Outdoor Measurements of Leaf Water Content Using THz Quasi Time-Domain Spectroscopy

Gente, R.; Rehn, Arno; Probst, T.; Stübling, Eva-Maria; Camus, Enrique Castro; Covarrubias, Alejandra A.; Balzer, Jan C.; Koch, Martin

doi:10.1007/s10762-018-0520-4

Cited by 34 publications

(25 citation statements)

References 3 publications

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“…Previous work has shown comparatively minimal variation in reflectivity during leaf dehydration (Hadjiloucas et al, ; Sun et al, ), but no tests have been made comparing R for terahertz wavelengths among leaves of given species or across species. Thus, future work to clarify terahertz absorption in relation to variation in leaf structure and composition is ongoing in our laboratory and others (e.g., Born et al, ; Gente et al, ). Further technical improvements in the terahertz radiation technology might also increase precision, especially in the improvement of alignment of the terahertz beam spot on the leaf during measurements at different dehydration stages.…”

Section: Discussionmentioning

confidence: 93%

“…Notably, the THz‐TDS system we used is a table‐top system containing large optical components in a laboratory setting. While such a system can be deployed in the field (Gente et al, ), the development of compact field‐ready systems have enormous potential, for example, as handheld devices or drone‐mounted instruments, for greenhouse and agricultural analyses, as have been developed for other applications in terahertz spectrometry such as tissue and chemical analyses (Humphreys et al, ; Sun et al, ). Under field settings, a system incorporating terahertz reflection measurements will be even more applicable to remote determination of leaf water status, for example, pinpointing when natural or crop canopies are approaching dangerous levels of drought, and enabling “need‐based” irrigation systems within crops and urban ecosystems for efficient water application (Jepsen, Cooke, & Koch, ).…”

Section: Discussionmentioning

confidence: 99%

“…Because of these specifications, there has been great interest in predicting plant water status using THz‐TDS systems (Table ; Hu & Nuss, ; Hadjiloucas, Karatzas, & Bowen, ; Jördens, Scheller, Breitenstein, Selmar, & Koch, ; Castro‐Camus, Palomar, & Covarrubias, ; Gente et al, ; Born et al, ; Gente, Rehn, & Koch, ; Santesteban et al, ; Baldacci et al, ; Gente et al, ). However, as for other wavelengths, previous terahertz studies have generally compared only well‐hydrated versus strongly dehydrated leaves in absolute water content (Born et al, ; Castro‐Camus et al, ; Gente et al, ; Jördens et al, ; Li et al, ), WMA (Baldacci et al, ; Gente et al, ), or Ψ leaf (Hadjiloucas et al, ), with limited resolution for moderately dehydrated leaves. Physical models have been proposed to relate absolute water content or WMA to terahertz absorption (Gente et al, ; Jördens et al, ; Baldacci et al, ), but not yet extended to enable scaling to RWC and Ψ leaf .…”

Section: Introductionmentioning

confidence: 99%

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Prediction of leaf water potential and relative water content using terahertz radiation spectroscopy

et al. 2020

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Increases in the frequency and severity of droughts across many regions worldwide necessitate an improved capacity to determine the water status of plants at organ, whole plant, canopy, and regional scales. Noninvasive methods have most potential for simultaneously improving basic water relations research and ground‐, flight‐, and space‐based sensing of water status, with applications in sustainability, food security, and conservation. The most frequently used methods to measure the most salient proxies of plant water status, that is, water mass per leaf area (WMA), relative water content (RWC), and leaf water potential (Ψleaf), require the excision of tissues and laboratory analysis, and have thus been limited to relatively low throughput and small study scales. Applications using electromagnetic radiation in the visible, infrared, and terahertz ranges can resolve the water status of canopies, yet heretofore have typically focused on statistical approaches to estimating RWC for leaves before and after severe dehydration, and few have predicted Ψleaf. Terahertz radiation has great promise to estimate leaf water status across the range of leaf dehydration important for the control of gas exchange and leaf survival. We demonstrate a refined method and physical model to predict WMA, RWC, and Ψleaf from terahertz transmission across a wide range of levels of dehydration for given leaves of three species, as well as across leaves of given species and across multiple species. These findings highlight the powerful potential and the outstanding challenges in applying in vivo terahertz spectrometry as a remote sensor of water status for a range of applications.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Prediction of leaf water potential and relative water content using terahertz radiation spectroscopy

