7/18/2019 GeolSocPoster_MikeYoung

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 Airborne geophysical mapping of environmental features – examples from Northern IrelandM E Young1, J D Appleton2, D Beamish2, R J Cuss2, C L van Dam1, D G Jones2, M K Lahti2, J C H Miles3, B G Rawlins and C Scheib 2.

1 Geological Survey of Nor thern Ireland, Colby House, Stranmillis Court, Bel fast BT9 5BF. Tel: 028 9038 84622 British Geologi cal Survey, Kingsley Dunham Centre, Keywo rth, Nottingham, NG12 5GG. Tel: 0115 93631003 Health Protection Agency, Centre for Radiation, Chemical and Environmental Hazards, Chilton, Didcot, Oxfordshire OX11 0RQ. Tel: 01235 831600

 Acknowledgements

 The Tellus airborne survey was funded by the Department of Enterprise, Trade and Investment and by the EU Building Sustainable Prosperity programme, through the Department of Agriculture and Rural Development.

 Topographic data based upon Ordnance Survey of Northern Ireland’s® data with the permission of the Controller of Her Majesty’s Stationery Office, © Crown copyright and database rights MOU205.

 The Geological Survey of Northern Ireland (GSNI) hascompleted the national low-level airborne geophysical surveyand geochemical sampling campaigns of the Tellus Project.

 The objectives of this project are• to provide a baseline of information against which

to measure future environmental change; • contribute to sustainable land-use planning decisions by

detecting and mapping geological conditions that maybe associated with natural hazards and land drainage;

 • detect and map certain forms of industrial andagricultural contamination and the conditionsunder which these might develop;

• help government to comply with the requirementsof legislation on the assessment and monitoringof natural resources, soils and waters, includingEuropean Framework Directives;

 • advance the development of Northern Ireland’snatural resource industry and provide the basicgeological data and framework for decision-making and development planning.

 The geophysical results provide new insights intoNorthern Ireland’s geology, particularly where bedrockis obscured by overburden. Definition of faults, dykes

and the major volcanic complexes has been improved. The complementary imagery of magnetics, electricalconductivity and radioactivity facilitate mapping ofsoils, rock types and certain anthropogenic effects.

 The results have enabled:• Identification of new areas of enhanced radon potential

by multivariate linear regression analysis of severaldatasets, including the radiometric channels;

 • Map ping of Cs-137 fallout remaining from the 1986Chernobyl accident and nuclear weapons testing;

• Detection of isolated landfills and mapping ofcontaminant plumes from landfills and industrialsites, using radiometric and conductivity results;

• Mapping soil organic carbon by statistical analysisof the radiometric potassium channel;

 • Estimating the thickness of peat fromobserved gamma-ray attenuation.

Survey specifications The survey was flown for GSNI by the Joint Airborne-geoscience Capability, a partnership of the BGS and theGeological Survey of Finland (GTK). The survey was flownwith a De Havilland Twin Otter aircraft, used previously forgeophysical surveys in Finland and purchased in 2004 bythe Natural Environment Research Council. The aircraft isequipped with two magnetometer sensors, 256-channelgamma-ray spectrometer, four-frequency electromagneticsystem, laser altimeter and GPS navigation system.Ground clearance: 56 m (244 m over urban areas)

Line spacing: 200 mLine direction: 345 degreesSampling intervals: magnetics - 7 m approx

  electro-magnetics - 17 m approx  gamma-ray - 70 m approx

Deposition of caesiumRadioactive caesium was deposited over parts of UK afterthe Chernobyl accident in 1986 and during the periodof nuclear weapons testing in 1961–2. The gamma-raypeak of 137Cs at 662 keV was recorded by the survey. The patterns seen in the data are consistent with wetdeposition caused by bands of rain intercepting theChernobyl plume. Comparison of the results with a land-use classification showed that salt marsh areas, forests,natural grassland, pastures and similar classes exhibitedhigher average 137Cs values, although the range of valuesseen falls within that expected for the UK. Aspect andrelief show correlation with the Northern Ireland 137Csdata at a local scale, but not for the entire 137Cs dataset.

Radon risk estimation The probability of houses in Northern Ireland having radonlevels above the guideline value of 200 Bq/m3 is currentlyestimated only from sparse in-house measurementsaveraged over 5 x 5 km grid squares. Multivariatelinear regression has been tested as a more predictiveapproach, using Tellus airborne radiometric data, soilgeochemistry data and digital geology. There is a generallygood agreement between radon maps modelled bythis approach and conventional radon mapping. Thisapproach should facilitate improved radon risk estimation.

Characterising pollution from landfillsLarge landfills, particularly older landfills not underlain bya fluid-retaining membrane, may release contaminatingfluids to groundwater. Airborne magnetic, e lectricalconductivity and radiometric methods may detectpollution downstream of an unprotected site and detectthe surface expression of exposed sites. Anomalieswere detected by the Tellus survey over certain knowndumps. Historically in Northern Ireland, dumps have beenestablished illegally and airborne screening may providea rapid means of screening remote rural areas for these.

Organic carbon in soilRegional governments have a statutory requirementto estimate the volume of organic carbon in the soil. Aspatial analysis showed a strong negative relationshipbetween the airborne radiometric potassium signal andsoil organic carbon sampled on a 2 x 2 km grid acrossNorthern Ireland. As the mineral content of the soildeclines the organic carbon content increases. We canuse the more intensive airborne survey data to reducethe uncertainty in our estimates of soil organic carbon.In the figure the confidence intervals on the estimates(thin black line) when the radiometric survey data areincluded (red and orange lines) are much narrower thanwhen these data are not included (the thick black lines).

PeatPeat covers some 11% of the land surface of NorthernIreland. Knowing its extent and depth is important forreforestation, ecological management and carbon storageestimation. The Tellus airborne gamma-ray amplitudesreduce significantly over areas mapped as peat.Measurements of peat thickness have been comparedwith ground and airborne gamma-ray amplitudes. Earlyresults indicate that the attenuation of gamma radiationmay be correlated with peat thickness, at least overhomogenous geology, to a depth of 4m. With furthercalibration over different types of bedrock, it may befeasible to use airborne gamma-ray surveys to estimateaverage peat thickness over the area of the field of view.

 Airborne geophysical mapping of

environmental features – examples

from Northern Ireland

Total magnetic intensity anomaly 

Low frequency (3 kHz),apparent conductivity 

Digital terrain model

Radiometric ternary image

Bedrock geology 

l n i n u i i u n

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log S/m

 

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Metres

3D model of conductive zones (>55mS/m)

Dalradian section: airborne total

count vs peat thickness

Carboniferous section: hand-

held spectrometer total

count vs peat thickness

Left: Contoured from tie lines; Right: Contoured from flight lines

Western

Northern Ireland

Configuration in 2005 Configuration in 2006