**2.2. Iowa study area in the SMEX'02 experiment**

SMEX'02 is a remote sensing experiment that was carried out in Iowa in 2002. The main site, chosen for soil moisture, vegetation and surface roughness measurements, was the Walnut Creek watershed, where 32 fields, 10 soybean and 21 corn fields, were sampled intensively [32]. The field and sensor data acquired during this experiment are particularly suitable thanks to the significant number of surveyed fields and wide range of soil conditions. The AirSAR images (resolution: 8-12 m ground range) were acquired on 1, 5, 7, 8, 9 July 2002. The five P-, L-and C-band images were processed by the AirSAR operational processor providing calibrated data sets.
