Groundwater is an integral part of life and survival. To find, protect and keep our groundwater deposits (aquifers) drinkable, we need to not just drill a hole in the ground, but to gain a deeper understanding of potential threats and opportunities. This is where our non-destructive solutions give you the upper hand.
By pushing electrodes into the ground and injecting a current, the ABEM Terrameter LS 2 can map the subsurface using resistivity. Two electrodes are used to inject a current, and a minimum of two electrodes are used for voltage readings. Knowing the injected current and the measured voltage, the Terrameter LS 2 calculates the resistance of the ground. Depending on the positions of the electrodes, the data will be collected at different depths (Z coordinate) and beneath different surface positions (X and Y coordinates).Learn more
With our ABEM WalkTEM solution, a transmitter loop is laid on the ground, which will be used to generate a magnetic field. A receiver antenna then measures the rate of the magnetic field's diffusion, which is recalculated to resistivity. All data will be collected beneath the same surface position (X and Y coordinates) but at varying depths (Z coordinate).learn more
Everything starts with careful and well documented acquisition of the geophysical raw data. GPS receivers in the ABEM Terrameter LS 2 and the ABEM WalkTEM instruments will automatically store the positions of the instrument along with the raw data, geographically marking where every data set has been collected. Make a note on observations during fieldwork that may have an influence on data quality.
Field data will never be perfect, so in order to prepare and optimize the data for the inversion process, noisy and faulty data has to be removed. Some parts of the data may need to be removed, if it has been have been influenced by
To turn the collected data into a geophysical model, advanced inversion software is used to perform the calculations. The software programs Aarhus SPIA TEM / DC solves the 1D inversion problem for VES and TEM measurements, whereas Aarhus Workbench or Res2DInv solves the inversion problem for 2D resistivity data, and Res3DInv must be used to solve the 3D inversion problem for resistivity.
The inversion process will result in a geophysical model which, in terms of resistivities and depth, gives the best image of the subsurface. The model will always be a more or less good approximation to the real world – hence it is a model – and inconsistencies between the assumed model and the actual earth will exist. It is therefore always important to consider any errors that might have been introduced by choice of the simplified model and also the use of other data sources, either physical or geophysical, to help constrain and improve the model.
The model created by the software is based on parameters of resistivity and depth and must be converted into geological properties and groundwater related information. For this purpose, the relation between resistivity and geological layer properties is essential. The electrical resistivity is an indicative parameter that allows different geological formations to be distinguished from one another.
In groundwater mapping, clay (low resistivity) can be distinguished from sand (high resistivity), or saltwater (low resistivity) from fresh water (high resistivity), or wet sand (lower resistivity) from dry sand (high resistivity).
However, the resistivity to material translation is non-unique and the resistivity interval of the various geological components overlap. Often a certain level of ambiguity may have to be dealt with. Different geological layers in completely different geological scenarios can have the same resistivity, hence some prior knowledge of the geological scenario from geological maps and boreholes should always be a part of a geological interpretation of a geophysical survey.
Examination of the refreshing speed of salinated water in the Netherlands, with the use of Resistivity.
Effective Bolivian groundwater prospecting with ABEM Terrameter LS
Geophysical investigations to ensure the protection of aquifer during re-route of highway.
You need to consider disturbances related to urban areas. VES and ERT are suitable for both urban and rural areas while TEM is not to be undertaken near urban infrastructure, due to the electromagnetic noise and signals induced in utilities, metal infrastructure and objects.
TEM is suitable for all depths, while VES, ERT down to 500 m depth
In case of hard/dry surface, the inductive method TEM is recommended, since it does not require insertion of electrodes into the ground.
Note: Customized plate electrodes or electrodes drilled into the rock is an alternative solution if to still use VES, ERT. Contact Guideline Geo for further information
ERT generates a more detailed picture of the subsurface since the method collects many more data points. Broadly spaced TEM and VES soundings can be a useful method of rapidly assessing the overall structure of large areas. It is also possible to generate 2D profiles from a series of VES or TEM soundings.
ERT – ABEM Terrameter LS 2
VES – ABEM Terrameter SAS 1000, ABEM Terrameter LS 2 VES
TEM – ABEM WalkTEM