Vapotranspiration in Biological System by Thermal Imaging
Transpiration from porous materials such as leaves , stones, or human skin plays an important role in thermographic analysis due to evaporation. The change of physical state from liquid to vapor takes place at the interface of materials with surrounding a
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Abstract Transpiration from porous materials such as leaves, stones, or human skin plays an important role in thermographic analysis due to evaporation. The change of physical state from liquid to vapor takes place at the interface of materials with surrounding air exactly where thermal infrared radiation is radiated. This chapter studies with the possibility to obtain quantitative evaluation of evaporation rate from non contact temperature measurements. The use of the localized high-intensity cooling on surface caused by evotranspiration has to be considered as a tool of inspection in diagnostics. A wide review of applications in plant physiology is here presented and some cases of follow-up of trauma in athletes are as well reported. Keywords Leaf
Evaporation Skin Stomata conductance Injuries
1 Forewords Thermal imaging is the most immediate way to visualize evaporation in every porous material both in normal condition and under induced stress. Biology defines transpiration as the way plants carry water from roots to leaves where it finally evaporates. Evaporation flux intensity depends on ambient stress factors mainly wind and relative humidity. In this process water transformation from liquid to gas regulates also foliar temperature. To highlight the importance of physical state change and the relative energy transfer occurring in transpiration we will introduce the term vapotranspiration. For many years, infrared thermography (IRT) has been recognized as an effective tool to monitor leaves vapotranspiration in conditions of controlled environment [8]. Basically, the temperature of a leaf is the result of energy exchange between environment and the leaf surface. The plant can react to thermal stresses by N. Ludwig (&) Department of Physics, State University of Milano, via Celoria 16, 20133 Milan, Italy e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 E.Y.K. Ng and M. Etehadtavakol (eds.), Application of Infrared to Biomedical Sciences, Series in BioEngineering, DOI 10.1007/978-981-10-3147-2_23
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means of evaporation of water through the stomata positioned on the foliar surface; this process produces cooling. Temperature modifications of a leaf are generated by changes in vapotranspiration rate and can be used to measure evaporation rate (i.e., vapor mass lost per surface and time units) in single leaf or to evaluate crop vitality. This technique can also detect water content in specific areas of a leaf (necrosis, treatments with water repellent, etc.). In a leaf, changes of the water content (WC) caused by severe climatic conditions lead to alterations in transpiration rate through an active regulation mechanism of the stomatal opening. Thermography can visualize the effects of these changes in real time [12], thanks the low thermal capacity of a thin leaf (see Fig. 1). IRT application is based on the direct dependency between transpiration and leaves temperatures. Figure 2 illustrates clearly this relationship showing evaporation rate of bean leaves in the sam
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