Among the remote sensing techniques, the airborne gamma-ray spectrometry has been widely developed for several tens of years (e.g. IAEA, 1991), being nowadays almost systematically surveyed in regional mapping programs, for soil/regolith (e.g. Lacoste et al., 2011), solid geology reconnaissance (e.g. Metelka et al., 2011) or mineral potential assessment (e.g. Shives et al., 2000). Gamma-ray surveys provide maps of concentration in K, U and Th chemical elements at the ground level. These data are primarily sensitive to the mineralogy and geochemistry of the parent material, as well as its weathering products, including residual and transported clays, sand and gravel (e.g. Minty, 1997). In this study, instead of addressing complex concepts such as lithology, we chose to investigate these gamma spectrometric data by mapping parameters of the regolith, which are simple objective quantities. It is known that these parameters of the regolith: density, moisture, chemistry, all influence the natural gamma ray emissions (e.g. IAEA, 2003). Several papers assess correlations between gamma-spectrometric variables and one or few soil parameters including texture (e.g. Taylor et al., 2002), regolith chemical or mineral contents (e.g. Viscarra Rossel et al., 2007), and other soil parameters such as soil depth, total phosphorus or total carbon (e.g. McKenzie and Ryan, 1999).
