The Soil Moisture-Atmosphere Coupling Experiment (SMACEX) was a four-week field campaign conducted in the Walnut Creek Watershed near Ames, Iowa, from June 15 to July 13, 2002. A main focus of SMACEX was investigating the interactions between the atmospheric boundary layer, surface moisture and vegetation states. The NRC Twin Otter atmospheric research aircraft, the Utah State University Piper Seneca remote sensing aircraft, ground-based Lidars, and an array of 14 eddy covariance towers were deployed to study water and energy cycling across the land-atmosphere interface. 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.

During the field campaign the Twin Otter flew missions from June 15 to July 6 totaling 50 project hours. The Twin Otter flew at an altitude of approximately 40 m over six tracks, which ranged in length from 5.7 to 12.2 km. During the first 2-1/2 weeks of the experiment, there were no precipitation events in the project area. Nevertheless, there was vigorous growth by the dominant crops of corn and soybean, with run-averaged mid-day CO₂ uptake increasing from approximately 0.35 mg/m²/s to in excess of 1.3 mg/m²/s, and latent heat fluxes in excess of 300 W/m². During this period, the regional-average Bowen Ratio stabilized near 0.3 on all tracks. Prior to the final two flights, the project area received precipitation ranging from approximately 0.5 to 50 mm from several localized storms, which produced a significant response from the soil-vegetation system, as indicated by the aircraft-measured fluxes. The average Bowen ratio dropped to approximately 0.15, and CO₂ fluxes increased to some of the highest values ever measured by the Twin Otter (> 2 mg/m²/s on one of the tracks).

The paper presents example data from the Twin Otter and the towers, along with preliminary results from intercomparisons that will be used to test the methodologies to bridge the scales of land-atmosphere interaction from local to regional dimensions.