Airborne geophysical mapping of environmental features - examples from Northern Ireland

Abstract

The Geological Survey of Northern Ireland completed a low-level regional airborne geophysical survey of Northern Ireland during 2005-6 as part of the Tellus Project. The survey was flown by the Joint Airborne Geoscience Capability, a partnership of the British Geological Survey and the Geological Survey of Finland. The aircraft, a De Havilland Twin Otter, was equipped with two magnetometer sensors, a four-frequency electromagnetic system and a 256-channel gamma-ray spectrometer. The traverse-line interval was 200m. Ground-clearance was 56m over the countryside and 250m over populated areas. The objectives of the survey, which was complemented by ground geochemical sampling, were to promote the sustainable development of natural resources and provide key data for environmental monitoring and management. The geophysical results provide new insights into Northern Ireland’s geology, particularly where bedrock is obscured by overburden. Definition of faults, dykes and the major volcanic complexes has been improved. The complementary imagery of magnetics, electrical conductivity and radioactivity facilitate mapping of soils, rock types and certain anthropogenic effects. The results have enabled: • Identification of new areas of enhanced radon potential by multivariate linear regression analysis of several datasets, including the radiometric channels; • Mapping of Cs-137 fallout remaining from the 1986 Chernobyl accident and nuclear weapons testing; • Detection of isolated landfills and mapping of contaminant plumes from landfills and industrial sites, using radiometric and conductivity results; • Mapping soil organic carbon by statistical analysis of the radiometric potassium channel; • Estimating the thickness of peat from observed gamma-ray attenuation