Merlin Olivier auteur aut IRD Walker J.P. auteur aut IRD Panciera R. auteur aut IRD Escorihuela M.J. auteur aut IRD Jackson T.J. auteur aut IRD text journalArticle eng The spatial and temporal invariance of Soil Moisture and Ocean Salinity (SMOS) forward model parameters for soil moisture retrieval was assessed at 1-km resolution on a diurnal basis with data from the National Airborne Field Experiment 2006. The approach used was to apply the SMOS default parameters uniformly over 27 1-km validation pixels, retrieve soil moisture from the airborne observations, and then to interpret the differences between airborne and ground estimates in terms of land use, parameter variability, and sensing depth. For pastures ( 17 pixels) and nonirrigated crops ( 5 pixels), the root mean square error (rmse) was 0.03 volumetric (vol./vol.) soil moisture with a bias of 0.004 vol./vol. For pixels dominated by irrigated crops ( 5 pixels), the rmse was 0.10 vol./vol., and the bias was -0.09 vol./vol. The correlation coefficient between bias in irrigated areas and the 1-km field soil moisture variability was found to be 0.73, which suggests either 1) an increase of the soil dielectric roughness ( up to about one) associated with small-scale heterogeneity of soil moisture or/and 2) a difference in sensing depth between an L-band radiometer and the in situ measurements, combined with a strong vertical gradient of soil moisture in the top 6 cm of the soil. specialized Airborne experiment calibration L-band radiometry National Airborne Field Experiment (NAFE) retrieval algorithm soil moisture Soil Moisture and Ocean Salinity (SMOS) 126 032 6 4 635-639 2009 1545-598X https://www.documentation.ird.fr/hor/PAR00004279 10.1109/lgrs.2009.2012727 1545-598X https://www.documentation.ird.fr/hor/PAR00004279 IRD - Base Horizon / Pleins textes 2009-12-03 2017-08-23 PAR00004279 fre