Assessing soil wetness with airborne radiometric data

A valid interpretation model for UK radiometric data requires a joint assessment of both soil and bedrock variations. Although the geological bedrock (the parent material) provides a specific radiogenic level with associated radiochemical attributes, attenuation of the signal level is controlled by soil wetness in conjunction with the density and porosity of the soil cover. Peat soils, in particular, produce readily identifiable attenuation zones. Other soil types are also predicted to attenuate radiometric signal levels but at lower wetness sensitivities. The amount of water stored in the soil is of fundamental importance to agriculture Studies of soil attenuation zones have now been undertaken using a number of modern UK radiometric data sets. Case studies are presented which highlight the procedures and results obtained. A variety of implied increases in wetness, at the scale of the airborne measurements, have been identified across a range of soil types, including those categorized as freely draining. The level of attenuation (and hence wetness scale) remains uncalibrated since ground information on wetness is not generally available at the appropriate scale.