Imaging of geochemical data, by BGS NI
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Transcript of Imaging of geochemical data, by BGS NI
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TalkingWith Maps
2010
Imaging of geochemical data by interpolation within geological boundaries
Don Appleton (British Geological Survey)
Presented by Claire McGinn (Geological Survey of Northern Ireland)
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TalkingWith Maps
2010Acknowledgements
This work is based on research using a VB.Net tool compiled for ArcGIS 9.3 by Keith Adlam (BGS)
Data for this work were provided by the Tellus Project, funded by the Department of Enterprise, Trade and Investment of Northern Ireland.
The contributions of GSNI and BGS staff who collected, prepared and analysed the Tellus soil samples is gratefully acknowledged.
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TalkingWith Maps
2010
Area: 14,000km2
Northern Ireland
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TalkingWith Maps
2010
Tellus Project: Northern Ireland Soil data
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TalkingWith Maps
2010
Who uses Tellus data?
• Environmental Agencies• Commercial Industries• Marine Scientists• Agricultural Departments• Universities• Local Councils• Regulatory Authorities
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TalkingWith Maps
2010
Potentially Harmful Elements (PHE)
• Arsenic (As)• Cadmium (Cd)• Chromium (Cr)• Lead (Pb)
Nickel (Ni) in soils
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TalkingWith Maps
2010
Gridding by Inverse Distance Weighting: Chromium
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TalkingWith Maps
2010
Simplified Bedrock Geology Map
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TalkingWith Maps
2010 Methodologies
Inverse Distance Weighting
versus
Soil Parent Material (i.e. within geological boundaries)
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TalkingWith Maps
2010
Bedrock geology boundaries
Superficial geology boundaries
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TalkingWith Maps
2010
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TalkingWith Maps
2010
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TalkingWith Maps
2010
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TalkingWith Maps
2010
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TalkingWith Maps
2010
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TalkingWith Maps
2010
3
2
2
34
2
44
43
4+4+4+3+2=17
17/5=3.4
4+3+3+2+2=14
14/5=2.8
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TalkingWith Maps
2010
4+4+4+3+2=17
17/5=3.4
4+3+3+2+2=14
14/5=2.8
1-2.93-4.95-6.97-8.9
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TalkingWith Maps
2010
4+4+4+3+2=17
17/5=3.4
4+3+3+2+2=14
14/5=2.8
1-2.93-4.95-6.97-8.9
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TalkingWith Maps
2010
Step 1: Geology polygons are intersected with the 1km GridStep 2: Centroids are created for each geological polygon within each 1km polygonStep 3: VB.Net Tool identifies the nearest 5 soil sites to the centroidfor the Parent material and superficial geology
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TalkingWith Maps
2010
Rasterised image of the centroidsinterpolated within parent material boundaries
Sample points and centroids(Parent material method )
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TalkingWith Maps
2010
Chromium in soils
New Parent Material mapping
Old method using IDW mapping.
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TalkingWith Maps
2010
Parent Material soil chemistry maps: optimum number of samples for Parent Material mapping
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 5 10 15 20 25
Number of neighbouring samples
MSD
As AVCr AVNi AVPb AVAverage of As, Cr, Ni, Pb AVOverall average ALR-GALA
( )2
1
measured estimatedn1 MSD ∑
=
−=n
i
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TalkingWith Maps
2010
Evaluation of Parent Material and IDW soil chemistry mapping using holdout validation
Element Spatial analyst IDW
Parent Material mapping (GM)
Parent Material mapping (IDW GM)
As 0.18 0.15 0.16Cr 0.43 0.31 0.31Pb 0.20 0.19 0.21
Mean squared deviation (MSD) for As, Cr and Pb for the three mapping methods based on combining the results for two 10% holdout subsets. Lowest MSD values for each element indicated in bold type. (Lne data).
( )2
1
measured estimatedn1 MSD ∑
=
−=n
i
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TalkingWith Maps
2010
Chromium in soils – all NI
New regional Parent Material mapping.
Old version using IDW
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TalkingWith Maps
2010
Nickel above Soil Guideline Values (SGV)Residential 130 mg/kg; Allotments 230 mg/kg
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TalkingWith Maps
2010
Arsenic above Soil Guideline ValuesResidential 32 mg/kg; Allotments 43 mg/kg
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TalkingWith Maps
2010
For more information
Contact GSNI: [email protected]
GeoIndex:http://maps.bgs.ac.uk/gsni_geoindex/