{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,15]],"date-time":"2026-01-15T04:52:39Z","timestamp":1768452759372,"version":"3.49.0"},"reference-count":42,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2014,7,29]],"date-time":"2014-07-29T00:00:00Z","timestamp":1406592000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The estimation of evapotranspiration of blue water (ETb) from farmlands, due to irrigation, is crucial to improve water management, especially in regions where water resources are scarce. Large scale ETb was previously obtained, based on the differences between remote sensing derived actual ET and values simulated from the Global Land Data Assimilation System (GLDAS). In this paper, we improve on the previous approach by enhancing the classification scheme employed so that it represents regions with common hydrometeorological conditions. Bias between the two data sets for reference areas (non-irrigated croplands) were identified per class, and used to adjust the remote sensing products. Different classifiers were compared and evaluated based on the generated bias curves per class and their variability. The results in Europe show that the k-means  classifier was better suited to identify the bias curves per class, capturing the dynamic range of these curves and minimizing their variability within each corresponding class. The method was applied in Africa and the classification and bias results were consistent with the findings in Europe. The ETb results were compared with existing literature and provided differences up to 50 mm\/year in Europe, while the comparison in Africa was found to be highly influenced by the assigned cover type and the heterogeneity of the pixel. Although further research is needed to fully understand the ETb values found, this paper shows a more robust approach to classify and characterize the bias between the two sets of ET data.<\/jats:p>","DOI":"10.3390\/rs6087026","type":"journal-article","created":{"date-parts":[[2014,7,29]],"date-time":"2014-07-29T10:58:58Z","timestamp":1406631538000},"page":"7026-7049","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Towards the Improvement of Blue Water Evapotranspiration Estimates by Combining Remote Sensing and Model Simulation"],"prefix":"10.3390","volume":"6","author":[{"given":"Mireia","family":"Romaguera","sequence":"first","affiliation":[{"name":"Faculty of Geo-Information Science and Earth Observation, University of Twente, 7500 AE Enschede, The Netherlands"},{"name":"Twente Water Centre, University of Twente, 7500 AE Enschede, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6670-6853","authenticated-orcid":false,"given":"Mhd.","family":"Salama","sequence":"additional","affiliation":[{"name":"Faculty of Geo-Information Science and Earth Observation, University of Twente, 7500 AE Enschede, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Maarten","family":"Krol","sequence":"additional","affiliation":[{"name":"Twente Water Centre, University of Twente, 7500 AE Enschede, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4769-5239","authenticated-orcid":false,"given":"Arjen","family":"Hoekstra","sequence":"additional","affiliation":[{"name":"Twente Water Centre, University of Twente, 7500 AE Enschede, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Zhongbo","family":"Su","sequence":"additional","affiliation":[{"name":"Faculty of Geo-Information Science and Earth Observation, University of Twente, 7500 AE Enschede, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2014,7,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"232","DOI":"10.1016\/j.jhydrol.2009.09.028","article-title":"An estimation of global virtual water flow and sources of water withdrawal for major crops and livestock products using a global hydrological model","volume":"384","author":"Hanasaki","year":"2010","journal-title":"J. Hydrol"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"187","DOI":"10.1016\/j.jhydrol.2009.11.024","article-title":"Spatially explicit assessment of global consumptive water uses in cropland: Green and blue water","volume":"384","author":"Liu","year":"2010","journal-title":"J. Hydrol"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1577","DOI":"10.5194\/hess-15-1577-2011","article-title":"The green, blue and grey water footprint of crops and derived crop products","volume":"15","author":"Mekonnen","year":"2011","journal-title":"Hydrol. Earth Syst. Sci"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"198","DOI":"10.1016\/j.jhydrol.2009.07.031","article-title":"Quantifying blue and green virtual water contents in global crop production as well as potential production losses without irrigation","volume":"384","author":"Siebert","year":"2010","journal-title":"J. Hydrol"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"535","DOI":"10.5194\/hess-9-535-2005","article-title":"Development and validation of the Global Map of Irrigation Areas","volume":"9","author":"Siebert","year":"2005","journal-title":"Hydrol. Earth Syst. Sci"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"3679","DOI":"10.1080\/01431160802698919","article-title":"Global