In a report on measuring techniques for soil mapping, by the University of Wageningen, a review is made of various studies on mapping soil properties by gamma-ray mapping. This report concludes: Reviewing these results, we can conclude that clay content in 0-30 cm depth can be predicted using γ-ray spectrometry with reasonable accuracies in multiple studies. In one study also the coarse sand fraction could be predicted. Other properties have either not been evaluated or returned lesser results in the papers reviewed here.
Since calibration of spectra to textural properties is provenance dependent, calibrations tend to be regionally stable. Therefore, once determined for a region, the calibration can be applied on-the-go to derive soil property information in real-time.
Better sampling of soils
In a project for the university of Wageningen, a pre-scan of a site was made. The university planned to take corings, but needed a specific clay contents from the site. Prior to the coring a MS-2000 gamma-ray spectrometer was used to map the spatial variation of the radionuclides. A regional calibration model (based on an existing dataset from samples taken in other projects) was used to translate the radionuclides maps to clay content. After sampling the results were compared and the predicted lute concentrations only deviated by 0.5%.
Our case study Proximal sensing of clay presents results on mapping soil texture.