GReTA Permanent Geo-Resistivity Monitoring System
G.Re.T.A. is the most effective and innovative solution for Permanent Geo-electric Monitoring of the conditions of large sections of soil. The device is an easy to install industrialised off-the-shelf solution for geo-electrical monitoring. This instrument measures the alteration over time of the soil’s resistivity section, functional to the characterisation of the same in terms of water content, presence of pollutants, cavities and other anomalies.
A consolidated technology
Electrical Resistivity Tomography (ERT) is based on the insertion of an electric field in the ground through electrodes (input electrodes), and the measurement of the voltage through other electrodes (measurement electrodes). From the measure of the voltage it is possible to obtain, through the second law of Ohm, the resistivity value, a peculiar characteristic of all materials.
Overview of GReTA Permanent Geo-Resistivity Monitoring
GReTA is a permanent geo-resistivity monitoring system that automates Wenner-type electrical resistivity tests along an array of 48 electrodes. Once installed, the system operates continuously, producing time-lapse resistivity profiles without the need for repeated field intervention.
This permanent installation allows engineers to distinguish seasonal variations from more significant subsurface changes that may indicate developing issues requiring corrective action
GReTA Field Components
Electrode Cables: Electrode cables are typically embedded permanently in shallow trenches. Electrodes have 1, 2, 3, or 5 meter spacing. Thin stainless steel contact plates are attached to the electrodes at installation time.
Acquisition Unit: The acquisition unit includes a controller with noise filtering and a communications module that sends measurements to the cloud.
Power Unit: The unit has four step-up transformers to supply the required voltages for testing, a battery, and a charging module for a solar panel.
GReTA Cloud Component
The Cloud component processes the survey data and provides visualization via a website. Features include:
- Geo-localization of the installed systems.
- Comparison of measurements over different periods of time with simple and intuitive graphic models.
- The display of additional environmental and piezometric data if available.
- Water content calculation.
- Automated alarm messages when preset thresholds are crossed. Thresholds can be based on % change or absolute values.
GReTA Specifications
Current Injection Circuit
Number of channels: 48 electrodes. Current modulation: 0.001 to 0.4 A. Resolution > 120 μA.
Current Measurement
Resolution: 1 μA. Stability: 0.0025% VM. Accuracy: > 60 μA.
Electrode Voltage Measurement
Automatic scale change.
Automatic filtering: 50 and 60 Hz. Input impedance: 1.6 * 1010 Ω.
± 0.47V Scale
• Resolution: 1 μV.
• Stability > 0,12% VM.
• Accuracy: 70 μV.
± 4.7 V ScaleÂ
• Resolution: 10 μV.
• Stability: > 0.03% VM.
• Accuracy: 700 μV.
