{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T14:57:34Z","timestamp":1777647454292,"version":"3.51.4"},"reference-count":47,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2019,10,11]],"date-time":"2019-10-11T00:00:00Z","timestamp":1570752000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001659","name":"Deutsche Forschungsgemeinschaft","doi-asserted-by":"publisher","award":["JO 1262\/2-1"],"award-info":[{"award-number":["JO 1262\/2-1"]}],"id":[{"id":"10.13039\/501100001659","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>A considerable amount of water is stored in vegetation, especially in regions with high precipitation rates. Knowledge of the vegetation water status is essential to monitor changes in ecosystem health and to assess the vegetation influence on the water budget. In this study, we develop and validate an approach to estimate the gravimetric vegetation water content (mg), defined as the amount of water [kg] per wet biomass [kg], based on the attenuation of microwave radiation through vegetation. mg is expected to be more closely related to the actual water status of a plant than the area-based vegetation water content (VWC), which expresses the amount of water [kg] per unit area [m2]. We conducted the study at the field scale over an entire growth cycle of a winter wheat field. Tower-based L-band microwave measurements together with in situ measurements of vegetation properties (i.e., vegetation height, and mg for validation) were performed. The results indicated a strong agreement between the in situ measured and retrieved mg (R2 of 0.89), with mean and standard deviation (STD) values of 0.55 and 0.26 for the in situ measured mg and 0.57 and 0.19 for the retrieved mg, respectively. Phenological changes in crop water content were captured, with the highest values of mg obtained during the growth phase of the vegetation (i.e., when the water content of the plants and the biomass were increasing) and the lowest values when the vegetation turned fully senescent (i.e., when the water content of the plant was the lowest). Comparing in situ measured mg and VWC, we found their highest agreement with an R2 of 0.95 after flowering (i.e., when the vegetation started to lose water) and their main differences with an R2 of 0.21 during the vegetative growth of the wheat vegetation (i.e., where the mg was constant and VWC increased due to structural changes in vegetation). In addition, we performed a sensitivity analysis on the vegetation volume fraction (\u03b4), an input parameter to the proposed approach which represents the volume percentage of solid plant material in air. This \u03b4-parameter is shown to have a distinct impact on the thermal emission at L-band, but keeping \u03b4 constant during the growth cycle of the winter wheat appeared to be valid for these mg retrievals.<\/jats:p>","DOI":"10.3390\/rs11202353","type":"journal-article","created":{"date-parts":[[2019,10,11]],"date-time":"2019-10-11T10:53:03Z","timestamp":1570791183000},"page":"2353","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":13,"title":["Estimating Gravimetric Water Content of a Winter Wheat Field from L-Band Vegetation Optical Depth"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6582-1278","authenticated-orcid":false,"given":"Thomas","family":"Meyer","sequence":"first","affiliation":[{"name":"Agrosphere (IBG-3), Institute of Bio- and Geosciences, Forschungszentrum J\u00fclich GmbH, 52428 J\u00fclich, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1760-2425","authenticated-orcid":false,"given":"Thomas","family":"Jagdhuber","sequence":"additional","affiliation":[{"name":"Microwaves and Radar Institute, German Aerospace Center, P.O. BOX 1116, 82234 Wessling, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1169-3098","authenticated-orcid":false,"given":"Mar\u00eda","family":"Piles","sequence":"additional","affiliation":[{"name":"Image Processing Lab, University of Valencia, Parc cient\u00edfic, 46980 Paterna, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Anita","family":"Fink","sequence":"additional","affiliation":[{"name":"Microwaves and Radar Institute, German Aerospace Center, P.O. BOX 1116, 82234 Wessling, Germany"},{"name":"Institute of applied Informatics, University of Augsburg, Alter Postweg 118, 86159 Augsburg, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jennifer","family":"Grant","sequence":"additional","affiliation":[{"name":"Netherlands Space Office, Centre Court, Prinses Beatrixlaan 2, 2595 AL The