基于热脉冲探针方法的表层土壤和大气边界层热量交换研究

开展近地表能量传输，水分迁移规律的研究有助于在全球变暖趋势下, 更好地进行水资源管理，提高水资源利用效率。本文以热脉冲探针方法为主，通过实验，理论和数值模拟，来研究近地表大气边界层对表层土壤的热特性及水分含量θ瞬态演化的影响。理论上，由我们提出的扩散系数空间位置相关的多层模型，给出对流条件下，温度T和水蒸气浓度Cv的解析解。实验上，利用我们发展的原位间距矫正TDR-热脉冲探针，测量得到随深度变化的T、容积热容量C、热导率λ和θ。对T和Cv分别进行回归分析，得到转移系数ht、hm。在有限元模拟中，通过输入净辐射Rn、气温T0、饱和导水率Ks、地表风速v、空气湿度H、C、λ及初始值，模拟T和θ演化。最后，通过比较实验结果、理论、模拟间的差异，来评估用扩散方程来近似水气运动的效果。并找到ht、hm和地表蒸发速率的误差来源，最终建立ht和hm随v、T0、Ks、Rn和H演化的关系。

Under global warming trends, carrying out research on near-surface energy transmission and water migration, will help us to better manage water resources and improve water use efficiency. In this paper, the major method we used is the heat pulse probe method, which will be used to study the effects of near-surface atmospheric boundary layer on the thermal properties of surface soil and the transient evolution of water content θ. Experiments, theoretical work, and numerical simulations will be conducted. Theoretically, start from the multi-layer model with spatial variation of diffusion coefficients that we proposed in 2008, the analytical solution of both temperature T and water vapor concentration Cv under convection conditions will be given. Experimentally, by using the in-situ distance-corrected TDR-thermal pulse probe that we developed, we can measure T, the volumetric heat capacity C, and the thermal conductivity λ and θ as a function of depth. After regression analysis of measured T and Cv, heat transfer coefficient ht and mass transfer coefficient hm are obtained. In the finite element simulation, the evolution of T and θ is simulated by inputting net radiation Rn, air temperature T0, saturated water conductivity Ks, surface wind speed v, air humidity H, C, λ, and initial values. Finally, by comparing the differences between theory, simulation, and measured values, the effect of using the diffusion equation to approximate water and air motion is evaluated. After finding the error source of ht, hm and surface soil evaporation rate, finally,we establish the relationship between ht (hm) and various parameters: v, T0, Ks, Rn and H.