Plant monitoring and assessment is the activity to get responses of the environmental treatment from plant behavior’s view. Leaf motion is one of physical indicator that has been used to investigate the existence of plant motion, representing the internal movement triggered by the circadian clock even under the constant environment . Measurement of leaf motion as a rhythmic output requires three basic steps : 1) Taking and collecting images at a regular interval, 2) Extracting the numeric angle or leaf length on the horizontal or vertical axis of the collected images. 3) Estimating the period, phase, and amplitude from the time series numeric data. Several systems have been developed to support those three basic steps to study the circadian rhythm [3, 4, 5]. However, those integrated systems require expensive hardware module or commercial software. Also, the applications focus on individual leaf image of the standard plant model. Meanwhile, during vegetative growth in plant production, multi leaves images in mature plant foliage is a visual indicator that can be used for characterizing the effect of environmental signals and the circadian rhythm. We have developed an automatic leaf motion capturing system based on Raspberry pi with infra-red camera . The system could take day-night time-lapse photography automatically with a certain time interval. 2D Optical flow method, implementing Lukas-Kanade technique with Shi-Tomasi corner detector, was applied to quantify the leaf motion with translation distance and direction angle as motion parameter [7, 8].
Several challenges and opportunities regarding this study are:
- Correlation between leaf motion and environmental treatment (water stress or high evapotranspiration).
- Behavior or leaf motion to response the environmental changes
- How to use the plant motion information in the practical farming management in tropical agriculture cultivation?
- Two-dimensional optical flow (x, y) has a limitation on characterizing the height direction of the leaf (z), so an extension to 3D (x, y, z) or multidimensional (x, y, z, …) optical flow is necessary to obtain more precise leaf motion investigation.
Currently, we conducting three topics regarding the challenges mentioned above:
- Leaf motion behavior in response to environmental treatment (water stress, high evapotranspiration, or in constant condition in plant factory)
- Development of multi-camera leaf motion tracking system for precise monitoring and assessment for mature plant foliage
- Application of 3D optical flow for leaf motion quantification
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 Edwards, K.D., Lynn, J.R., Gyula, P., Nagy, F. and Millar, A.J., 2005. Natural allelic variation in the temperature-compensation mechanisms of the Arabidopsis thaliana circadian clock. Genetics, 170(1), pp.387- 400.
 Nugroho, A.P., Okayasu, T., Inoue, E., Hirai, Y., Mitsuoka, M., Sutiarso, L., 2015. Study on Plant Motion Measurement and Analysis Utilizing Computer Vision: Development of Automatic Plant Motion Analysis using Optical Flow, in: Joint Conference on Environmental Engineering in Agriculture 2015, Iwate, Japan, p. 12.
 Nugroho, A.P., Okayasu, T., Sakai, A., Inoue, E., Hirai, Y., Mitsuoka, M., Sutiarso, L., 2016b. Automatic leaf motion analysis using optical flow to diagnose plant behavior in response to environmental changes, in: Proceedings of the 8th International Symposium on Machinery and Mechatronics for Agriculture and Biosystems Engineering (ISMAB). Niigata, Japan, pp. 848–853.
 Nugroho, A.P., Okayasu, T., Taniguchi, R., Inoue, E., Hirai, Y., Mitsuoka, M., Sutiarso, L., 2016c. Quantification of 2D Lateral Leaf Motion on Mature Plants Foliage using Optical Flow to Study the Circadian Rhythms, in: Proceedings of the 2nd International Symposium on Agricultural and Biosystems Engineering (ISABE), Lombok, Indonesia.