{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,14]],"date-time":"2026-02-14T11:25:14Z","timestamp":1771068314895,"version":"3.50.1"},"reference-count":79,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2023,3,29]],"date-time":"2023-03-29T00:00:00Z","timestamp":1680048000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000781","name":"European Research Council (ERC) under the ERC-2017-STG SENTIFLEX project","doi-asserted-by":"publisher","award":["755617"],"award-info":[{"award-number":["755617"]}],"id":[{"id":"10.13039\/501100000781","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Ram\u00f3n y Cajal Contract (Spanish Ministry of Science, Innovation and Universities)","award":["755617"],"award-info":[{"award-number":["755617"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Optical Earth Observation is often limited by weather conditions such as cloudiness. Radar sensors have the potential to overcome these limitations, however, due to the complex radar-surface interaction, the retrieving of crop biophysical variables using this technology remains an open challenge. Aiming to simultaneously benefit from the optical domain background and the all-weather imagery provided by radar systems, we propose a data fusion approach focused on the cross-correlation between radar and optical data streams. To do so, we analyzed several multiple-output Gaussian processes (MOGP) models and their ability to fuse efficiently Sentinel-1 (S1) Radar Vegetation Index (RVI) and Sentinel-2 (S2) vegetation water content (VWC) time series over a dry agri-environment in southern Argentina. MOGP models not only exploit the auto-correlations of S1 and S2 data streams independently but also the inter-channel cross-correlations. The S1 RVI and S2 VWC time series at the selected study sites being the inputs of the MOGP models proved to be closely correlated. Regarding the set of assessed models, the Convolutional Gaussian model (CONV) delivered noteworthy accurate data fusion results over winter wheat croplands belonging to the 2020 and 2021 campaigns (NRMSEwheat2020 = 16.1%; NRMSEwheat2021 = 10.1%). Posteriorly, we removed S2 observations from the S1 &amp; S2 dataset corresponding to the complete phenological cycles of winter wheat from September to the end of December to simulate the presence of clouds in the scenes and applied the CONV model at the pixel level to reconstruct spatiotemporally-latent VWC maps. After applying the fusion strategy, the phenology of winter wheat was successfully recovered in the absence of optical data. Strong correlations were obtained between S2 VWC and S1 &amp; S2 MOGP VWC reconstructed maps for the assessment dates (R2\u00afwheat\u22122020 = 0.95, R2\u00afwheat\u22122021 = 0.96). Altogether, the fusion of S1 SAR and S2 optical EO data streams with MOGP offers a powerful innovative approach for cropland trait monitoring over cloudy high-latitude regions.<\/jats:p>","DOI":"10.3390\/rs15071822","type":"journal-article","created":{"date-parts":[[2023,3,30]],"date-time":"2023-03-30T01:05:26Z","timestamp":1680138326000},"page":"1822","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":16,"title":["Synergy of Sentinel-1 and Sentinel-2 Time Series for Cloud-Free Vegetation Water Content Mapping with Multi-Output Gaussian Processes"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2268-2674","authenticated-orcid":false,"given":"Gabriel","family":"Caballero","sequence":"first","affiliation":[{"name":"Image Processing Laboratory (IPL), University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, Paterna, 46980 Valencia, Spain"}]},{"given":"Alejandro","family":"Pezzola","sequence":"additional","affiliation":[{"name":"Remote Sensing and SIG Laboratory, Hilario Ascasubi Agricultural Experimental Station, National Institute of Agricultural Technology (INTA), Hilario Ascasubi 8142, Buenos Aires, Argentina"}]},{"given":"Cristina","family":"Winschel","sequence":"additional","affiliation":[{"name":"Remote Sensing and SIG Laboratory, Hilario Ascasubi Agricultural Experimental Station, National Institute of Agricultural Technology (INTA), Hilario Ascasubi 8142, Buenos Aires, Argentina"}]},{"given":"Paolo","family":"Sanchez Angonova","sequence":"additional","affiliation":[{"name":"Remote Sensing and SIG Laboratory, Hilario Ascasubi Agricultural Experimental Station, National Institute of Agricultural Technology (INTA), Hilario Ascasubi 8142, Buenos Aires, Argentina"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6718-3679","authenticated-orcid":false,"given":"Alejandra","family":"Casella","sequence":"additional","affiliation":[{"name":"Permanent Observatory of Agro-Ecosystems, Climate and Water Institute-National Agricultural Research Centre (ICyA-CNIA), National Institute of Agricultural Technology (INTA), Nicol\u00e1s Repetto s\/n, Hurlingham 1686, Buenos Aires, Argentina"}]},{"given":"Luciano","family":"Orden","sequence":"additional","affiliation":[{"name":"Remote Sensing and SIG Laboratory, Hilario Ascasubi Agricultural Experimental Station, National Institute of Agricultural Technology (INTA), Hilario Ascasubi 8142, Buenos Aires, Argentina"},{"name":"Centro de Investigaci\u00f3n e Innovaci\u00f3n Agroalimentaria y Agroambiental (CIAGRO-UMH), GIAAMA Reseach Group, Universidad Miguel Hern\u00e1ndez, Carretera de Beniel Km, 03312 Orihuela, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5010-0179","authenticated-orcid":false,"given":"Mat\u00edas","family":"Salinero-Delgado","sequence":"additional","affiliation":[{"name":"Image Processing Laboratory (IPL), University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, Paterna, 46980 Valencia, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6957-0269","authenticated-orcid":false,"given":"Pablo","family":"Reyes-Mu\u00f1oz","sequence":"additional","affiliation":[{"name":"Image Processing Laboratory (IPL), University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, Paterna, 46980 Valencia, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0784-7717","authenticated-orcid":false,"given":"Katja","family":"Berger","sequence":"additional","affiliation":[{"name":"Image Processing Laboratory (IPL), University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, Paterna, 46980 Valencia, Spain"},{"name":"Mantle Labs GmbH, Gr\u00fcnentorgasse 19\/4, 1090 Vienna, Austria"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2819-6979","authenticated-orcid":false,"given":"Jes\u00fas","family":"Delegido","sequence":"additional","affiliation":[{"name":"Image Processing Laboratory (IPL), University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, Paterna, 46980 Valencia, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6313-2081","authenticated-orcid":false,"given":"Jochem","family":"Verrelst","sequence":"additional","affiliation":[{"name":"Image Processing Laboratory (IPL), University of Valencia, C\/Catedr\u00e1tico Jos\u00e9 Beltr\u00e1n 2, Paterna, 46980 Valencia, Spain"}]}],"member":"1968","published-online":{"date-parts":[[2023,3,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"273","DOI":"10.1016\/j.isprsjprs.2015.05.005","article-title":"Optical remote sensing and the retrieval of terrestrial vegetation bio-geophysical properties\u2014A review","volume":"108","author":"Verrelst","year":"2015","journal-title":"ISPRS J. 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