Irrigated Area Map (GIAM), derived from remote sensing, for the end of the last millennium","volume":"30","author":"Thenkabail","year":"2009","journal-title":"Int. J. Remote Sens"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1177","DOI":"10.3390\/rs2041177","article-title":"Potential of using remote sensing techniques for global assessment of water footprint of crops","volume":"2","author":"Romaguera","year":"2010","journal-title":"Remote Sens"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"861","DOI":"10.14358\/PERS.78.8.861","article-title":"Determining irrigated areas and quantifying blue water use in Europe using remote sensing Meteosat Second Generation (MSG) products and Global Land Data Assimilation System (GLDAS) data","volume":"78","author":"Romaguera","year":"2012","journal-title":"Photogramm. Eng. Remote Sens"},{"key":"ref_9","first-page":"288","article-title":"Remote sensing method for estimating green and blue water footprint","volume":"352","author":"Neale","year":"2012","journal-title":"Remote Sensing and Hydrology"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"192","DOI":"10.1023\/A:1006355315251","article-title":"Irrigation performance indicators based on remotely sensed data: A review of literature","volume":"13","author":"Bastiaanssen","year":"1999","journal-title":"Irrig. Drain. Syst"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"461","DOI":"10.1007\/s00271-010-0207-7","article-title":"Performance assessment of an irrigation scheme using indicators determined with remote sensing techniques","volume":"28","author":"Santos","year":"2010","journal-title":"Irrig. Sci"},{"key":"ref_12","first-page":"419","article-title":"Operational irrigation services from remote sensing: The irrigation advisory plan for the Campania region, Italy","volume":"352","author":"Neale","year":"2012","journal-title":"Remote Sensing and Hydrology"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"771","DOI":"10.5194\/hess-15-771-2011","article-title":"Evapotranspiration modelling at large scale using near\u2013real time MSG SEVIRI derived data","volume":"15","author":"Ghilain","year":"2011","journal-title":"Hydrol. Earth Syst. Sci"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"381","DOI":"10.1175\/BAMS-85-3-381","article-title":"The Global Land Data Assimilation System","volume":"85","author":"Rodell","year":"2004","journal-title":"Bull. Am. Meteorol. Soc"},{"key":"ref_15","unstructured":"Romaguera, M., Salama, S., Krol, M.S., Hoekstra, A.Y., and Su, Z. (2012, January 9\u201313). Synergy between remote sensing ET products and simulated data to retrieve irrigated areas and blue ET in Europe and Africa. Enschede, The Netherlands."},{"key":"ref_16","unstructured":"LSA\u2013SAF (2010). LSA\u2013SAF Validation Report. Products LSA\u201316 (MET), LSA\u201317 (DMET), Network of Satellite Application Facilities. Doc. Num. SAF\/LAND\/RMI\/VR\/0.6; The EUMETSAT."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"386","DOI":"10.1002\/2013WR014194","article-title":"Comparison of prognostic and diagnostic surface flux modeling approaches over the Nile river basin","volume":"50","author":"Yilmaz","year":"2014","journal-title":"Water Resour. Res"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"103","DOI":"10.1016\/S1474-7065(03)00011-1","article-title":"Assessment of climate impact on vegetation dynamics by using remote sensing","volume":"28","author":"Roerink","year":"2003","journal-title":"Phys. Chem. Earth"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"5031","DOI":"10.1080\/01431160210121764","article-title":"Optimal Landsat TM band combinations and vegetation indices for discrimination of six grassland types in eastern Kansas","volume":"23","author":"Price","year":"2002","journal-title":"Int. J. Remote Sens"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"823","DOI":"10.1080\/01431160600746456","article-title":"A survey of image classification methods and techniques for improving classification performance","volume":"28","author":"Lu","year":"2007","journal-title":"Int. J. Remote Sens"},{"key":"ref_21","unstructured":"Tou, J.T., and Gonzalez, R.C. (1974). Pattern Recognition Principles, Addison\u2013Wesley Publishing Company."},{"key":"ref_22","unstructured":"Exelis Visual Information Solutions (2006). ENVI Tutorial: Classification Methods, Exelis Visual Information Solutions."