Hague, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8051-8517","authenticated-orcid":false,"given":"Harry","family":"Vereecken","sequence":"additional","affiliation":[{"name":"Agrosphere (IBG-3), Institute of Bio- and Geosciences, Forschungszentrum J\u00fclich GmbH, 52428 J\u00fclich, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8562-2073","authenticated-orcid":false,"given":"Fran\u00e7ois","family":"Jonard","sequence":"additional","affiliation":[{"name":"Agrosphere (IBG-3), Institute of Bio- and Geosciences, Forschungszentrum J\u00fclich GmbH, 52428 J\u00fclich, Germany"},{"name":"Earth and Life Institue, Universit\u00e9 catholique de Louvain, 1348 Louvain-la-Neuve, Belgium"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,10,11]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Meyer, T., Weiherm\u00fcller, L., Vereecken, H., and Jonard, F. (2018). Vegetation optical depth and soil moisture retrieved from L-band radiometry over the growth cycle of a winter wheat. Remote Sens., 10.","DOI":"10.3390\/rs10101637"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"757","DOI":"10.1109\/36.158870","article-title":"A dielectric model of the vegetation effects on the microwave emission from soils","volume":"30","author":"Schmugge","year":"1992","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"550","DOI":"10.1109\/TGRS.1987.289833","article-title":"Microwave dielectric spectrum of vegetation\u2014Part II: Dual-dispersion model","volume":"5","author":"Ulaby","year":"1987","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"350","DOI":"10.1016\/j.rse.2007.03.029","article-title":"Vegetation water content during SMEX04 from ground data and Landsat 5 thematic mapper imagery","volume":"112","author":"Yilmaz","year":"2008","journal-title":"Remote Sens. Environ."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Fink, A., Jagdhuber, T., Piles, M., Grant, J., Baur, M., Link, M., and Entekhabi, D. (2018, January 22\u201327). Estimating gravimetric moisture of vegetation using an attenuation-based multi-sensor approach. Proceedings of the IEEE International Geoscience and Remote Sensing Symposium, Valencia, Spain.","DOI":"10.1109\/IGARSS.2018.8518949"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"475","DOI":"10.1016\/j.rse.2003.10.021","article-title":"Vegetation water content mapping using Landsat data derived normalized difference water index for corn and soybeans","volume":"92","author":"Jackson","year":"2004","journal-title":"Remote Sens. Environ."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"225","DOI":"10.1016\/j.rse.2005.07.008","article-title":"Vegetation water content estimation for corn and soybeans using spectral indices derived from MODIS near- and short-wave infrared bands","volume":"98","author":"Chen","year":"2005","journal-title":"Remote Sens. Environ."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"447","DOI":"10.1016\/j.rse.2004.03.019","article-title":"Upscaling ground observations of vegetation water content, canopy height, and leaf area index during SMEX02 using aircraft and Landsat imagery","volume":"92","author":"Anderson","year":"2004","journal-title":"Remote Sens. Environ."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"42","DOI":"10.1016\/j.rse.2006.12.002","article-title":"Estimates of surface soil moisture under grass covers using L-band radiometry","volume":"109","author":"Saleh","year":"2007","journal-title":"Remote Sens. Environ."},{"key":"ref_10","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_11","doi-asserted-by":"crossref","first-page":"203","DOI":"10.1016\/0034-4257(91)90057-D","article-title":"Vegetation effects on the microwave emission of soils","volume":"36","author":"Jackson","year":"1991","journal-title":"Remote Sens. Environ."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"238","DOI":"10.1016\/j.rse.2017.01.024","article-title":"Modelling the passive microwave signature from land surfaces: A review of recent results and application to the L-band SMOS & SMAP soil moisture retrieval algorithms","volume":"192","author":"Wigneron","year":"2017","journal-title":"Remote Sens. Environ."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"716","DOI":"10.1109\/36.225537","article-title":"Microwave emission of vegetation: Sensitivity to leaf characteristics","volume":"31","author":"Wigneron","year":"1993","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"406","DOI":"10.1109\/TGRS.1984.350644","article-title":"Microwave dielectric properties of plant materials","volume":"4","author":"Ulaby","year":"1984","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_15","unstructured":"O\u2019Neill, P., Chan, S., Njoku, E., Jackson, T., and Bindlish, R. (2015). Algorithm theoretical basis document (ATBD): Level 2 & 3 soil moisture (passive) data products. Soil Moisture Active Passive (SMAP), Jet Propulsion Laboratory."