The effect of flight line spacing on radioactivity inventory and spatial feature characteristics of airborne gamma‐ray spectrometry data

Abstract

Airborne Gamma Spectrometry (AGS) is well suited to the mapping of radioactivity in the environment. Flight parameters (e.g. speed and line spacing) directly affect the rate of area coverage, cost, and data quality of any survey. The influences of line spacing have been investigated for data from inter‐tidal, coastal and upland environments with a range of ¹³⁷Cs activity concentrations and depositional histories. Estimates of the integrated ¹³⁷Cs activity (‘inventory’) within specified areas and the shapes of depositional features were calculated for subsets of the data at different line spacings. Features with dimensions greater than the line spacing show variations in inventory and area of less than 3%, and features with dimensions less than the line spacing show larger variations and a decreased probability of detection. The choice of line spacing for a task is dependent on the dimensions of the features of interest and required edge definition. Options for line spacing for different tasks are suggested. It is noted that for regional mapping, even 5–10 km line spacing can produce useful data.

Acknowledgements

The work presented here was funded by the Department of Transport, Environment and the Regions (DETR), the Environment Agency (EA), the Ministry of Agriculture, Fisheries and Food (MAFF), British Nuclear Fuels Ltd (BNFL), the Industry Management Committee (IMC), and the SNIFFER fund.

The aircraft used for the fieldwork was supplied by PDG Helicopters Ltd, and flown mostly by John Constable, with a few hours flown by Ivor Griffiths. True‐colour composite and classified satellite imagery were produced by Dr Andrew Tyler and Paula Atkin of the Department of Environmental Science, University of Stirling. Liquid nitrogen for cryogenic cooling of the Ge detectors was supplied by Dr Paul McDonald of the Westlakes Research Institute. Iona Anthony, Iain Houston, and Anne Sommerville assisted with the fieldwork.