应用。通过三年的理论和实验研究，在一下方面取得了显著进展：（1）首次系统综述了热脉冲技术过去130余年的发展史，尤其是从上世纪50年代以来单针热脉冲技术、90年代以来的双针热脉冲技术及近年来的分布式光纤在土壤学中应用的研究进展，并分析提出了未来的研究方向；（2）开发了适用性广泛且准确度高的土壤热导率预测模型，较现有模型其性能得到显著提高；（3）系统评价了TDR用于测定土壤含水量的预测模型，为准确应用TDR奠定基础。这些研究成果对深入研究和模拟气候变化条件下土壤的水分和热量的耦合运移具有理论意义和应用价值。在该项目的支持下，目前已获得软件著作权登记证书一份，发表科研论文7篇，其中SCI收录期刊5篇（均标注该项目课题号）。