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"666","DOI":"10.1109\/JPROC.2010.2043032","article-title":"The SMOS mission: New tool for monitoring key elements ofthe global water cycle","volume":"98","author":"Kerr","year":"2010","journal-title":"Proc. IEEE"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"704","DOI":"10.1109\/JPROC.2010.2043918","article-title":"The soil moisture active passive (SMAP) mission","volume":"98","author":"Entekhabi","year":"2010","journal-title":"Proc. IEEE"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Grant, J., Wigneron, J., Williams, M., Scholze, M., and Kerr, Y. (2014, January 13\u201318). Working towards a global-scale vegetation water product from SMOS optical depth. Proceedings of the IEEE International Geoscience and Remote Sensing Symposium, Quebec City, QC, Canada.","DOI":"10.1109\/IGARSS.2014.6946413"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Ulaby, F.T., Long, D.G., Blackwell, W.J., Elachi, C., Fung, A.K., Ruf, C., Sarabandi, K., Zebker, H.A., and Van Zyl, J. (2014). Microwave Radar and Radiometric Remote Sensing, University of Michigan Press.","DOI":"10.3998\/0472119356"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Grant, J.P., Wigneron, J., Drusch, M., Williams, M., Law, B.E., Novello, N., and Kerr, Y. (2012, January 22\u201327). Investigating temporal variations in vegetation water content derived from SMOS optical depth. Proceedings of the IEEE International Geoscience and Remote Sensing Symposium, Munich, Germany.","DOI":"10.1109\/IGARSS.2012.6350590"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"3095","DOI":"10.1109\/TGRS.2014.2368831","article-title":"Estimation of hydraulic properties of a sandy soil using ground-based active and passive microwave remote sensing","volume":"53","author":"Jonard","year":"2015","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"257","DOI":"10.1016\/S0031-8914(46)80066-1","article-title":"The effective permeability of mixtures of solids","volume":"12","author":"Polder","year":"1946","journal-title":"Physica"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"101","DOI":"10.1016\/0022-1694(95)02970-2","article-title":"Passive microwave remote sensing of soil moisture","volume":"184","author":"Njoku","year":"1996","journal-title":"J. Hydrol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2224","DOI":"10.1109\/TGRS.2009.2037749","article-title":"WindSat global soil moisture retrieval and validation","volume":"48","author":"Li","year":"2010","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2376","DOI":"10.1016\/j.rse.2011.04.037","article-title":"Comparison of vegetation water contents derived from shortwave-infrared and passive-microwave sensors over central Iowa","volume":"115","author":"Hunt","year":"2011","journal-title":"Remote Sens. Environ."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"746","DOI":"10.1109\/TGRS.1985.289393","article-title":"Microwave attenuation properties of vegetation canopies","volume":"5","author":"Ulaby","year":"1985","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"520","DOI":"10.1109\/TGRS.1984.6499163","article-title":"Measured microwave emission and scattering in vegetation canopies","volume":"6","author":"Brunfeldt","year":"1984","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/j.rse.2015.10.021","article-title":"Comparison of SMOS and AMSR-E vegetation optical depth to four MODIS-based vegetation indices","volume":"172","author":"Grant","year":"2016","journal-title":"Remote Sens. Environ."},{"key":"ref_29","first-page":"37","article-title":"Microwave radiation of the earth\u2019s surface in the presence of vegetation cover","volume":"24","author":"Kirdyashev","year":"1979","journal-title":"Radio Eng. Electron. Phys."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1381","DOI":"10.1175\/BAMS-87-10-1381","article-title":"GSWP-2: Multimodel analysis and implications for our perception of the land surface","volume":"87","author":"Dirmeyer","year":"2006","journal-title":"Bull. Am. Meteorol. Soc."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"4285","DOI":"10.1016\/j.rse.2008.07.015","article-title":"Microwave vegetation indices for short vegetation covers from satellite passive microwave sensor AMSR-E","volume":"112","author":"Shi","year":"2008","journal-title":"Remote Sens. Environ."