{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T15:58:06Z","timestamp":1785772686928,"version":"3.56.0"},"reference-count":13,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2020,7,22]],"date-time":"2020-07-22T00:00:00Z","timestamp":1595376000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100014440","name":"Ministerio de Ciencia, Innovaci\u00f3n y Universidades","doi-asserted-by":"publisher","award":["RTI2018-099008-B-C21"],"award-info":[{"award-number":["RTI2018-099008-B-C21"]}],"id":[{"id":"10.13039\/100014440","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100010198","name":"Ministerio de Econom\u00eda, Industria y Competitividad, Gobierno de Espa\u00f1a","doi-asserted-by":"publisher","award":["MDM-2016-600"],"award-info":[{"award-number":["MDM-2016-600"]}],"id":[{"id":"10.13039\/501100010198","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>At L-band (1\u20132 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the \u03c4-\u03c9 model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscript presents an analysis of the vegetation impact on GPS L1 C\/A (coarse acquisition code) signals in terms of attenuation and depolarization. A dual polarized instrument with commercial off-the-shelf (COTS) GPS receivers as back-ends was installed for more than a year under a beech forest collecting carrier-to-noise (C\/N0) data. These data were compared to different ground-truth datasets (greenness, blueness, and redness indices, sky cover index, rain data, leaf area index or LAI, and normalized difference vegetation index (NDVI)). The highest correlation observed is between C\/N0 and NDVI data, obtaining R2 coefficients larger than 0.85 independently from the elevation angle, suggesting that for beech forest, NDVI is a good descriptor of signal attenuation at L-band, which is known to be related to the vegetation optical depth (VOD). Depolarization effects were also studied, and were found to be significant at elevation angles as large as ~50\u00b0. Data were also fit to a simple \u03c4-\u03c9 model to estimate a single scattering albedo parameter (\u03c9) to try to compensate for vegetation scattering effects in soil moisture retrieval algorithms using GNSS-R. It is found that, even including dependence on the elevation angle (\u03c9(\u03b8e)), at elevation angles smaller than ~67\u00b0, the \u03c9(\u03b8e) model is not related to the NDVI. This limits the range of elevation angles that can be used for soil moisture retrievals using GNSS-R. Finally, errors of the GPS-derived position were computed over time to assess vegetation impact on the accuracy of the positioning.<\/jats:p>","DOI":"10.3390\/rs12152352","type":"journal-article","created":{"date-parts":[[2020,7,23]],"date-time":"2020-07-23T11:26:01Z","timestamp":1595503561000},"page":"2352","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9514-4992","authenticated-orcid":false,"given":"Adriano","family":"Camps","sequence":"first","affiliation":[{"name":"CommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c\/Jordi Girona 1-3, 08034 Barcelona, Spain"},{"name":"Institut d\u2019Estudis Espacials de Catalunya-IEEC\/CTE-UPC, Gran Capit\u00e0, 2-4, Edifici Nexus, despatx 201, 08034 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alberto","family":"Alonso-Arroyo","sequence":"additional","affiliation":[{"name":"CommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c\/Jordi Girona 1-3, 08034 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0031-0802","authenticated-orcid":false,"given":"Hyuk","family":"Park","sequence":"additional","affiliation":[{"name":"CommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c\/Jordi Girona 1-3, 08034 Barcelona, Spain"},{"name":"Institut d\u2019Estudis Espacials de Catalunya-IEEC\/CTE-UPC, Gran Capit\u00e0, 2-4, Edifici Nexus, despatx 201, 08034 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6636-1587","authenticated-orcid":false,"given":"Raul","family":"Onrubia","sequence":"additional","affiliation":[{"name":"CommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c\/Jordi Girona 1-3, 08034 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8517-2415","authenticated-orcid":false,"given":"Daniel","family":"Pascual","sequence":"additional","affiliation":[{"name":"CommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c\/Jordi Girona 1-3, 08034 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8500-5534","authenticated-orcid":false,"given":"Jorge","family":"Querol","sequence":"additional","affiliation":[{"name":"Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, 29 Avenue John F. Kennedy, Luxembourg L-1855, Luxembourg"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,7,22]]},"reference":[{"key":"ref_1","first-page":"215","article-title":"The Effect of Broadleaf Canopies on Survey-grade Horizontal GPS\/GLONASS Measurements","volume":"62","author":"Meyer","year":"2002","journal-title":"Surv. L. Inf. Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"331","DOI":"10.1016\/0034-4257(94)00081-W","article-title":"A simple algorithm to retrieve soil moisture and vegetation biomass using passive microwave measurements over crop fields","volume":"51","author":"Wigneron","year":"1995","journal-title":"Remote Sens. Environ."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"416","DOI":"10.1109\/TGRS.2003.817976","article-title":"Characterizing the Dependence of Vegetation Model Parameters on Crop Structure, Incidence Angle, and Polarization at L-Band","volume":"42","author":"Wigneron","year":"2004","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"282","DOI":"10.1109\/LGRS.2011.2166242","article-title":"Vegetation Water Content Estimation Using GNSS Measurements","volume":"9","author":"Camps","year":"2012","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_5","unstructured":"AntennaLab (2020, July 22). Anechoic Chamber. Available online: http:\/\/www.tsc.upc.edu\/antennalab\/."},{"key":"ref_6","unstructured":"NASA (2020, July 22). LAI and NDVI Maps, Available online: http:\/\/neo.sci.gsfc.nasa.gov\/."},{"key":"ref_7","unstructured":"(2020, July 22). MeteOlot. 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Remote Sens., 10.","DOI":"10.3390\/rs10081245"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Camps, A., Vall\u00b7llossera, M., Park, H., Portal, G., and Rossato, L. (2018). Sensitivity of TDS-1 GNSS-Reflectivity to Soil Moisture: Global and Regional Differences and Impact of Different Spatial Scales. Remote Sens., 10.","DOI":"10.3390\/rs10111856"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"e0191017","DOI":"10.1371\/journal.pone.0191017","article-title":"Real-time positioning in logging: Effects of forest stand characteristics, topography, and line-of-sight obstructions on GNSS-RF transponder accuracy and radio signal propagation","volume":"13","author":"Zimbelman","year":"2018","journal-title":"PLoS ONE"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Camps, A., Park, H., Castellv\u00ed, J., Corbera, J., and Ascaso, E. (2020). Single-Pass Soil Moisture Retrievals Using GNSS-R: Lessons Learned. Remote Sens., 12.","DOI":"10.3390\/rs12122064"}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/12\/15\/2352\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:50:45Z","timestamp":1760176245000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/12\/15\/2352"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,7,22]]},"references-count":13,"journal-issue":{"issue":"15","published-online":{"date-parts":[[2020,8]]}},"alternative-id":["rs12152352"],"URL":"https:\/\/doi.org\/10.3390\/rs12152352","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,7,22]]}}}