a geomatics approach to the interpretation of ground penetrating radar (gpr)
DESCRIPTION
Presentation to Dept. of Geogrpahy, Queen Mary University of London. Use of 3d visualisation and Geomatics techniques to support interpretation of GPR data.TRANSCRIPT
"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
http://www.geog.qmul.ac.uk/
Department of GeographyQueen Mary, University of London,Mile End RoadLONDONE1 4NS
Definition 1: Geomatics
“acquisition, modelling, analysis, and management of spatially referenced data”
Definition 2: GPR
• Applied Radar. 25 -1000MHZ.• Dielectric permittivity “ε”
controls behavior of radar waves in subsurface
• When radar wave encounter contrast in “ε” , proportion of energy is reflected.
• In the vadose zone subsurface “ε” dominated by capillary moisture content.
• Capillary context function of the ‘texture’ of the sediment.
• Textures related to primary sedimentary structures and facies.
Examples
Definition 3: Pleistocene of the Upper Thames
Research potential in Upper Thames
• Upper Thames– Additional terrace subdivisions– Dating evidence indicates difference
in stratigraphic development• MIS7 directly overlain by MIS2 at
Latton. (Lewis et al., 2006)– Potential Alluvial Fan development?
• Scope for directed research using “traditional” methods is limited– Relies on serendipitous availability
of sediment exposure in quarries– Limits on scale of investigations
• GPR potential to overcome these issues, especially when used in conjunction with Geomatic technologies
Project conception – Geomatics “Bread and Butter”
• Geomatics has played a role in overcoming challenges during project conception and planning– Spatial compilation of diverse
information types– Similar approach to BRITICE compilation
of glacial landforms and features related to the last British Ice Sheet
• Pinpoint field area– Identified as possible alluvial fan– Sequence diversity > potential to
test stratigraphic relationships– Practical considerations & access
Interpreting Results
– Coarse gravel component• Scattering and attenuation
• Poor response due to:– Presence of clays
• Soil & Subsoil, Component of sediment matrix
• Initial results “Cryptic”
se nature of gravel
Adapted methodology
• More focussed approach– Directed investigations in regions where results
are more positive– Collect data as intersecting grids
• Determine the continuity of reflectors and facies• Understanding of the three-dimensional form of
reflectors and facies to aid interpretation.• Identify signal artefacts
– Integrate with Geo-morphological evidence
• Geomatics facilitates this approach
Spatial data collection
• GPR cart assembly & real-time display– Rapid data collection: Lots of
data in – Instant feedback through
Digital Video Logger– Portable GIS
• GPS integration– X,Y,Z of traces at defined
intervals– RTK-DGPS collects
coordinates at cm precision
Spatial Data
>130 miles of profiles
>1 million traces
Comparison of sampling parameters
200Mhz
Spatially discrete features?
Discrete channel
Domain Conversion
Continuity of reflectors
Mapping sequence boundaries
Claydon Pike: Survey outline
Claydon Pike: Observations
Exposures
References
• 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.