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Imaging of geochemical data, by BGS NI

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  • 1. Talking With 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)
  • 2. Talking With Maps Acknowledgements 2010 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.
  • 3. Talking Northern Ireland With Maps 2010 Area: 14,000km2
  • 4. Tellus Project: Northern Ireland Talking With Maps Soil data 2010
  • 5. Talking Who uses Tellus data? With Maps 2010 • Environmental Agencies • Commercial Industries • Marine Scientists • Agricultural Departments • Universities • Local Councils • Regulatory Authorities
  • 6. Talking Potentially Harmful Elements (PHE) With Maps Nickel (Ni) in soils 2010 • Arsenic (As) • Cadmium (Cd) • Chromium (Cr) • Lead (Pb)
  • 7. Gridding by Inverse Distance Talking With Maps Weighting: Chromium 2010
  • 8. Talking Simplified Bedrock Geology Map With Maps 2010
  • 9. Talking With Maps 2010 Methodologies Inverse Distance Weighting versus Soil Parent Material (i.e. within geological boundaries)
  • 10. Talking Bedrock geology With Maps 2010 boundaries Superficial geology boundaries
  • 11. Talking With Maps 2010
  • 12. Talking With Maps 2010
  • 13. Talking With Maps 2010
  • 14. Talking With Maps 2010
  • 15. Talking With Maps 2010
  • 16. 4+4+4+3+2=17 Talking 17/5=3.4 With Maps 2010 3 4 4 4 2 3 2 4 2 3 4+3+3+2+2=14 14/5=2.8
  • 17. 1-2.9 4+4+4+3+2=17 3-4.9 Talking 17/5=3.4 5-6.9 7-8.9 With Maps 2010 4+3+3+2+2=14 14/5=2.8
  • 18. 1-2.9 4+4+4+3+2=17 3-4.9 Talking 17/5=3.4 5-6.9 7-8.9 With Maps 2010 4+3+3+2+2=14 14/5=2.8
  • 19. Talking With Maps 2010 Step 1: Geology polygons are intersected with the 1km Grid Step 2: Centroids are created for each geological polygon within each 1km polygon Step 3: VB.Net Tool identifies the nearest 5 soil sites to the centroid for the Parent material and superficial geology
  • 20. Talking Sample points With Maps and centroids 2010 (Parent material method ) Rasterised image of the centroids interpolated within parent material boundaries
  • 21. Chromium in soils Talking With Maps 2010 New Parent Material mapping Old method using IDW mapping.
  • 22. Parent Material soil chemistry maps: Talking optimum number of samples for Parent With Maps 2010 Material mapping 2 1 n MSD = ∑ (estimated − measured ) n i =1   1.8 As AV 1.6 Cr AV Ni AV 1.4 Pb AV Average of As, Cr, Ni, Pb AV Overall average ALR-GALA 1.2 1 MSD 0.8 0.6 0.4 0.2 0 0 5 10 15 20 25 Number of neighbouring samples
  • 23. Evaluation of Parent Material and IDW Talking soil chemistry mapping using holdout With Maps 2010 validation 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 n MSD = ∑ (estimated − measured ) n i =1 Element Spatial Parent Parent analyst Material Material IDW mapping mapping (GM) (IDW GM) As 0.18 0.15 0.16 Cr 0.43 0.31 0.31 Pb 0.20 0.19 0.21
  • 24. Chromium in Talking soils – all NI With Maps 2010 New regional Parent Material mapping. Old version using IDW
  • 25. Nickel above Soil Guideline Values (SGV) Talking Residential 130 mg/kg; Allotments 230 mg/kg With Maps 2010
  • 26. Arsenic above Soil Guideline Values Talking Residential 32 mg/kg; Allotments 43 mg/kg With Maps 2010
  • 27. Talking With Maps 2010 For more information Contact GSNI: gsni@detini.gov.uk GeoIndex: http://maps.bgs.ac.uk/gsni_geoindex/