Geoelectrical surveys with static and dynamic – onshore and offshore Electrical Resistivity Tomography (ERT) and Vertical Electric Sounding (VES) methods
Direct current electrical methods belong to geoelectrical measurements to map the electrical properties of the subsurface. The rocks and different geological units cover several orders of magnitude of specific resistivity and these rocks usually can be described by an approximate resistivity. These differences allow us to identify and localize anthropogenic and geological features. However, similar object might not belong to the same unit, geophysical and geological expertise provide solution for just interpretation.
Or company owns a Hungarian DIAPÍR-18 and DIAPÍR-10R VES instruments and a 10 channel Syscal Pro Switch 96 (manufactured by Iris Instruments) ERT system.
We use our VES tools for large-scale geological mapping, to evaluate strata in a larger area of interest. We utilize this method for geological investigation for evaluations of water resources protection and water resource vulnerability.
Our ERT system has a great variety of accessories: we not only carry out traditional static ERT measurements but dynamic measurements (our unit is towed by a pick-up) and offshore surveys as well. We measure usually shallow objects up to 100 m: cavity research, polluting source localization, geological support for geotechnical planning, identifying and localizing water supplies (e.g.: gravel zones).
Electromagnetic surveys with Very Low Frequency (VLF), Radiomagnetotelluric (RMT) and Slingram methods
GeoGold Kárpátia Ltd has always emphasised the mobile, cost-efficient electromagnetic methods.
During Very Low Frequency (VLF) and Radiomagnetotelluric (RMT) measurements we utilize very distant military or navigational broadcasts to gain information of the EM properties of the subsurface. These EM waves penetrate the ground where eddy currents are induced in conductive zones. As a result, a secondary magnetic field is induced, and we detect the superposition of these primary (broadcast) and secondary magnetic field. Traditional VLF instruments operate at 10 to 30 kHz and RMT operates 10 to 240 kHz, sometimes up to 300 kHz.
We own a combined VLF-RMT instrument, developed by the Centre for Hydrogeology and Geothermics, University of Neuchatel, which can operate in VLF-EM, VLF-RMT and VLF-EM-GRAD modes.
Our specialty is the Slingram-400 that we adapted and improved, which is an active frequency-domain EM system (110 Hz – 7,040 kHz). During measurements with our system, we can costumize the transmitter-receiver distance, so we are able to fit our settings as close to the task as it possible.
These methods can relatively fast and cost-efficiently detect conductive zones in the subsurface such as fracture-systems, karstic and fractured rocks, dykes and public utility.
Geomagnetic surveys with Cesium-vapor and Proton-precession magnetometer.
Mapping the subsurface with magnetic methods is a solid method of near-surface geophysics. During magnetic surveys we detect the changes in the magnetic induction due to the different magnetic susceptibility of the different materials in the subsurface. We utilize magnetic measurements for geological mapping, archaeology, utility mapping, UXO localization.
Our company owns a G-858GAP cesium-vapor magnetometer (with gradient setup), manufactured by Geometrics Ltd (USA). It is a high-precision – high-resolution magnetometer connected to a Tallysman GPS that allows cm precision localization during surveying.
A G-857 type proton-precession magnetometer by Geometrics Ltd is also at our disposal that we use for base station for diurnal correction to filter daily variations of the Earth’s magnetic field during our surveys.
Reflection and Refraction Seismic surveys
During reflection and refraction seismic methods we observe the acoustic wave propagation properties of the subsurface with a suitably chosen signal generator with geophones. The method is based on the wave travel time between the source and the detectors. With refraction seismic method, we can define the layers with different elastic properties and their speed in a geological setting when the characteristic wave velocities of the rocks are increasing with depth. These interpreted primary and secondary velocity maps provide a reliable and cost-efficient information about the subsurface. The characteristic propagation velocities depend not only on the material but on the compactness as well. This type of seismic surveying for geology with geotechnical consideration bear high importance in many fields: cavity research, civil engineering, investigation of buried structures. Reflection seismic is a useful tool in mapping geological structures, identifying layer boundaries with higher resolution for mostly stratigraphic mapping. An advantage of the refraction seismic method over the reflection method its higher accuracy in depth-time conversion.
Our company owns a German SUMMIT X ONE system by DMT. This is a system with one cable connecting the PC and the geophones making it highly mobile and versatile.
Ground Penetrating Radar with 100, 500 and 800 MHz antenna
Ground Penetrating Radar (GPR) is a highly useful tool for mapping the upper soil. It beams high frequency EM waves to detect the signals coming back from layer boundaries and changes in soil qualities. The EM wave propagation depends on the dielectric constant, magnetic permeability and the specific conductivity of the materials.
This method is useful for aercheological and geotechnical surveying, mapping of utilities, evaluation of dam structures, localization of metal objects (e.g.: steel rods in reinforced concrete, munition) depenging on the applied frequency in a fully non-invasive way.
Our company owns a Swedish MALA ProEx GPR unit with 100, 500 and 800 MHz shielded antennas. We carry out measurements from 10 cm of depth of investigation up to several meters, mostly combining different frequencies for 2D and 3D surveying.