The EuroSTARRS airborne campaign in support of the SMOS mission: first results over land surfaces

Abstract

A number of experiments using ground-based and airborne sensors have shown the high potential of L-band passive microwave radiometry for estimating and monitoring surface soil moisture. This has led to the Soil Moisture and Ocean Salinity (SMOS) mission, a European Space Agency (ESA) Earth Explorer Opportunity mission. SMOS has the objective to observe soil moisture over land and sea surface salinity over sea, both key parameters for atmospheric, oceanographic and hydrological predictive models. In preparation of SMOS, the EuroSTARRS airborne campaign was carried out in November 2001. Multi-angular measurements of the surface brightness temperature at L-band (1.4 GHz) at vertical polarization were acquired by the ‘Salinity Temperature and Roughness Remote Scanner’ (STARRS) radiometer from the Naval Research Laboratory (NRL, USA) over several sites in Southern France, the Pyrenees and Eastern Spain. The chosen sites represent specific land conditions and vegetation canopies where microwave surface emission models need further investigation, and include: dense forests, shrubs and scrubland, mixed areas of different vegetation covers and areas with variable topography. This paper gives an overview of the experiment, including a discussion of the objectives, description of the sites, details of the microwave measurements and some first results of the campaign. First, a principal component analysis of the forest brightness temperature measured at different configurations illustrates the sensitivity of brightness temperature to biomass conditions for coniferous trees. Then, the microwave signature of the vegetation covers considered in this study—coniferous forest at Les Landes (France), mixed deciduous/coniferous stands at the Agre forest (France), shrubland, vineyards and orchards at the Valencia site (Spain)—is illustrated, in particular as regards to the dependence of the L-band emissivity to biomass conditions.