Understanding Aerial Gamma Radiometrics through Proximal Soil Surveys.

Aerial gamma radiometrics data has proven useful for soil resource mapping applications, although its usefulness for the United States is largely unexplored.  Between large physiographic regions, aerial gamma radiometric data generally responds to differences in clay content and parent material type. Within physiographic regions, due in part to the coarse spatial resolution of the data (transect spaced 5-10 km apart and averaged 60-m point spacing), interpretation of aerial gamma radiometric data is difficult. For example, aerial gamma data might show a weak relationship to soil point (pedon-scale) data.  We suspect that gamma radiometric data is responding to soil properties at larger scales and that the relationship would be improved if models incorporated spatial averages of soil properties rather than just point data. In addition to mismatching of scales between the soil properties and that of the sensor, interference by soil moisture should be understood. Thus, our goal is to understand the nature of both the aerial and proximal gamma-ray signals. To that end we explored the use of proximal gamma radiometric sensing to provide information on the appropriate scale of analysis and inform the use of aerial gamma radiometric data for predictions of soil properties within physiographic regions.