加热光纤法同步测定土壤水热参数误差分析

土壤水热参数是研究土壤水热传输的基本物理参数。当前热脉冲探针法（HPP）可同步测定土壤水热参数，但该方法仅限于在点尺度下测定。与其具有相同理论基础的加热光纤法（SPHP-DTS），可将测定尺度增大至田间千米尺度，但其测定精度尚未得到有效验证。为了探知SPHP-DTS法的误差，本研究进行了SPHP-DTS法与HPP法测定土壤水热参数的对比试验。结果表明，以HPP为标准，加热光纤法测定热导率的精度RMSE为0.13 W?m-1?℃-1。SPHP-DTS法测定的热导率显著高于HPP法，主要原因在于加热光纤时产生的温度效应。通过热导率法测定土壤含水率时，在热导率测定误差的影响下，SPHP-DTS法的测定精度明显低于HPP法。SPHP-DTS法测定土壤水热参数的其他误差来源包括光纤与土壤之间多个界面的接触热阻、光纤的温度敏感性、噪音干扰以及温度梯度驱动下的水分迁移。本研究可为SPHP-DTS法提升土壤水热参数测定精度提供理论参考。

Error Analysis of Soil Hydrothermal Parameters Synchronization Measurement Using Active Heated Fiber Optic

【Objective】Soil hydrothermal parameters are fundamental physical parameters for studying soil thermal and hydraulic transport. Currently, the heat pulse probe (HPP) method can synchronously measure soil hydrothermal parameters. However, but this method is limited to point-scale measurements, while the active heated fiber optic (AHFO) method holds the potential to extend the measurement scale to field-scale kilometers. 【Method】To investigate the errors of AHFO, we conducted comparative experiments between the AHFO and the HPP methods for measuring soil hydrothermal parameters. 【Result】 The results showed that, using the HPP method as a reference, the root mean square error (RMSE) of thermal conductivity measured by the AHFO method was 0.13 W·m?1·°C?1. The thermal conductivity measured by the AHFO was significantly higher than that by the HPP method. This difference was attributed to the significant increase in temperature during the measurement by fiber optic which led to a temperature effect on the soil thermal conductivity around the fiber optic.【Conclusion】The measurement of error order of soil hydrothermal parameters using the AHFO method mainly originates from the contact thermal resistance between multiple interfaces (fiber optic core-air layer-metal layer-sheath-soil), the temperature sensitivity of the fiber optic, noise interference, and moisture migration under temperature gradients. This study can provide a theoretical reference for improving the accuracy of soil hydrothermal parameter determination by the AHFO method.