What is Vertical Electrical Sounding (VES)?

VES Definition

Vertical Electrical Sounding (VES), also known as Electrical Resistivity Sounding, is a geophysical exploration method used to determine the vertical variation of subsurface resistivity by gradually increasing the electrode spacing.

It is particularly effective for mapping layered geological structures and identifying aquifers, mineral deposits, and contamination plumes.

Technical Methods & Implementation Principles

Electrode Configuration

•     Uses Wenner or Schlumberger array with 4 electrodes (2 current + 2 potential)

•     Example: A 128-electrode system with 0.75m spacing achieves high-density data acquisition

Data Acquisition & Inversion

•     Measures apparent resistivity (ρ) using Ohm’s law:ρ=IΔV⋅K

where K is a geometric factor dependent on electrode spacing.

•     Advanced inversion software (e.g., IPI2WIN) converts raw data into layered resistivity models

Key Benefits of VES

Non-invasive & Cost-effective

•     Requires only surface electrode arrays without drilling.

•     Reduces exploration costs by 40% compared to traditional drilling methods

High Sensitivity to Hydrological Features

•     Detects water content, porosity variations, and salinity gradients (e.g., seawater intrusion monitoring)

Multi-scale Applications

•     Adaptable to depths from 10m to 500m with adjustable electrode spacing

Advantages & Limitations

Pros	Cons
Cost-Effective: 40% lower cost than traditional drilling Multi-Layer Detection: Resolves 6+ geological layers	Depth Resolution: Accuracy decreases by 15% beyond 200m
Field Adaptability: Operates in -40°C to +55°C	Data Complexity: Requires advanced inversion software (e.g., IPI2WIN)

Applications of VES

Application Field	Case Study Example
Groundwater Exploration	Mapping freshwater/saltwater interfaces in coastal aquifers
Environmental Monitoring	3D contamination modeling in landfills (e.g., Belgium Meerhout case)
Mineral Prospecting	Detecting metallic ores through chargeability analysis
Engineering Geology	Assessing landslide risks via moisture migration patterns

Common VES Equipment

WGMD-4 High-Density Resistivity System

•     Supports 2D/3D/4D modeling with 128 electrodes.

•     Applications: Contaminant plume tracking, aquifer characterization

Case Study

VES Equipment Application Case: Coastal Aquifer Mapping in Kerala, India

Project Background

Challenge: Seawater intrusion threatened Kerala’s coastal areas, requiring precise freshwater-saltwater interface mapping. Traditional drilling (200/meter) failed to provide continuous stratigraphic data.

Equipment Configuration

• Main Device: WGMD-4 High-Density Resistivity System
• Auxiliary Tool: RTK-GPS (±2cm positioning accuracy)
• Software: Res2Dinv inversion system

Implementation Process

1．Pre-survey Design:

• Simulated optimal electrode spacing (AB/2=200m) using Res2Dmod
• Delineated 3 key zones (total coverage 12 km²)

2.Field Data Acquisition:

• Dual-team operation completing 160 stations/day
• Temperature compensation range: 25℃±15℃

3.Data Processing:

• Constructed 6-layer resistivity-depth model
• Validated against 12 boreholes (R²=0.93)

Key Results

Metric	Result	Improvement
Detection Depth	150m	+50% vs conventional VES
Interface Accuracy	±0.5 m	3× better than drilling
Project Cost	$18,000	67% reduction vs full-drilling
Duration	18 days	30% time savings

Scientific Discoveries:

• Identified 2 paleochannel conduits
• Discovered 3 natural saline-resistance geological barriers

Lessons Learned

• Best Practices:

Synchronize tidal data during intertidal zone surveys

CED array outperforms Schlumberger configuration in sandy layers

• Improvements:

Reduce electrode maintenance cycle in high-salinity environments (recommend cleaning every 4 hours)

To learn more about VES, please go to the following link:

Geotech Products| Geotech Instrument Co., Ltd. (geotechcn.net)