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Optical sensing has been used to monitor the physiological responses of plants noninvasively and in real-time. In this study, we developed a low-cost plant sensor that performed a spectroscopic measurement at eight wavelengths in the visible region. The sensor head of the system was attached directly to the underside of the leaf, not blocking the light, and eliminating correction work because of the constant distance between the sensor head and the sample. The collected data was shared in the cloud via a network, thereby enabling remote monitoring. The characteristics of the plant sensor as a spectral photometer were validated, with major wavelengths also showing good correlations with those of a conventional spectrometer. The reflectance of 620 nm in this sensor detected plant aging indicator chlorophyll, and 550 nm detected stress indicator xanthophyll. In the field test, these plant physiological responses, seasonal leaf color changes and environmental stresses, were observed remotely. The results indicate that the novel spectroscopic measurement from the underside of the leaf is effective to realize accurate and stable measurement of the plant leaf. The plant sensor can be a powerful tool in the field of agriculture and ecological study by realizing simultaneous, multi-point and remote monitoring at a low cost. • A small sensor, securely attached to the underside of plants, was designed for spectroscopic measurements. • This method facilitates remote monitoring of plant physiological responses in real-time. • Long-term observations can detect color changes and environmental stress remotely.
Kohzuma et al. (Sat,) studied this question.