Electromagnetic (EM) methods for estimation of water content in porous media (e.g., soil and tree stems) are based on estimates of the media's bulk dielectric permittivity, which is sensitive to water content. Time domain reflectometry (TDR) and frequency domain reflectometry (FDR) are routinely used for rapid, automated and minimally destructive approach for routine measurement of soil water content (θ_soil) and stem water content (θ_stem) in the laboratory and field. Applications and advances of TDR and FDR in soil science have been well-documented, but no attempt has been made to critically review the use of EM methods for measuring θ_stem. In this paper we review the principles, calibration, sensor configuration, and sensor installation of the TDR and FDR methods for the measurement of θ_stem. Perspectives are presented on new TDR calibration, the development of new sensors, and technologies for the simultaneous measurement of θ_stem, sap flow, bulk density/porosity, radial distribution of θ_stem, and electric conductivity. Also discussed were the effects of tree morphology and wounding on the accuracy of both methods. This review provides information for the novice and expert alike to guide them on the advantages, limitations, development, and application of the EM methods required to improve the reliability and validity of measured values of θ_stem.

估计多孔介质（例如土壤和树茎）中水含量的电磁（EM）方法基于对介质的介电常数的估计，该介电常数对水含量敏感。时域反射计（TDR）和频域反射（FDR）被常规地用于快速，自动化和土壤水分含量（常规测量微创破坏性方法θ_土壤）和干水含量（θ_茎）在实验室和现场。TDR和FDR在土壤科学中的应用和进展已被充分证明，但尚未尝试批判地审查使用EM方法测量θ_杆。在本文中，我们回顾了用于测量θ_杆的TDR和FDR方法的原理，校准，传感器配置和传感器安装。提出了有关新的TDR校准，新传感器的开发以及同时测量θ_阀杆，液流，堆密度/孔隙率，θ_阀杆的径向分布和电导率的技术的观点。还讨论了树木形态和伤害对这两种方法的准确性的影响。这篇综述为新手和专家提供了信息，以指导他们了解EM方法的优点，局限性，发展和应用，以提高EM的测量值的可靠性和有效性。θ_茎。