UTILIZATION OF AIRBORNE AND IN SITU DATA OBTAINED IN SGP99, SMEX02, CLASIC AND SMAPVEX08 FIELD CAMPAIGNS FOR SMAP SOIL MOISTURE ALGORITHM DEVELOPMENT AND VALIDATION Andreas Colliander 1 , Steven Chan 1 , Simon Yueh 1 , Michael Cosh 2 , Rajat Bindlish 2 , Tom Jackson 2 , Eni Njoku 1 1) Jet Propulsion Laboratory, California Institute of Technology 2) USDA ARS Hydrology and Remote Sensing Lab ABSTRACT Field experiment data sets that include coincident remote sensing measurements and in situ sampling will be valuable in the development and validation of the soil moisture algorithms of the NASA’s future SMAP (Soil Moisture Active and Passive) mission. This paper presents an overview of the field experiment data collected from SGP99, SMEX02, CLASIC and SMAPVEX08 campaigns. Common in these campaigns were observations of the airborne PALS (Passive and Active L- and S-band) instrument, which was developed to acquire radar and radiometer measurements at low frequencies. The combined set of the PALS measurements and ground truth obtained from all these campaigns was under study. The investigation shows that the data set contains a range of soil moisture values collected under a limited number of conditions. The quality of both PALS and ground truth data meets the needs of the SMAP algorithm development and validation. The data set has already made significant impact on the science behind SMAP mission. The areas where complementing of the data would be most beneficial are also discussed. Index Terms— Soil moisture, SMAP (Soil Moisture Active and Passive), SGP99, SMEX02, CLASIC, SMAPVEX08, PALS 1. INTRODUCTION The NASA Soil Moisture Active and Passive (SMAP) mission is dedicated to measurement of global soil moisture and boreal land surface freeze/thaw state [1]. The satellite will carry radar (active) and radiometer (passive) L-band instruments that will perform simultaneous and coincident measurements of the Earth’s surface. The combination of data from the two instruments will allow unprecedented accuracy, spatial resolution and temporal frequency for global mapping of soil moisture and freeze/thaw state. Field experiment data sets that include coincident remote sensing measurements and in situ sampling will be valuable in the development and validation of SMAP soil moisture retrieval algorithms. Several candidate field experiment campaigns were carried out in the United States between 1999 and 2008 using the airborne Passive and Active L- and S-band (PALS) instrument [2]. These included SGP99 in Oklahoma in 1999 [3]; SMEX02 in Iowa in 2002 [4]; CLASIC in Oklahoma in 2007, and SMAPVEX08 in Maryland in 2008. The PALS instrument is a simulator for SMAP in that it includes both passive and active L-band sensors viewing at 40-degree incidence angle. The field campaign data sets include extensive sampling of ground conditions, including soil moisture, soil temperature, vegetation parameters and surface roughness along with soil texture, land cover and crop classification. Previous papers have presented analyses of these field campaign data (e.g. [5] and [6] on SGP99, [7] on SMEX02, [8] and [9] on CLASIC and [10] on SMAPVEX08), but the data from all experiments have not been analyzed and intercompared as a combined set for soil moisture retrieval algorithm development. In this study the overall statistics of the experiment data and ground conditions of the abovementioned campaigns are presented. Furthermore, the consistency and characteristics of the data is evaluated. Finally, the value and impact of the data for SMAP algorithm validation is assessed and future needs of field experiments in light of these data are discussed. 2. FIELD EXPERIMENTS In the following subsections short descriptions of the four field experiments are given. 2.1. SGP99 The SGP99 (1999 Southern Great Plains) experiment [3] in Oklahoma in July 8-14, 1999 was designed to study remote sensing of soil moisture in vegetated terrain. The study aimed to use L-, S- and C-band airborne observations and satellite observations with well characterized ground conditions. The PALS flights were conducted on six days. The landscape of the Little Washita watershed consisted of