Comparison of airborne and terrestrial gamma spectrometry measurements - evaluation of three areas in southern Sweden

Journal of Environmental Radioactivity

2013

This study considers gamma ray attenuation in relation to the soils and bedrock of Northern Ireland using simple theory and data from a high resolution airborne survey. The bedrock is considered as a source of radiogenic material acting as parent to the soil. Attenuation in the near-surface is then controlled by water content in conjunction with the porosity and density of the soil cover. The Total Count radiometric data together with 1:250k mapping of the soils and bedrock of Northern Ireland are used to perform statistical analyses emphasising the nature of the low count behaviour. Estimations of the bedrock response characteristics are improved by excluding areas covered by low count soils (organic/humic). Equally, estimations of soil response characteristics are improved by excluding areas underlain by low count bedrock (basalt). When the spatial characteristics of the soilclassified data are examined in detail, the low values form spatially-coherent zones (natural clusters) that can potentially be interpreted as areas of increased water content for each soil type. As predicted by theory, the highest attenuation factors are associated with the three organic soil types studied here. Peat, in particular, is remarkably skewed to low count behaviour in its radiometric response. Two detailed studies of blanket bogs reveal the extent to which peat may be mapped by its radiometric response while the intra-peat variations in the observed response may indicate areas of thin cover together with areas of increased water content.

Section: Airborne Radiometric Datamentioning

confidence: 99%

Gamma ray attenuation in the soils of Northern Ireland, with special reference to peat

Journal of Environmental Radioactivity

2013

Section: The Airborne Surveymentioning

confidence: 99%

Airborne geophysics: a novel approach to assist hydrogeological investigations at groundwater-dependent wetlands

Farr

2013

QJEGH

Abstract:This paper provides an assessment of existing airborne baseline geophysical data in relation to the hydrogeological characterisation of protected groundwater dependant terrestrial ecosystems (wetlands) found on Anglesey, Wales. The attenuation of the radiometric data identifies the main areas of water saturation in the very near surface. The radiometric data have the potential to identify additional areas where similar degrees of saturation exist. The data may therefore be used to help define extensions to existing site boundaries and to provide information in the assessment of new wetland areas. The radiometric data also show regional scale transition from the Carboniferous Limestone in the east, important for water supply to the wetlands, to older more impermeable strata to the west. The conductivity data appear capable of mapping the lateral extent of clay accumulations, concealed below peat cover which can act as a confining layer to the bedrock aquifer. At the regional scale the data reveal the extent of a former Holocene lake system and the hydrogeological control of a Carboniferous limestone/sandstone contact. The data therefore provide a non-invasive spatially-continuous, characterisation of the sites, improving the understanding of their dynamic water balances and, potentially, guiding further ground assessments and invasive investigations.

“…The ground area or footprint, which contributes radioactivity to each 1-s measurement, was assessed by Pitkin and Duval (1980). For a stationary measurement, at a height of 60 m, 90 % of the airborne response will be provided across a circle of radius 160-180 m (Kock and Samuelsson 2011).…”

Section: Airborne Radiometric Datamentioning

confidence: 99%

The Cornubian geothermal province: heat production and flow in SW England: estimates from boreholes and airborne gamma-ray measurements

Busby

2016

Geotherm Energy

The Cornubian granite batholith provides one of the main high heat production and flow provinces within the UK. An extensive programme of borehole measurements was undertaken in the 1980s to characterise the geothermal resource. Here we revisit the published data on heat flow and heat production from 34 boreholes and revise the published heat flow values in accord with modern palaeoclimate knowledge. This leads to a more rigorous (and increased) set of estimated temperatures at depth across the granite outcrops. Predicted temperatures at a depth of 5 km largely exceed 200 °C and are 6-11 % higher than previously estimated values. We also reconsider the borehole heat production values in conjunction with new heat generation information from a recent regional-scale airborne geophysical survey. The radiometric (gammaray) data provide detailed (~70 m along-line) ground concentration estimates of the heat-producing radioelements. These are then combined to estimate heat production in the near surface. The airborne estimates are subject to attenuation by the soil profile. Here we demonstrate and then adopt an assumption that the observations of the soilbedrock medium undergo a flux attenuation by a factor of about two compared to the response of the underlying material. The revised estimates are then correlated with their equivalent deeper borehole estimates. Linear regression is then used to correct the shallow airborne estimates to values that are consistent with the deeper borehole determinations. The procedure provides a detailed and extensive mapping of heat production at both on-and off-granite locations across SW England. The Dartmoor and Land's End granite offer the greatest spatial geothermal potential in terms of their intrinsic radionuclide concentrations and associated heat production. District-scale heat production is studied using the airborne data acquired uniformly across conurbations. The analysis identifies the towns of Camborne, Penzance, St. Austell, Redruth and St Ives as having relatively high values (>4 μW m −3 ) within their urban perimeters.