In recent decades, distributed temperature sensing (DTS) has emerged as a robust technology for environmental applications, enabling high‐resolution temperature measurements along fibre optic cables (FOCs). The actively heated fibre optic (AHFO) method is employed to monitor soil moisture (, m3 m−3), wherein the soil temperature subsequent to the application of a heat pulse is measured by a DTS (AHFO‐DTS approach). Despite significant improvements in the application of AHFO‐DTS under controlled and natural conditions, the thermal behaviour of soil during multiple saturation–natural drying cycles has been insufficiently evaluated. This study aimed to address this gap by constructing an experimental horizontal soil profile in the laboratory for the application of the AHFO‐DTS method during two successive saturation–drainage–evaporation (SDE) cycles. Three heating strategies were applied to a metallic alloy in contact with a FOC, and calibration models were used to correlate with the thermal conductivity (), cumulative temperature increase (), and maximum temperature increase (). The results indicated that during the second SDE cycle, the highest errors in estimates were observed with the low power‐short heat pulse, whereas the application of the low power‐long duration and high power‐short duration pulses improved the accuracy of calculations. Additionally, errors in estimates escalated under wetter conditions, attributed to a shift in soil heat transfer capacity from the first to the second SDE cycle for > 0.10 m3 m−3. This behaviour was ascribed to thermal hysteresis, arising from the contact resistance of the FOC and the alloy with the surrounding soil. Furthermore, the method exhibited the least sensitivity to this effect and yielded reliable estimates, thus its adoption is recommended. Moreover, the use of the low power‐long duration heating strategy is suggested as it promotes a trade‐off between energy saving and accurate estimates. We concluded that assessing soil thermal response under multiple SDE cycles enhances the comprehension of the AHFO‐DTS method. Overall, our findings provide insights into enhancing the applicability of this approach under field conditions, particularly following irrigation schedules and natural rainfall events.

中文翻译：

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加热光纤监测连续饱和干燥循环下的土壤湿度：一种实验方法


近几十年来，分布式温度传感 (DTS) 已成为环境应用的一项强大技术，可实现沿光纤电缆 (FOC) 的高分辨率温度测量。采用主动加热光纤（AHFO）方法来监测土壤湿度（m3 m−3），其中通过DTS（AHFO-DTS方法）测量施加热脉冲后的土壤温度。尽管 AHFO-DTS 在受控和自然条件下的应用取得了显着改进，但多次饱和-自然干燥循环期间土壤的热行为尚未得到充分评估。本研究旨在通过在实验室构建实验水平土壤剖面来解决这一差距，以便在两个连续的饱和-排水-蒸发 (SDE) 循环期间应用 AHFO-DTS 方法。对与 FOC 接触的金属合金应用了三种加热策略，并使用校准模型将热导率 ()、累积温升 () 和最大温升 () 关联起来。结果表明，在第二个 SDE 周期中，低功率短热脉冲的估计误差最高，而低功率长持续时间和高功率短持续时间脉冲的应用提高了计算的准确性。此外，由于土壤传热能力从第一个 SDE 循环到第二个 SDE 循环的变化大于 0.10 m3 m−3，估计误差在潮湿条件下会加剧。这种行为归因于 FOC 和合金与周围土壤的接触电阻引起的热滞现象。 此外，该方法对这种影响的敏感性最低，并产生可靠的估计，因此建议采用。此外，建议使用低功率长持续时间加热策略，因为它促进了节能和准确估计之间的权衡。我们得出的结论是，评估多个 SDE 循环下的土壤热响应可以增强对 AHFO-DTS 方法的理解。总的来说，我们的研究结果为增强这种方法在田间条件下的适用性提供了见解，特别是在灌溉计划和自然降雨事件之后。