The Soil Moisture Experiment 2002 (SMEX02) was held in a 50 km by 100 km region surrounding Ames, Iowa, USA, between June 24 and July 12, 2002. The experiment had several objectives, including aircraft testing of new soil moisture sensor technologies, extension of soil moisture inversion algorithms to a broad range of vegetation conditions, and validation of soil moisture retrievals from the AMSR-E satellite on the NASA EOS Aqua platform. To satisfy these multiple objectives, a comprehensive ground-truth plan was implemented. Surface soil moisture content was measured daily at 81 sites using portable impedance probes and gravimetric data for probe validation. Thirty-three of these sites were located within the Walnut Creek watershed, while the remaining 48 were evenly-spaced along 4 N-S transects. In this presentation we characterize soil moisture variability within the entire region and its subregions, including the Walnut Creek watershed and AMSR-E footprints. Particular attention is paid to the temporal evolution of soil moisture variability and its behavior across scales.