Passive RFID, a new technology for dense and long-term monitoring of unstable structures: review and prospective.
Authors: Le Breton Mathieu , Baillet Laurent , Larose Éric , Rey Etienne , Jongmans Denis , Guyoton Fabrice , Benech Philippe 
Published: March 2020

&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Billions of passive radiofrequency tags are produced by the Radio-Frequency Identification (RFID) industry every year to identify goods remotely. New research and business applications are continuously arising, including recently localization and sensing for earth science. Indeed, the cost of tags is often several orders of magnitudes below conventional outdoor sensors used in earth science, allowing to deploy up to thousands of tags with minimal investment. Furthermore, passive wireless tags require little maintenance, which fits well for years-long monitoring. This study reviews the earth science applications that are being developed today, that use RFID devices available on the market, i.e., 900&amp;#160;MHz far-field tags and 125&amp;#160;kHz near-field tags.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Ground displacements of centimeters to hundreds of meters can be monitored using RFID location techniques. Indeed, RFID tags were firstly used in earth science to track the displacement of riverine and coastal sediments due to bedloading. Near-field tags inserted in pebbles can be identified typically up to 0.5&amp;#160;m from the reading device even when buried. The tags are read either by fixed portals or by a mobile device, obtaining either high space or time resolution data, respectively. Very recently, measuring the phase difference of arrival of far-field tags allowed to estimate displacements with centimetric accuracy, with a tag-reader distance up to 50&amp;#160;m. That allowed measuring the ground displacements continuously relatively to a fixed reader, or to estimate tags location placed on the ground by carrying a reader over a drone using the synthetic aperture radar method. Alternatively, RFID tags can also be used for sensing the evolution over time of the temperature, moisture level, vibrations, resonant frequency or crack opening of a geologic object.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; This review presents multiple applications for monitoring unstable rock/earth structures using RFID. First, slow landslides can be monitored with accurate displacement monitoring and with soil moisture sensors. Then, prone-to-failure rock columns could be monitored by sensing crack opening or resonant frequency, using the same tags as with the concrete structure applications. Finally, sediment loading due to rapid mass movements such as floods, debris flows, tsunami or typhoons, have been studied largely using tags placed into pebbles.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Author&amp;#8217;s published work on the topic:&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Le Breton, M., Baillet, L., Larose, E., Rey, E., Benech, P., Jongmans, D., Guyoton, F., 2017. Outdoor UHF RFID: Phase Stabilization for Real-World Applications. IEEE Journal of Radio Frequency Identification 1, 279&amp;#8211;290.&lt;/li&gt;
&lt;li&gt;Le Breton, M., Baillet, L., Larose, E., Rey, E., Benech, P., Jongmans, D., Guyoton, F., Jaboyedoff, M., 2019. Passive radio-frequency identification ranging, a dense and weather-robust technique for landslide displacement monitoring. Engineering Geology 250, 1&amp;#8211;10.&lt;/li&gt;
&lt;li&gt;Le Breton, M., 2019. Suivi temporel d&amp;#8217;un glissement de terrain &amp;#224; l&amp;#8217;aide d&amp;#8217;&amp;#233;tiquettes RFID passives, coupl&amp;#233; &amp;#224; l&amp;#8217;observation de pluviom&amp;#233;trie et de bruit sismique ambiant (PhD Thesis). Universit&amp;#233; Grenoble Alpes, ISTerre, Grenoble, France.&lt;/li&gt;
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