The relationship between airborne gamma-ray spectrometry data and soil moisture in forested areas of Sweden

Abstract: Measurements and estimations of soil water content are essential information in many differentfields, however, methods for deriving such data are often limited due to scale/spatial resolution, cost and time efficiency, or the presence of a vegetation cover. This thesis examined the relationship between airborne gamma-ray spectrometry (AGRS) data and soil water content in forested areas. In addition, it assessed the feasibility of using AGRS data to predict relative soil moisture for forestry related applications. The study utilized topography-based models, databased on aerial photography, and point soil moisture measurements, which through statistical approaches were assessed for their relationships to the AGRS data in eleven different studyareas located in Sweden. The analyses indicated statistically significant correlations, of weak to moderate strengths, between the AGRS data and the proxy data for soil water content. Also, all analyses indicated that the data from the channels related to potassium-40 decay events (γK) exhibited the strongest relationship to the soil water content proxies. Furthermore, considering the contributing area of an AGRS measurement and also the results obtained in this study, it is suggested that the AGRS data would work better as a predictor of soil moisture regimes on an intermediate to large scale, compared to a smaller scale. At last, although there were limitations to the data used as proxies for soil water content, the analyses suggested that the AGRS data on its own might not be a strong predictor of relative spatial variation in soil moisture. It may however, hold information useful as ancillary data in other methods, as well as hold individualdata points usable for indicating wet areas.