Assessing plant water status is important for monitoring plant physiology. Previous studies showed that radio waves are attenuated when passing through vegetation such as trees. The degree of radio frequency (RF) loss has previously been measured for various tree types but the relationship between water content and RF loss has not been quantified. In this study, the amount of water inside leaves was expressed as an effective water path (EWP), the thickness of a hypothetical sheet of 100% water with the same mass. A 2.4331 GHz radio wave was transmitted through a wooden frame covered on both sides with 5 mm clear acrylic sheets and filled with Eucalyptus laevopinea leaves. The RF loss through the leaves was measured for different stages of drying. The results showed that there is a nonlinear relationship between effective water path (EWP) in mm and RF loss in dB. It can be concluded that 2.4 GHz frequency radio waves can be used to predict the water content inside eucalyptus leaves (0 < EWP < 14 mm; RMSE ± 0.87 mm) and demonstrates the potential to measure the water content of whole trees.
Allen, C.D., et al. (2010) A Global Overview of Drought and Heat-Induced Tree Mortality Reveals Emerging Climate Change Risks for Forests. Forest Ecology and Management, 259, 660-684. https://doi.org/10.1016/j.foreco.2009.09.001
Boland, D.J., et al. (2006) Forest Trees of Australia. 5th Edition, Victoria CSIRO Publishing, Victoria.
Matusick, G., Ruthrof, K., Brouwers, N., Dell, B. and Hardy, G. (2013) Sudden Forest Canopy Collapse Corresponding with Extreme Drought and Heat in a Mediterranean-Type Eucalypt Forest in Southwestern Australia. European Journal of Forest Research, 132, 497-510. https://doi.org/10.1007/s10342-013-0690-5
ABARES (2018) Australia’s State of the Forests Report. Department of Agriculture and Water Resources, Australian.
Belyazid, S. and Giuliana, Z. (2019) Water Limitation Can Negate the Effect of Higher Temperatures on Forest Carbon Sequestration. European Journal of Forest Research, 138, 287-297. https://doi.org/10.1007/s10342-019-01168-4
Kirkham, M.B. (2016) Elevated Carbon Dioxide: Impacts on Soil and Plant Water Relations. CRC Press, Boca Raton.
Osakabe, Y., Osakabe, K., Shinozaki, K. and Tran, L.S. (2014) Response of Plants to Water Stress. Frontiers in Plant Science, 5, 86. https://doi.org/10.3389/fpls.2014.00086
Pereira, J. and Pallardy, S. (1989) Water Stress Limitations to Tree Productivity. In: Biomass Production by Fast-Growing Trees, Springer, Berlin, 37-56. https://doi.org/10.1007/978-94-009-2348-5_3
Pallardy, S., Pereira, J. and Parker, W. (1991) Measuring the State of Water in Tree Systems. In: Lassoie, J.P. and Hinckley, T.M., Eds., Techniques and Approaches in Forest Tree Ecophysiology, CRC Press, Boca Raton, 28-76.
Zhou, J., Zhou, J., Ye, H., Ali, M.L., Nguyen, H.T. and Chen, P. (2020) Classification of Soybean Leaf Wilting Due to Drought Stress Using UAV-Based Imagery. Computers and Electronics in Agriculture, 175, Article ID: 105576.
Resh, H.M. (2015) Signs of Plant Nutritional and Physiological Disorders and Their Remedies. In: Hydroponics for the Home Grower, CRC Press, Boca Raton, 76-89. https://doi.org/10.1201/b18069-16
Peñuelas, J., Filella, I., Biel, C., Serrano, L. and Save, R. (1993) The Reflectance at the 950-970 nm Region as an Indicator of Plant Water Status. International Journal of Remote Sensing, 14, 1887-1905. https://doi.org/10.1080/01431169308954010
Peñ uelas, J., Filella, I., Serrano, L. and Save, R. (1996) Cell Wall Elasticity and Water Index (R970 nm/R900 nm) in Wheat under Different Nitrogen Availabilities. International Journal of Remote Sensing, 17, 373-382. https://doi.org/10.1080/01431169608949012
Datt, B. (1999) Remote Sensing of Water Content in Eucalyptus Leaves. Australian Journal of Botany, 47, 909-923. https://doi.org/10.1071/BT98042
Balachander, D., Rao, T.R. and Mahesh, G. (2013) RF Propagation Experiments in Agricultural Fields and Gardens for Wireless Sensor Communications. Progress in Electromagnetics Research C, 39, 103-118. https://doi.org/10.2528/PIERC13030710
Weissberger, M.A. (1982) An Initial Critical Summary of Models for Predicting the Attenuation of Radio Waves by Trees.
Seville, A. and Craig, K. (1995) Semi-Empirical Model for Millimetre-Wave Vegetation Attenuation Rates. Electronics Letters, 31, 1507-1508. https://doi.org/10.1049/el:19951000
Al-Nuaimi, M.O. and Stephens, R.B.L. (1998) Measurements and Prediction Model Optimisation for Signal Attenuation in Vegetation Media at Centimetre Wave Frequencies. IEE Proceedings-Microwaves, Antennas and Propagation, 145, 201-206. https://doi.org/10.1049/ip-map:19981883
Adegoke, A.S. (2014) Measurement of Propagation Loss in Trees at SHF Frequencies. Ph.D. Thesis, Department of Engineering, University of Leicester, Leicester.
Rogers, N.C., Seville, A., Richter, J., Ndzi, D., Savage, N., Caldeirinha, R., Shukla, A., Al-Nuaimi, M., Craig, K. and Vilar, E. (2002) A Generic Model of 1-60 GHz Radio Propagation through Vegetation. Final Report, Radio Agency, London.
