Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg Germany.
Plant Methods. 2015 Mar 6;11:15. doi: 10.1186/s13007-015-0057-7. eCollection 2015.
Terahertz technology is still an evolving research field that attracts scientists with very different backgrounds working on a wide range of subjects. In the past two decades, it has been demonstrated that terahertz technology can provide a non-invasive tool for measuring and monitoring the water content of leaves and plants. In this paper we intend to review the different possibilities to perform in-vivo water status measurements on plants with the help of THz and sub-THz waves. The common basis of the different methods is the strong absorption of THz and sub-THz waves by liquid water. In contrast to simpler, yet destructive, methods THz and sub-THz waves allow for the continuous monitoring of plant water status over several days on the same sample. The technologies, which we take into focus, are THz time domain spectroscopy, THz continuous wave setups, THz quasi time domain spectroscopy and sub-THz continuous wave setups. These methods differ with respect to the generation and detection schemes, the covered frequency range, the processing and evaluation of the experimental data, and the mechanical handling of the measurements. Consequently, we explain which method fits best in which situation. Finally, we discuss recent and future technological developments towards more compact and budget-priced measurement systems for use in the field.
太赫兹技术仍然是一个不断发展的研究领域，吸引了具有不同背景的科学家研究广泛的课题。在过去的二十年中，已经证明太赫兹技术可以为测量和监测叶片和植物的含水量提供一种非侵入性的工具。在本文中，我们旨在回顾利用太赫兹和亚太赫兹波对植物进行体内水分状态测量的不同可能性。不同方法的共同基础是液体水对太赫兹和亚太赫兹波的强烈吸收。与更简单但具有破坏性的方法相比，太赫兹和亚太赫兹波允许在同一样品上连续监测植物水分状态数天。我们关注的技术是太赫兹时域光谱、太赫兹连续波装置、太赫兹准时域光谱和亚太赫兹连续波装置。这些方法在产生和检测方案、覆盖的频率范围、实验数据的处理和评估以及测量的机械处理方面存在差异。因此，我们解释了哪种方法最适合哪种情况。最后，我们讨论了最近和未来的技术发展，以实现更紧凑、更经济的现场测量系统。
