This data set includes sliced soil core moisture data collected during the Soil Moisture Experiment 2002 (SMEX02), conducted during June and July 2002 in the Walnut Creek watershed in south-central Iowa, USA. The study parameters include gravimetric soil moisture (GSM) and bulk soil density. Data were collected manually at two corn and two soybean sites. Data are provided as ASCII text files. ... The same data are available in a Microsoft Excel spreadsheet. All data are available via FTP. These data were collected as part of a validation study for the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). AMSR-E is a mission instrument launched aboard NASA's Aqua Satellite on 04 May 2002. AMSR-E validation studies linked to SMEX are designed to evaluate the accuracy of AMSR-E soil moisture data. Specific validation objectives include assessing and refining soil moisture algorithm performance; verifying soil moisture estimation accuracy; investigating the effects of vegetation, surface temperature, topography, and soil texture on soil moisture accuracy; and determining the regions that are useful for AMSR-E soil moisture measurements.