Determination of altitude-dependence of standard spectra and stripping ratios for the GR820 Airborne Gamma Ray Spectrometry

Abstract

NGU's Airborne Gamma Ray Spectrometer system is used both for geological mapping, and for monitoring radioactive materials in the event of nuclear emergencies. Traditional methods of processing spectrometer data use channel windows around the radionuclides of interest; more advanced methods make use of the full spectra information. Such advanced methods require prior knowledge of the dependence of standard spectra with height.\rHeight-dependent measurements have been made using concrete calibration pads, and polythene sheets to simulate the effects of altitude. The height-dependent standard spectra were determined using singular value decomposition and a global inversion scheme. Using the first two eigenimages, together with suitable scaling factors, we were able to recreate the measured height-dependent standard spectra.\rThe height dependence of standard Th, U and K stripping ratios were also calculated from these standard spectra.