Wednesday, 22 April 2015

Groundhog explores deep beneath our feet... by Gerry Wildman

To cope with 21st century issues like rapidly expanding cities and demands for natural resources we need clever 21st century solutions. 'Groundhog' is a new digital tool from the BGS which delivers 3D geological models to communities, planners and policy makers. It allows users to understand the issues and solutions that literally lay at their feet. Gerry Wildman, Data and Science Services Manager, explains more...

Geology is a phenomenon that changes at depth. Layers of rock are built up on top of each other over vast quantities of time.  These layers are then subjected to stresses and strains, which fold, fault and deform the ground. Through geological time, older rock layers may be ground down by erosion before younger layers are deposited on top. When considering the geology, it’s important to look not only at the type of the geology you find at the surface, but also how and when this changes at depth. Knowing how these layers change is important in understanding how we can use the ground. For example it can help us to understand where groundwater can flow, where the natural resources are, and what to consider when designing buildings and structures above and below the ground. 

Over the last decade many Geological Surveys across the world, including BGS, have begun to communicate their geological understanding of the ‘subsurface’ through 3D geological models. BGS now has a number of different 3D  geological models ranging from a national resolution ‘fence diagram’ model of the onshore bedrock geology: the GB3D  bedrock model to shallow, local-scale models,  typically for use in ground investigations, groundwater studies and tunnelling projects.

London Geological Model
Recently, BGS has begun releasing data from a selection of their local-scale models in their Groundhog system. Developed by BGS, Groundhog is a tool that is used to deliver geological models over the web. It allows the user to explore the 3D models by creating ‘virtual boreholes’ or ‘virtual sections’.  Groundhog delivers the results straight to the user as pdf reports. Currently 3D models for London, Manchester and part of Suffolk are available in this system, with more planned.

The ethos behind Groundhog is to provide a service that conveys complicated geology in a simple way. As it runs in a web browser, it removes the need for expensive and specialised software, enabling anyone to use the models. But behind the simplicity is some very clever stuff. In creating the underlying models BGS uses a range of methods to capture our geological understanding varying from direct interpretations by geologists to semi-automated modelling involving advanced maths. The methods used depend on the geological situation and how much data is available. Each model takes account of existing BGS experience and data that may include our vast collections of borehole logs, seismic lines and regional geophysical data.

Screenshot from Groundhog, visit here
To enable Groundhog to produce virtual boreholes and sections, the models are represented behind the scenes as a stack of 2D elevation grids, each grid representing the stratigraphic base of one geological layer, and a further grid to represent the ground surface (the digital terrain model, DTM).  The grids are then converted to a binary format for use in Groundhog making them much quicker for the drawing tool to access the required data points within them.  A simple database provides an index to the available models and their grid file and fault file layers. By querying a stack of grids for a given X,Y position on a map, Groundhog can create a vertical log through the 3D model.  A series of vertical logs along a specified line can be used to create a cross-section. By considering a collection of vertical logs sampled on a 2D grid with respect to a fixed or DTM-relative elevation value, a horizontal slice can also be produced.

For more information, or to order your own virtual borehole or section, please see our website. Every Wednesday throughout April and May 2015 Groundhog reports are half price, follow #3Dgroundhog on Twitter for more links and info.


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