{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,3]],"date-time":"2026-03-03T23:19:22Z","timestamp":1772579962144,"version":"3.50.1"},"reference-count":28,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2021,2,2]],"date-time":"2021-02-02T00:00:00Z","timestamp":1612224000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Agronomy"],"abstract":"<jats:p>Sap flow measurements of trees are today the most common method to determine evapotranspiration at the tree and the forest\/crop canopy level. They provide independent measurements for flux comparisons and model validation. The most common approach to measure the sap flow is based on intrusive solutions with heaters and thermal sensors. This sap flow sensor technology is not very reliable for more than one season crop; it is intrusive and not adequate for low diameter trunk trees. The non-invasive methods comprise mostly Radio-frequency (RF) technologies, typically using satellite or air-born sources. This system can monitor large fields but cannot measure sap levels of a single plant (precision agriculture). This article studies the hypothesis to use of RF signals attenuation principle to detect variations in the quantity of water present in a single plant. This article presents a well-defined experience to measure water content in leaves, by means of high gains RF antennas, spectrometer, and a robotic arm. Moreover, a similar concept is studied with an off-the-shelf radar solution\u2014for the automotive industry\u2014to detect changes in the water presence in a single plant and leaf. The conclusions indicate a novel potential application of this technology to precision agriculture as the experiments data is directly related to the sap flow variations in plant.<\/jats:p>","DOI":"10.3390\/agronomy11020279","type":"journal-article","created":{"date-parts":[[2021,2,2]],"date-time":"2021-02-02T13:01:12Z","timestamp":1612270872000},"page":"279","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Potential Non-Invasive Technique for Accessing Plant Water Contents Using a Radar System"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0255-5005","authenticated-orcid":false,"given":"Lu\u00eds Carlos","family":"Santos","sequence":"first","affiliation":[{"name":"INESC Technology and Science (INESC TEC), 4200-465 Porto, Portugal"},{"name":"Department of Engineering, University of Tr\u00e1s-os-Montes e Alto Douro (UTAD), 5000-801 Vila Real, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8486-6113","authenticated-orcid":false,"given":"Filipe Neves","family":"dos Santos","sequence":"additional","affiliation":[{"name":"INESC Technology and Science (INESC TEC), 4200-465 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2440-9153","authenticated-orcid":false,"given":"Raul","family":"Morais","sequence":"additional","affiliation":[{"name":"INESC Technology and Science (INESC TEC), 4200-465 Porto, Portugal"},{"name":"Department of Engineering, University of Tr\u00e1s-os-Montes e Alto Douro (UTAD), 5000-801 Vila Real, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7449-8193","authenticated-orcid":false,"given":"C\u00e2ndido","family":"Duarte","sequence":"additional","affiliation":[{"name":"INESC Technology and Science (INESC TEC), 4200-465 Porto, Portugal"},{"name":"Faculty of Engineering, University of Porto (FEUP), 4200-465 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2021,2,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"467","DOI":"10.1098\/rstb.2007.2164","article-title":"Shrink and share: Humanity\u2019s present and future Ecological Footprint","volume":"363","author":"Kitzes","year":"2007","journal-title":"Philos. 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