Assessing site suitability for Scots pine using airborne and terrestrial gamma-ray measurements in Finnish Lapland

Low-altitude airborne gamma-ray (AGR) data, obtained with the aircraft-mounted 25-l NaJ(Tl) gamma spectrometer and interpolated into a 50 × 50 m pixel size, over 1200 km2 of glaciated terrain in Finnish Lapland, were applied to classify and interpret site suitability for Scots pine (Pinus sylvestris L.). The selection of the training and validation sets for the classification of AGR data was based on the forest management history and soil moisture content (θv) determined by dielectric (e) measurements. The ground calibration measurements showed a significant negative correlation between the soil e (i.e., θv) and terrestrial gamma-ray flux (TGR-γ) from potassium (γK) and thorium decay series (γTh), suggesting that the attenuation of gamma flux is due to soil θv. Both ground and airborne surveys indicated that γK was significantly higher in drift of Scots pine stands than in drift of Norway spruce (Picea abies (L.) Karst.) stands. Out of four tested combinations of the AGR channels, i.e., (i) potassium (K),...