Richard Ogilvy, British Geological Survey (United Kingdom)
Philip Meldrum, British Geological Survey (United Kingdom)
Oliver Kuras, British Geological Survey (United Kingdom)
Paul Wilkinson, British Geological Survey (United Kingdom)
Jonathan Chambers, British Geological Survey (United Kingdom)
Significant advances have been made in recent times with the non-invasive electrical imaging of the shallow subsurface. These emerging techniques are increasingly used to underpin studies in waste management, contaminated land characterisation and remediation, the sustainable use of groundwater and soils, as well as the detection and mitigation of natural or man-made hazards. This paper will describe some of the research undertaken by leading players in this field, including research in the British Geological Survey, viz:
Electrical Resistivity Tomography (ERT). New survey design and array optimisation schemes have been developed to improve image reconstruction, particularly for 3D cross-hole scanning applications.
Spectral Induced Polarisation (SIP). Laboratory and field studies show that SIP can detect the flow-paths and distribution of Non-Aqueous Phase Liquids (NAPLs) in the complex frequency domain, using differential time-lapse imaging. Advanced 2.5D SIP inversion code has been developed which allows residual NAPL saturation levels to be estimated using the resistivity model and Archies's second equation.
Capacitive Resistivity Imaging (CRI). Non-contacting capacitive electrodes now permit continuous data scans on highly resistive artificial surfaces (such as tarmac and pavement). The integration of CRI with real-time kinematic global positioning systems provides accurate navigation and location recovery at centimetric scale resolution.
Self-Potential Tomography (SPT). SPT is one of the few geophysical techniques that can detect electro-filtration effects associated with fluid flow in the subsurface. SPT could also provide a better understanding of the fundamental triggering mechanisms associated with several types of gravity mass flow.
Automated time-Lapse Electrical Resistivity Tomography (ALERT). ALERT can monitor temporal changes in subsurface electrical properties using permanently installed instrumentation and buried electrode arrays. Sites are interrogated from the office "on demand" using wireless telemetry (GSM, GPRS, internet or satellite), thereby obviating the need for expensive repeat surveys or manual intervention.
Recent advances with ALERT technology could have far-reaching implications for future environmental monitoring, physical hazard prediction, and the understanding of earth processes. Transient processes can now be observed which could not previously be captured by labour-intensive sampling and measuring campaigns. This is increasingly important in the context of climate change, where extreme events such as flooding and drought are impacting on land-use, and anthropogenic activity. Examples will be given for each of the above techniques.