AIRBORNE SOIL MOISTURE DETERMINATION USING A DATA FUSION APPROACH AT REGIONAL LEVEL Francisco Martín 1 , Juan Fernando Marchan 1 , Albert Aguasca 2 , Mercedes Vall-llossera 2 , Jordi Corbera 1 , Adriano Camps 2 , Maria Piles 3 , Luca Pipia 4 , Anna Tardà 4 , Alberto G. Villafranca 1 1 Catalan Earth Observation Program – Institut Cartogràfic de Catalunya 2 Remote Sensing Lab – Universitat Politècnica de Catalunya and IEEC/CRAE-UPC 3 SMOS Barcelona Expert Center, Pg. Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain 4 Remote Sensing Area – Institut Cartogràfic de Catalunya ABSTRACT HUMID is a regional level airborne soil moisture mission. The envisioned product combines two key characteristics. On one hand, it provides robustness in presence of surface roughness and vegetation. On the other hand, it improves the current spatial resolution offered by L-band radiometers using a data fusion approach, where the data from an L-band radiometer developed by the Remote Sensing Lab at the Universitat Politècnica de Catalunya will be combined with data from a thermal and a VNIR hyperspectral sensors from the Institut Cartogràfic de Catalunya. Index Terms—Soil moisture, data fusion, microwave radiometry, VNIR, vegetation indexes, surface temperature 1. INTRODUCTION Water cycle is a capital Earth System process, affecting significantly the continuous exchange of moisture –powered by the energy from the Sun– between oceans, atmosphere and lands. Soil moisture (SM) is a key factor in the water cycle, controlling the exchange of water and heat between the land surface and the atmosphere through evaporation and plant transpiration. Therefore, since SM is related to temperature, humidity and precipitation, its retrieval can significantly improve current meteorological forecasts and hydrological models. Consequently, ESA and NASA have started dedicated missions to study this variable. In November 2 nd , 2010 ESA launched SMOS (Soil Moisture and Ocean Salinity) mission, and NASA has scheduled the launch of SMAP (Soil Moisture Active and Passive) for November of 2014. However, both SMOS and SMAP missions are designed for global applications, focusing mainly on a better understanding of climate change. In this scenario PCOT (Catalan Earth Observation Program), as a supporting center of the ICC (Institut Cartogràfic de Catalunya) has identified slightly different end-user needs at local/regional level with respect to those required at global level. Thus, HUMID aims for recovering SM at these regional scales, where spatial resolution and accuracy are paramount issues of the end product. Following the ideas proposed to disaggregate SMOS pixels using MODIS VNIR data [1], HUMID is based on a data fusion process, combining a thermal and VNIR hyperspectral sensors with an L-band radiometer. This radiometer has been designed and manufactured by the Remote Sensing Lab (RS_Lab) of the Universitat Politècnica de Catalunya (UPC) (Fig. 1). Figure 1. Thermal and VNIR hyperspectral sensors and radiometer installation onboard ICC airplane 2. DATA The results presented in this paper are based on the flight campaign conducted by ICC over the area of Gimenells (Lleida, 41º39‟21.34‟‟ N, 0º24‟21.25‟‟E) on March 31 th , 2011. The area has a Calcixerolic Xerochript soil with loam texture, where different types of covers are present, from bare soil to forest soils. The predominant vegetated areas are