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"237","DOI":"10.1016\/S0167-8655(97)00168-2","article-title":"A new cluster validity index for the fuzzy c\u2013mean","volume":"19","author":"Rezaee","year":"1998","journal-title":"Pattern Recognit. Lett"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1111\/j.2517-6161.1977.tb01600.x","article-title":"Maximum likelihood from incomplete data via the EM algorithm","volume":"39","author":"Dempster","year":"1977","journal-title":"J. R. Stat. Soc. B"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"10","DOI":"10.1145\/1656274.1656278","article-title":"The WEKA data mining software: An update","volume":"11","author":"Hall","year":"2009","journal-title":"Sigkdd Explor"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Richards, J.A., and Jia, X. (1999). Remote Sensing Digital Image Analysis: An Introduction, Springer\u2013Verlag.","DOI":"10.1007\/978-3-662-03978-6"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"7251","DOI":"10.1029\/95JD02165","article-title":"Modeling of land surface evaporation by four schemes and comparison with FIFE observations","volume":"101","author":"Chen","year":"1996","journal-title":"J. Geophys. Res.: Atmos"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"19569","DOI":"10.1029\/1999JD900232","article-title":"A parameterization of snowpack and frozen ground intended for NCEP weather and climate models","volume":"104","author":"Koren","year":"1999","journal-title":"J. Geophys. Res.: Atmos"},{"key":"ref_29","unstructured":"UCLouvain\/ESA (2011). Globcover 2009. Products Description and Validation Report, Paris, France."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1261","DOI":"10.1175\/1520-0442-16.9.1261","article-title":"A global database of land surface parameters at 1\u2013km resolution in meteorological and climate models","volume":"16","author":"Masson","year":"2003","journal-title":"J. Clim"},{"key":"ref_31","unstructured":"Mucher, C.A., Champeaux, J.L., Steinnocher, K.T., Griguolo, S., Wester, K., Heunks, C., Winiwater, W., Kressler, F.P., Goutorbe, J.P., and ten Brink, B. (2001). Development of a Consistent Methodology to Derive Land Cover Information on an European Scale from Remote Sensing for Environmental Modeling, Center for Geo\u2013Information (CGI) Alterra."},{"key":"ref_32","first-page":"1013","article-title":"The IGBP\/DIS global 1\u2013km land\u2013cover data set discover. A project overview","volume":"65","author":"Belward","year":"1999","journal-title":"Photogramm. Eng. Remote Sens"},{"key":"ref_33","unstructured":"Allen, R., Pereira, L.S., Raes, D., and Smith, M. (1998). FAO Irrigation and Drainage Paper N. 56: Crop Evapotranspiration, Food and Agriculture Organization."},{"key":"ref_34","unstructured":"Gellens\u2013Meulenberghs, F., Arboleda, A., and Ghilain, N. (2007). IAHS Symposium on Remote Sensing for Environmental Monitoring and Change Detection, Wallingford, UK."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Monfreda, C., Ramankutty, N., and Foley, J.A. (2008). Farming the planet: 2. Geographic distribution of crop areas, yields, physiological types, and net primary production in the year 2000. Glob. Biogeochem. Cycle.","DOI":"10.1029\/2007GB002947"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Portmann, F.T., Siebert, S., and D\u00f6ll, P. (2010). MIRCA2000\u2013global monthly irrigated and rainfed crop areas around the year 2000: A new high\u2013resolution data set for agricultural and hydrological modeling. Glob. Biogeochem. Cycle.","DOI":"10.1029\/2008GB003435"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"380","DOI":"10.1061\/(ASCE)0733-9437(2007)133:4(380)","article-title":"Satellite\u2013based energy balance for mapping evapotranspiration with internalized calibration (METRIC)\u2013model","volume":"133","author":"Allen","year":"2007","journal-title":"J. Irrig. Drain. Eng"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1607","DOI":"10.5194\/hess-17-1607-2013","article-title":"Estimation of surface energy fluxes under complex terrain of Mt. Qomolangma over the Tibetan plateau","volume":"17","author":"Chen","year":"2013","journal-title":"Hydrol. Earth Syst. Sci"},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Anderson, M.C., Kustas, W.P., and Norman, J.M. (2007). Upscaling flux observations from local to continental scales using thermal remote sensing. Agron. J.","DOI":"10.2134\/agronj2005.0096S"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"3069","DOI":"10.1016\/j.rse.2011.06.009","article-title":"A statistical spatial downscaling algorithm of TRMM precipitation based on NDVI and DEM in the Qaidam basin of China","volume":"115","author":"Jia","year":"2011","journal-title":"Remote Sens. Environ"},{"key":"ref_41","unstructured":"FAO (2009). Aquastat Database, Food and Agriculture Organization. Available online: http:\/\/www.fao.org\/nr\/water\/aquastat\/main\/index.stm."},{"key":"ref_42","doi-asserted-by":"crossref","unstructured":"Romaguera, M., Krol, M.S., Salama, S., Su, Z., and Hoekstra, A.Y. (2014). Application of a remote sensing method for estimating monthly blue water evapotranspiration in irrigated agriculture. Remote Sens, submitted.","DOI":"10.3390\/rs61010033"}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/6\/8\/7026\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:14:08Z","timestamp":1760217248000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/6\/8\/7026"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2014,7,29]]},"references-count":42,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2014,8]]}},"alternative-id":["rs6087026"],"URL":"https:\/\/doi.org\/10.3390\/rs6087026","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2014,7,29]]}}}