The SMOS Mediterranean Ecosystem L-Band characterisation EXperiment (MELBEX-I) over natural shrubs

10 páginas, 5 figuras, 7 tablas.In the framework of ESA's SMOS mission (Soil Moisture and Ocean Salinity), many studies have been carried out over different land surface types to model their microwave emission at L-band (1.4 GHz). Results of these studies have been integrated in the emission model L-MEB (L-Band Microwave Emission of the Biosphere), which is the core of the SMOS Level 2 soil moisture retrieval algorithm. The Mediterranean Ecosystem L-Band characterisation EXperiment (MELBEX-I) was carried out at the SMOS validation site near Valencia in autumn 2005. The main objective of MELBEX-I was to calibrate L-MEB over Mediterranean shrub land, as no data were available over this biome. For that purpose, multi-angular and dual polarimetric measurements (H, V) were obtained by the EMIRAD L-band radiometer from a 14-m tower. Results of this study indicate a small and constant impact of vegetation on the microwave emission of shrub land, and L-MEB parameters for shrub land were obtained. In addition, the study highlights the need for calibrating microwave soil roughness, which was found to be constant at the site. Depending on the number of retrieved parameters, soil moisture (SM) near the surface could be estimated with errors between 0.035 m(3) m(-3) (if only SM was retrieved) and 0.057 m(3) m(-3) (if SM, optical depth and a roughness parameter were simultaneously retrieved). Finally, no modelling improvements were observed when coarse estimates of the fraction of exposed rocks were accounted for in the model.This work was carried out within the framework of the projects “Calibration of SMOSMIRAS RadiometerMeasurements and Generation of Maps of Salinity and of Soil Moisture Content. UVEG Part (MIDAS-4/UVEG)”, “ProductValidation,Data Exploitation and Expert Centre for the SMOS Mission. UVEG Part (MIDAS-5/UVEG)”, both from the Spanish Ministry for Education and Science (National Research Programme on Space). It was also supported by the projects “Validation of SMOS Products over Mediterranean Ecosystem Vegetation at the Valencia Anchor Station Reference Area. ESA SMOS Cal/Val Announcement of Opportunities (ID 3252)”, and “COSMOS-II (ESA/CESBIO/University of Cambridge, ESTEC contract 22604/09/NL/CT)”.Peer reviewe