GEOTECH

A Priori information is often used to refer to “knowledge” about the inversion process and geological problem that is not exactly “data”. For example, it may be fair to say that “smooth” models are adequate for modelling the geologic situation. This is A Priori information.

Anomaly is a term that is used in two ways and therefore it is occasionally confusing. In general, the word means anything that is “not normal”. In the context of data, we usually hope that the target or feature of interest will produce a measurable anomaly (variation in the data set) which can then be interpreted in terms of what caused it. In the context of the Earth’s subsurface (or the geophysical model), a feature that can be detected or characterized may be referred to as an anomaly or an anomalous zone.

An electrical physical property which quantifies how well a material allows electricity to flow. It is the inverse of Resistivity.

Forward modelling means calculating a data set that would occur if a survey were gathered over a known model of the Earth. This usage of the word “modelling” is essentially the reverse of the definition above, and this often causes confusion for new users of geophysics.

A geophysical model is a simplified concept of how one physical property is distributed within the Earth. Geophysical models are generally either an object, a halfspace, 1D, 2D, or 3D . Note that a “model of the Earth” can mean either a geological model in which the subsurface is described in terms of rock types, structures, fluids, etc., or a geophysical model defined here.

A discipline of science which uses the tools of mathematics and physics to answer questions about the Earth.

A volume in which half is “air” and the other half is a constant value. Geophysicists consider the earth to be a “halfspace” when the whole volume that is visible has only a constant value of the relevant physical property.

This term is used both to refer to a phenomenon and to the type of field survey that measure this phenomenon. Electric charges in the ground, and the way in which they interact with surfaces of mineral grains, are affected by application of an electric field. The effects can be measured by recording dynamic time or frequency behaviour of potentials caused by the application of the field.

Inversion (or inverse modelling) is the process of mathematically estimating one or more models of subsurface physical property distributions that could explain a data set that was gathered in the field.

An electrical physical property which quantifies how well a material prevents electricity to flow. It is the inverse of Conductivity.

Describes and quantifies the surface of an object or space.  In most cases the term topography is used to describe the surface of the earth but it can also be used to describe or define subsurface structure such as bedrock.

VFR means Visual Flight Rules. It’s a flight in which the pilot must be able to fly the aircraft by looking outside the windows using visual references. Pilot must be able to know where he is and must be able to see other aircraft in the vicinity, avoid them, and also avoid terrain and obstacles.

Versatile Time Domain Electromagnetic system developed and exclusively available at Geotech.

Z-Tipper Axis Electromagnetics