Rappaport, T.S. (1996) Wireless Communications: Principles and Practice. Prentice Hall, Hoboken.
Hristos, T.A., Stavros, V., Theodoros, F., Christian, R., Loukas, P., Manuela, Z. and Jana, K. (2014) A Computational Model for Path Loss in Wireless Sensor Networks in Orchard Environments. Sensors, 14, 5118-5135. https://doi.org/10.3390/s140305118
LaGrone, A.H. (1960) Forecasting Television Service Fields. Proceedings of the IRE, 48, 1009-1015. https://doi.org/10.1109/JRPROC.1960.287501
Seville, A., Charriere, P.G.V., Powell, N. and Craig, K.H. (1995) Building Scatter and Vegetation Attenuation Measurements at 38 GHz. 9th International Conference on Antennas and Propagation (ICAP), Eindhoven, April 1995, 46-50. https://doi.org/10.1049/cp:19950380
Adegoke, A.S. and Siddle, D. (2015) Geometry Dependence of Vegetation Attenuation on Isolated Single Trees. European Journal of Engineering and Technology, 3, 36-42.
Azevedo, J.A.R. and Santos, F.E.S. (2011) An Empirical Propagation Model for Forest Environments at Tree Trunk Level (Technical Report). IEEE Transactions on Antennas and Propagation, 59, 2357. https://doi.org/10.1109/TAP.2011.2143664
Azevedo, J.A.R. and Santos, F.E.S. (2017) A Model to Estimate the Path Loss in Areas with Foliage of Trees. AEUE—International Journal of Electronics and Communications, 71, 157. https://doi.org/10.1016/j.aeue.2016.10.018
Andrade-Sanchez, P., Pierce, F.J. and Elliott, T.V. (2007) Performance Assessment of Wireless Sensor Networks in Agricultural Settings. ASABE Paper, 073076. https://doi.org/10.13031/2013.23185
Guo, X.-M. and Zhao, C. (2014) Propagation Model for 2.4 GHz Wireless Sensor Network in Four-Year-Old Young Apple Orchard. International Journal of Agricultural and Biological Engineering, 7, 47-53.
Al-Nuaimi, M.O. and Hammoudeh, A.M. (1993) Attenuation Functions of Microwave Signals Propagated through Trees. Electronics Letters, 29, 1307-1308. https://doi.org/10.1049/el:19930872
Adamy, D. (2015) Radio Propagation: Losses from Trees and Urban Areas. Journal of Electronic Defense, 38, 43.
Benzair, B. (1993) Characterisation of Radio Wave Propagation inside Building and through Vegetation. University of Bradford, Bradford.
Caldeirinha, R.F.S. (2001) Radio Characterisation of Single Trees at Micro and Millimetre Wave Frequencies. University of Glamorgan, Wales.
Yang, X., Guo, X., Li, M., Sun, C., Hao, L., Qu, L. and Wang, Y. (2013) An Empirical Model for 2.4 GHz Radio propagation in a Gala Apple Orchard and Evaluation of the Model Performance by Simulation. Transactions of the ASABE, 56, 1599-1611.
Perras, S. and Bouchard, L. (2002) Fading Characteristics of RF Signals Due to Foliage in Frequency Bands from 2 to 60 GHz. Proceedings of the 5th International Symposium on Wireless Personal Multimedia Communications, 1, 267-271. https://doi.org/10.1109/WPMC.2002.1088174
Muhammad, N.A., Rahman, T.A., Rahim, S.K.A., Kesavan, U. and Assis, M.S. (2013) Investigation of Wind and Rain Effects in a Foliated Tropical Region for Fixed Wireless Access. International Journal of Electronics, 101, 1314-1324. https://doi.org/10.1080/00207217.2013.853259
Le Vine, D.M. and Karam, M.A. (1996) Dependence of Attenuation in a Vegetation Canopy on Frequency and Plant Water Content. IEEE Transactions on Geoscience and Remote Sensing, 34, 1090-1096. https://doi.org/10.1109/36.536525
Nakajima, I., Ohyama, F., Juzoji, H. and Ta, M. (2019) Developing a Scanner for Assessing Foliage Moisture. Journal of Multimedia Information System, 6, 155-164. https://doi.org/10.33851/JMIS.2019.6.3.155
Schubert, F.M., Fleury, B.H. and Prieto-Cerdeira, R. (2009) Propagation Model for Wave Scattering Effects Caused by Trees. Proceedings COST Action IC0802 2nd Management Committee Meeting, Toulouse, France, 4-6 November.
Caldeirinha, R.F.S., Morgadinho, S., Frazão, L., Cuiñ as, I., Sanchéz, M. and AlNuaimi, M. (2006) Wind Incidence Effects on Channel Dynamics in Vegetation Media at 40 GHz. IEEE International Symposium on Geoscience and Remote Sensing, Denver, 31 July-4 August 2006, 1032-1035. https://doi.org/10.1109/IGARSS.2006.266
Salameh, H.A.S.M. (2019) Predicting Leaf State Effects on Radiowaves Based on Propagation Loss Measurements. MATEC Web of Conferences, 292, Article No. 02005. https://doi.org/10.1051/matecconf/201929202005
Peden, S., Bradbury, R.C., Lamb, D.W. and Hedley, M. (2021) A Model for RF Loss through Vegetation with Varying Water Content. Journal of Electromagnetic Analysis and Applications, 13, 41-56.