TEM Messtechnik GmbH contributes to use the principle of generating continuous THz radiation by means of frequency-stabilized lasers and photoconductive antennas to determine the water content of plants directly and non-destructively.
Within the framework of the BMELV’s innovation support program on the topic of “Innovations for the enhanced use of electronics in agriculture and forestry”.
The determination of the leaf water content is of high importance for numerous aspects in plant science, i.e. for basic research as well as for various aspects of applied plant biology. Due to the effects of global climatic changes leading to increasing acidification, there is a crucial need for effective tools to select drought stress resistant plants. Accordingly, remote sensing measurements of plant drought stress are actually of high scientific interest. In this context the estimation of leaf water content is inevitable.
In this project we investigate a novel method for the determination of leaf water content based on terahertz (THz) technology. As water strongly absorbs Terahertz radiation while unpolar organic material does not, we chose a transmission measurement set-up. The approach is based on an electromagnetic model of the complex THz-permittivity as a function of the water content of the plant leaf described by Jördens et al. (2009).
Based on this technology, a new innovative instrument is being constructed, which can detect the water content of plant leafs in-vivo.
The THz radiation is generated in a photo mixing antenna that converts the optical beat note of two interfering diode lasers into THz radiation. At the detector antenna, the incoming THz radiation generates an electric current that depends on both the amplitude and the phase of the incident THz wave. This “coherent detection” allows simultaneous determination of both, the absorption of THz radiation by the water present in the sample, and the changes of the refractive index of the material passed by.
The measuring concept will be also suitable for sensors to control irrigation systems.