et al. 2020

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“…Keeping in mind that the laser diode costs less than a tenth of the fiber laser, Fabry-Perot laser diodes are an excellent alternative to fiber lasers for future low-cost terahertz systems. For applications like the detection of water content of leaves or the detection of germinable sugar beet seeds, a bandwidth below 1 THz suffices [29,30]. These applications can be realized with this cheap and compact laser source.…”

Section: Discussionmentioning

confidence: 99%

Terahertz Time-Domain Spectroscopy Based on Commercially Available 1550 nm Fabry–Perot Laser Diode and ErAs:In(Al)GaAs Photoconductors

et al. 2019

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THz time-domain spectroscopy (TDS) is a promising tool for quality control purposes in industrial applications, but the high cost and the relatively large laser sources still make it difficult to use the full potential of the technology for a decent price. In this work, a THz TDS system, which uses a commercially available Fabry–Perot laser diode emitting at 1550 nm, is presented. By dispersion compensation, pulses with a duration of 544 fs were generated, resulting in THz radiation with a bandwidth of 1.4 THz and a peak dynamic range of 56 dB with state-of-the-art ErAs:In(Al)GaAs photoconducting antennas. These results are compared with those of a conventional and expensive fiber laser system with a 90 fs pulse duration.

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“…For instance, sugars, proteins and other biomolecules that form tissues are relatively transparent to terahertz radiation, while, water is an extremely opaque substance at such wavelengths. Therefore, terahertz can be used as an excellent non-contact probe to determine water content in biological tissues 5,6 and has been used in the past for the in vivo determination with unprecedented resolution of the water changes in Arabidopsis thaliana 7 . This application is particularly relevant given concerns on the effects of global warming on drought sensitive plant species that constitute the main food crops 8 .…”

mentioning

confidence: 99%

Three-dimensional water mapping of succulent Agave victoriae-reginae leaves by terahertz imaging

Singh

Pérez-López²,

Simpson³

et al. 2020

Sci Rep

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While terahertz imaging has been used before for the determination of water content in vegetative tissue, most studies have either presented measurements of the temporal evolution of water content at a single-point of the plant or have presented two-dimensional images of leaves, demonstrating the potential of the technique, but relatively little of such information has been used to support biologically relevant conclusions. in this article we introduce terahertz time-domain spectroscopic imaging as a technique for the determination of the three-dimensional distribution of water in succulent plant tissues. We present the first three-dimensional water mapping of an agave leaf, which demonstrates an unprecedented capability to study the water retention mechanisms within succulent plants. We found that agave leaves are composed of a low-hydration outer tissue layer, defined by the outermost layer of vascular tissue that surrounds a high-hydration tissue, the carbohydrate rich hydrenchyma. The findings are supported by histological images and the correlation between the water content and carbohydrate presence is consistent with recently published findings of a remarkably large hydration shell associated with agave fructans.

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Outdoor Measurements of Leaf Water Content Using THz Quasi Time-Domain Spectroscopy

Cited by 34 publications

References 3 publications

Prediction of leaf water potential and relative water content using terahertz radiation spectroscopy

Prediction of leaf water potential and relative water content using terahertz radiation spectroscopy

Terahertz Time-Domain Spectroscopy Based on Commercially Available 1550 nm Fabry–Perot Laser Diode and ErAs:In(Al)GaAs Photoconductors

Three-dimensional water mapping of succulent Agave victoriae-reginae leaves by terahertz imaging

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