1.3 AIRCRAFT AND TOWER-MEASURED FLUXES OVER RAPIDLY GROWING CORN AND SOYBEAN CROPS IN CENTRAL IOWA J. I. MacPherson 1* , M. Wolde 1 , W. P. Kustas 2 , and J. H. Prueger 3 1 Institute for Aerospace Research, National Research Council of Canada, Ottawa, Ontario, Canada 2 ARS Hydrology Laboratory, U. S. Dept. of Agriculture, Beltsville, MD, USA 3 Soil Tilth Laboratory, U. S. Dept. of Agriculture, Ames, IA, USA 1. INTRODUCTION The Soil Moisture-Atmosphere Coupling Experi- ment (SMACEX) was a four-week field campaign that significantly expanded the objectives of the Soil Moisture Experiment 2002 (SMEX02). The main objective of SMEX02 was to provide data sets for the development and verification of alter- nate passive microwave soil moisture retrieval algorithms in a region with significant agricultural crops. SMACEX was a boundary layer experiment within SMEX02 that used the NRC Twin Otter atmospheric research aircraft, LIDARS, and an array of 14 flux towers to examine water and energy cycling across the land-atmosphere inter- face. In particular, the aircraft and tower data will form a multi-scale dataset with which to evaluate Land-Atmosphere-Transfer-Schemes (LATS) that have been developed to directly integrate the spatial information provided by remotely sensed data. An overview of SMACEX is presented by Kustas et al. (2003). This paper summarizes the flux aircraft program and presents preliminary data from the aircraft and some of the towers. 2. TWIN OTTER INSTRUMENTATION The NRC Twin Otter atmospheric research aircraft (Figure 1) was instrumented to measure the 3-axis components of atmospheric motion and the fluxes of sensible and latent heat, momentum, CO 2 and ozone. It also carried several remote-sensing instruments that will be used to relate the meas- ured fluxes to surface conditions and to measurements made by the other remote sensing aircraft and satellites used in SMEX02 (experiment plan, http://hydrolab.arsusda.gov/smex02 /). These included a Heitronics KT-19 pyrometer for surface temperature, an Exotech Satellite Simulator oper- ated in the TM mode, a Skye Industries Green- ness Indicator, and radiometers for incident and reflected visible, IR and net radiation. Further details on the aircraft instrumentation and subse- quent processing of the recorded data are presented in MacPherson and Wolde (2002). Fig. 1: NRC Twin Otter atmospheric research aircraft 3. FLIGHT OPERATIONS SMACEX was conducted in the Walnut Creek Watershed southwest of Ames, Iowa. This area is representative of a much larger region in the U.S. Upper Midwest in which the primary crops are Fig. 2: Twin Otter flux lines (green) and SMACEX flux tower locations (numbered red asterisks) -------------------------------------------------------------- * Corresponding Author Address: J. I. MacPherson, Building U-61, NRC, Ottawa, ON, Canada, K1A0R6. e-mail: ian.macpherson@nrc.ca