Optical, Thermal and L-Band Sinergies at high Spatial Resolution to Improve SMOS-Derived Soil Moisture Maps
Sanchez, Nilda¹; Martinez-Fernandez, Jose¹; Piles, Maria²; Vall-llosera, Merce²; Camps, Adriano²; Sanchez-Ruiz, Sergio¹; Herrero-Jimenez, Carlos¹; Gumuzzio, Angela^1
1Universidad de Salamanca, SPAIN; ²UPC, SPAIN

The ESA’s Soil Moisture and Ocean Salinity (SMOS) mission provides soil moisture maps at 40-km spatial resolution and a revisit of less than 3 days. Nowadays the scientific community is conducting efforts to improve this limited resolution through different downscaling perspectives. Several approaches have been developed to obtain SMOS soil moisture maps at 1 km resolution. One of these methodologies uses a regression analysis relating soil moisture reference data (SMOS L2 product) to MODIS Land Surface Temperature (LST), MODIS Normalized Difference Vegetation Index (NDVI) and SMOS brightness temperatures (TB) [1]. Under the same context, a field campaign over the SMOS Cal/Val site in Spain (the Soil Moisture Measurement Stations Network, REMEDHUS) was performed in summer, 2012, including intensive field measurements and airborne observations with optical, thermal and microwave sensors. The sensors on board included the Thermal Airborne Spectrographic Imager (TASI), the Compac Airborne Spectrographic Imager (CASI) and the Airborne RadIomEter at L-band (ARIEL). CASI and TASI, as well as the flight facilities were provided by the Institut Cartográfic de Catalunya, whereas ARIEL was provided by the Universitat Politécnica de Catalunya. In addition, a visible and near-infrared scene from the Deimos-1 mission taken simultaneously over the area and provided by Elecnor-Deimos consortium to the University of Salamanca, completed the dataset. The research is focusing on: 1) Testing the performance of the downscaling algorithm proposed in [1] at two very high resolutions, i.e., 3.5 m of TASI-CASI and 22 m of Deimos-1. 2) Testing the improvement of the algorithm when using other spectral indices, taking into account the broad spectral capability of CASI. 3) Testing the suitability of using alternative optical sensors for improving the SMOS soil moisture products. The first results suggest that a finer spatial resolution improves the performance of the relationship between spectral index-surface temperature with the observed soil moisture. It was also preliminarily observed that visible (PRI, Photochemical Reflectance Index) and red-edge indices are direct and indirectly, respectively correlated with the soil moisture content, and both of them seemed to be useful for enhancing the downscaling algorithm. [1] M. Piles, A. Camps, M. Vall-llossera, I. Corbella, R. Panciera, C. Rüdiger, Y. Kerr, and J. Walker, “Downscaling SMOSDerived Soil Moisture Using MODIS Visible/Infrared Data,” IEEE Transactions on Geoscience and Remote Sensing, vol. 49, pp. 3156 -3166, 2011.