1 SMOS - IC : An alternative SMOS soil moisture and 2 vegetation optical depth product 3

The main goal of the Soil Moisture and Ocean Salinity (SMOS) mission over land surfaces 15 is the production of global maps of soil moisture (SM) and vegetation optical depth (τ) based on 16 multi-angular brightness temperature (TB) measurements at L-band. The operational SMOS Level 17 2 and Level 3 soil moisture algorithms account for different surface effects, such as vegetation 18 opacity and soil roughness at 4 km resolution, in order to produce global retrievals of SM and τ. In 19 this study, we present an alternative SMOS product which was developed by INRA (Institut 20 National de la Recherche Agronomique) and CESBIO (Centre d’Etudes Spatiales de la BIOsphère). 21 This SMOS-INRA-CESBIO (SMOS-IC) product provides daily SM and τ at the global scale and 22 differs from the operational SMOS Level 3 (SMOSL3) product in the treatment of retrievals over 23 heterogeneous pixels. Specifically, SMOS-IC is much simpler and does not account for corrections 24 associated to the antenna pattern and the complex SMOS viewing angle geometry. It considers 25 pixels as homogeneous to avoid uncertainties and errors linked to inconsistent auxiliary data sets 26 which are used to characterize the pixel heterogeneity in the SMOS L3 algorithm. SMOS-IC also 27 differs from the current SMOSL3 product (Version 300, V300) in the values of the effective 28 vegetation scattering albedo (ω) and soil roughness parameters. An inter-comparison is presented 29 in this study based on the use of ECMWF (European Center for Medium range Weather Forecasting) 30 SM outputs and NDVI (Normalized Difference Vegetation Index) from MODIS (Moderate31 Resolution Imaging Spectroradiometer). A 6 year (2010-2015) inter-comparison of the SMOS 32 products SMOS-IC and SMOSL3 SM (V300) with ECMWF SM yielded higher correlations and lower 33 ubRMSD (unbiased root mean square difference) for SMOS-IC over most of the pixels. In terms of 34 τ, SMOS-IC τ was found to be better correlated to MODIS NDVI in most regions of the globe, with 35 the exception of the Amazonian basin and of the northern mid-latitudes. 36