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"639","DOI":"10.1016\/j.rse.2006.10.014","article-title":"L-band Microwave Emission of the Biosphere (L-MEB) model: Description and calibration against experimental data sets over crop fields","volume":"107","author":"Wigneron","year":"2007","journal-title":"Remote Sens. Environ."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"947","DOI":"10.1109\/36.298024","article-title":"Microwave (1\u2013100 GHz) dielectric model of leaves","volume":"32","author":"Matzler","year":"1994","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"331","DOI":"10.1023\/A:1008382309369","article-title":"Global optimization by multilevel coordinate search","volume":"14","author":"Huyer","year":"1999","journal-title":"J. Glob. Optim."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"308","DOI":"10.1093\/comjnl\/7.4.308","article-title":"A simplex method for function minimization","volume":"7","author":"Nelder","year":"1965","journal-title":"Comput. J."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"310","DOI":"10.1007\/BF02922010","article-title":"Dielectric properties of heterogeneous mixtures with a polar constituent","volume":"11","year":"1964","journal-title":"Appl. Sci. Res. Sect. B"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"61","DOI":"10.1016\/0034-4257(93)90032-S","article-title":"Inversion of surface parameters from passive microwave measurements over a soybean field","volume":"46","author":"Wigneron","year":"1993","journal-title":"Remote Sens. Environ."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"384","DOI":"10.1109\/36.54364","article-title":"A semiempirical model for interpreting microwave emission from semiarid land surfaces as seen from space","volume":"28","author":"Kerr","year":"1990","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_39","unstructured":"Wegm\u00fcller, U., M\u00e4tzler, C., and Njoku, E.G. (1995). Canopy opacity models. Passive Microwave Remote Sensing of Land-Atmosphere Interactions, VSP."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1016\/0034-4257(90)90086-2","article-title":"Seasonal evolution of microwave radiation from an oat field","volume":"31","author":"Matzler","year":"1990","journal-title":"Remote Sens. Environ."},{"key":"ref_41","unstructured":"Tsang, L., and Choe, Y. (1983). A Mathematical Characterization of Vegetation Effect on Microwave Remote Sensing from the Earth, Texas A\/M University, Remote Sensing Center."},{"key":"ref_42","unstructured":"Grant, J.P. (2016). Global-scale Dynamic Monitoring of Vegetation Water Status for Improving Carbon Flux Estimates (VEGWAC), Lund University. ESA STSE Final Report."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"162","DOI":"10.1016\/j.fcr.2012.12.011","article-title":"Allometric analysis of the effects of density on reproductive allocation and harvest index in 6 varieties of wheat (Triticum)","volume":"144","author":"Qin","year":"2013","journal-title":"Field Crop. Res."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1109\/LGRS.2005.843983","article-title":"Analytical derivation of the vegetation optical depth from the microwave polarization difference index","volume":"2","author":"Meesters","year":"2005","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.rse.2011.10.024","article-title":"Effective tree scattering and opacity at L-band","volume":"118","author":"Kurum","year":"2012","journal-title":"Remote Sens. Environ."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"1081","DOI":"10.1109\/LGRS.2014.2381641","article-title":"How many parameters can be maximally estimated from a set of measurements?","volume":"12","author":"Konings","year":"2015","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"178","DOI":"10.1016\/j.rse.2015.11.009","article-title":"Vegetation optical depth and scattering albedo retrieval using time series of dual-polarized L-band radiometer observations","volume":"172","author":"Konings","year":"2016","journal-title":"Remote Sens. Environ."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/11\/20\/2353\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T13:25:05Z","timestamp":1760189105000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/11\/20\/2353"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,10,11]]},"references-count":47,"journal-issue":{"issue":"20","published-online":{"date-parts":[[2019,10]]}},"alternative-id":["rs11202353"],"URL":"https:\/\/doi.org\/10.3390\/rs11202353","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,10,11]]}}}