Automated time-Lapse Electrical Resistivity (ALERT)

ALERT satellite

We have developed a new 4D electrical imaging system to monitor temporal and spatial changes in subsurface electrical properties. Such changes may be related to changes in fluid flow, hydrochemistry, or saturation levels.

ALERT uses permanent in situ electrode arrays and intelligent instrumentation to remotely capture volumetric images using wireless telemetry (GSM, GPRS, WiFi or satellite telecommunications).

Sites may be interrogated 'on demand' from office-based PCs, thereby avoiding the need for expensive repeat surveys and manual intervention. This development has involved the design of a new instrument, a customised relational database to handle the unprecedented data streams, finite-element numerical modelling and novel time-lapse image reconstruction algorithms.

Case studies

ALERT installation in Spain

2D ERT image of saltwater wedge in Spain

An ALERT system has been installed in the normally dry bed of the River Andarax, Almeria, Spain to monitor the seawater–freshwater interface in the underlying Quaternary aquifer.

The buried electrode array extends for 1.6 km upstream from the shoreline (see Figure 2).

This unmanned ALERT system generates a daily time-lapse image. These images are transmitted automatically to the BGS database using a dedicated network server and web-portal.

The images are providing new insight on the large-scale hydrogeologic property distributions, and the saline interface. The timely detection and imaging of groundwater changes can help regulate pumping and irrigation schemes.


This generic technology has cross-cutting applications for other market sectors, including waste management, the remote time-lapse monitoring of contaminated land remediation, incipient physical hazards (e.g: landslides, cavity development), and the understanding of extreme events such as flooding or drought.

Scientists and engineers can now study transient earth processes at unprecedented sampling rates.


Contact the Geophysical tomography team