Spatial scale and its effects on comparisons of airborne and ground- based gamma-ray spectrometry for mapping environmental radioactivity

E M Scott 1, D C W Sanderson 2, A J Cresswell 2, J J Lang
1 Dept of Statistics, University of Glasgow, Glasgow G12 8QW, UK
2 Scottish Universities Research and Reactor Centre, East Kilbride G75 0QF, UK

Airborne gamma ray spectrometry (AGS) has emerged as an important method for measuring environmental radioactivity (particularly radio caesium (Cs-137)) over wide areas. In early summer of 2002, a number of European AGS teams mapped three large common areas in a European inter- calibration exercise (RESUMÉ 2002). Part of the exercise also involved ground-based teams who conducted soil sampling, in-situ and dose rate measurements in the same areas.  The study design required airborne and ground-based measurements to be taken at three calibration sites (pre-characterised prior to the exercise), three common areas as well as a large composite area.  The three calibration sites had 31 sampling points designed in an expanding hexagonal pattern with more than 500 laboratory measurements being made. The three common areas, X, Y and Z were measured by each of the AGS teams and a set of 42 ground based sites (control points) were defined within the common areas and investigated by in-situ gamma spectrometry, soil sampling and dose rate measurement.  Analysis of the results focussed on an assessment of comparability of the AGS results and on the agreement between the AGS and ground based results.     The statistical issues in the analysis of the exercise results include the spatial resolution of the measurements made using the different measurement systems and the substantial natural variation compounded with the variation in measurement techniques (and the importance of the spatial  (lateral) homogeneity of the source of the radioactivity).

Keywords:  mapping, spatial scale

In: McRoberts, R. et al. (eds).  Proceedings of the joint meeting of The 6th International Symposium On Spatial Accuracy Assessment In Natural Resources and Environmental Sciences and The 15th Annual Conference of The International Environmetrics Society, June 28 – July 1 2004, Portland, Maine, USA.

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