OR/14/030 How the dataset was created

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Entwisle, D C, White, J C, Busby, J P, Lawley R S and Cooke, I L. 2014. Electrical Resistivity Model of Great Britain: User Guide. British geological Survey. (OR/14/030).

Data was collated and interpreted from a number of different sources currently held by BGS. The primary datasets used for the near surface electrical resistivity model of Great Britain are:

  • Parent Material Map V6 dataset.
  • BGS National Geotechnical Properties Database
  • BGS Physical Laboratories Properties Database
  • BRE Stone list (BRE)[1]
  • National Resistivity Soundings Database

Geological classification is undertaken on a lithostratigraphic basis since the age of the sedimentary deposits is a key factor in the parameter attribution. This approach means information from units for which there is a reasonable amount of data can be used to inform the parameterisation of units of similar age and type where there is little or no information available.

The DiGMapPlus dataset is compiled using the following workflow:

  1. Identify characteristics, measurements and observations from archive records relating to the resistivity of surface materials (presence of clay minerals, porosity, saturation, measured resistivity etc).
  2. Identify the Primary lithology (lith1) and secondary lithologies (lith2), where applicable, for each of the LEX-RCS codes found in the Parent Material Dataset.
  3. Assess whether the range of available evidence statistically supports the range of possible classes (using typical tests such as ANOVA), or whether expert judgement is required to complete the parameter data (presence of clay minerals, porosity, saturation, measured resistivity) for the primary/secondary lithologies.
  4. Calculate the 5000 realisations of resistivity using the Berg algorithm for each LEX-RCS code.
  5. Carry out the statistical analysis of the modelling and extract the resistivity values for the desired percentiles.
  6. Compile the spatial (map) by coupling the resitivity values to the soil-parent material map (PMM) of Great Britain (Lawley, 2008[2]) through the shared LEX-RCS code.
  7. Submit data for standard BGS digital-data checking procedures (to assess completeness and cleanliness of content).

Reference

  1. BRE, Stone list. http://projects.bre.co.uk/ConDiv/stonelist/stonelist.html
  2. LAWLEY, R. 2008. The soil-parent material database: a user guide, British Geological Survey Open report, OR/08/034.