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A geomatics approach to the interpretation of Ground Penetrating Radar (GPR)


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Presentation to Dept. of Geogrpahy, Queen Mary University of London. Use of 3d visualisation and Geomatics techniques to support interpretation of GPR data.

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A geomatics approach to the interpretation of Ground Penetrating Radar (GPR)

  1. 1. " The challenges associated with Ground Penetrating Radar (GPR) investigations of the Pleistocene fluvial sequences in the Upper Thames and the role that geomatic techniques play in overcoming them.” Stuart Glenday Department of Geography Queen Mary, University of London, Mile End Road LONDON E1 4NS [email_address]
  2. 2. Definition 1: Geomatics <ul><li>“ acquisition, modelling, analysis, and management of spatially referenced data” </li></ul>
  3. 3. Definition 2: GPR <ul><li>Applied Radar. 25 -1000MHZ. </li></ul><ul><li>Dielectric permittivity “ε” controls behavior of radar waves in subsurface </li></ul><ul><li>When radar wave encounter contrast in “ε” , proportion of energy is reflected. </li></ul><ul><li>In the vadose zone subsurface “ε” dominated by capillary moisture content. </li></ul><ul><li>Capillary context function of the ‘texture’ of the sediment. </li></ul><ul><li>Textures related to primary sedimentary structures and facies. </li></ul>
  4. 4. Examples
  5. 5. Definition 3: Pleistocene of the Upper Thames
  6. 6. Research potential in Upper Thames <ul><li>Upper Thames </li></ul><ul><ul><li>Additional terrace subdivisions </li></ul></ul><ul><ul><li>Dating evidence indicates difference in stratigraphic development </li></ul></ul><ul><ul><ul><li>MIS7 directly overlain by MIS2 at Latton. (Lewis et al., 2006) </li></ul></ul></ul><ul><ul><li>Potential Alluvial Fan development? </li></ul></ul><ul><li>Scope for directed research using “traditional” methods is limited </li></ul><ul><ul><li>Relies on serendipitous availability of sediment exposure in quarries </li></ul></ul><ul><ul><li>Limits on scale of investigations </li></ul></ul><ul><li>GPR potential to overcome these issues, especially when used in conjunction with Geomatic technologies </li></ul>
  7. 7. Project conception – Geomatics “Bread and Butter” <ul><li>Geomatics has played a role in overcoming challenges during project conception and planning </li></ul><ul><ul><li>Spatial compilation of diverse information types </li></ul></ul><ul><ul><li>Similar approach to BRITICE compilation of glacial landforms and features related to the last British Ice Sheet </li></ul></ul><ul><li>Pinpoint field area </li></ul><ul><ul><li>Identified as possible alluvial fan </li></ul></ul><ul><ul><li>Sequence diversity > potential to test stratigraphic relationships </li></ul></ul><ul><ul><li>Practical considerations & access </li></ul></ul>
  8. 8. Interpreting Results <ul><ul><li>Coarse gravel component </li></ul></ul><ul><ul><ul><li>Scattering and attenuation </li></ul></ul></ul><ul><li>Poor response due to: </li></ul><ul><ul><li>Presence of clays </li></ul></ul><ul><ul><ul><li>Soil & Subsoil, Component of sediment matrix </li></ul></ul></ul><ul><li>Initial results “Cryptic” </li></ul>se nature of gravel
  9. 9. Adapted methodology <ul><li>More focussed approach </li></ul><ul><ul><li>Directed investigations in regions where results are more positive </li></ul></ul><ul><ul><li>Collect data as intersecting grids </li></ul></ul><ul><ul><ul><li>Determine the continuity of reflectors and facies </li></ul></ul></ul><ul><ul><ul><li>Understanding of the three-dimensional form of reflectors and facies to aid interpretation. </li></ul></ul></ul><ul><ul><ul><li>Identify signal artefacts </li></ul></ul></ul><ul><ul><li>Integrate with Geo-morphological evidence </li></ul></ul><ul><li>Geomatics facilitates this approach </li></ul>
  10. 10. Spatial data collection <ul><li>GPR cart assembly & real-time display </li></ul><ul><ul><li>Rapid data collection: Lots of data in </li></ul></ul><ul><ul><li>Instant feedback through Digital Video Logger </li></ul></ul><ul><ul><li>Portable GIS </li></ul></ul><ul><li>GPS integration </li></ul><ul><ul><li>X,Y,Z of traces at defined intervals </li></ul></ul><ul><ul><li>RTK-DGPS collects coordinates at cm precision </li></ul></ul>
  11. 11. Spatial Data <ul><li>>130 miles of profiles </li></ul><ul><li>>1 million traces </li></ul>
  12. 12. Comparison of sampling parameters 200Mhz 100 Mhz 200 Mhz
  13. 13. Spatially discrete features?
  14. 14. Discrete channel
  15. 15. Domain Conversion
  16. 16. Continuity of reflectors
  17. 17. Mapping sequence boundaries
  18. 18. Claydon Pike: Survey outline
  19. 19. Claydon Pike: Observations
  20. 20. Exposures
  21. 21. References <ul><li>Lewis, S.G., Maddy, D., Buckingham, C., Coope, G.R., Field, M.H., Keen, D.H., Pike, A.W.G., Roe, D.A., Scaife, R.G., Scott, K. 2006. Pleistocene fluvial sediments, palaeontology and archaeology of the Upper River Thames at Latton, Wiltshire, England. Journal of Quaternary Science , 21 , 181–205. </li></ul>