A geophysical survey is a method of collecting information about the physical properties of rocks and sediments. This method is also increasingly applied to mineral exploration activities. It provides a reliable result of the types of hydrocarbons and minerals present underground without tunneling or digging.
A geophysical survey technique may be classified as either passive or active.
In the passive method, measurements of existing force fields are carried out without instrumentally generated signals, and the results are interpreted in terms of subsurface features.
The active method involves detecting and recording instrumentally generated signals that pass through the subsurface.
There are several different methods and devices used in geophysical surveys, which include:
- Radiometrics – Measurement of the quantities of cesium, thorium, and potassium radiation on the Earth’s surface
- Gravity gradiometry – Measurement of variations in gravitational acceleration on the subsurface
- Magnetometers – Devices used for the calculation of the direction and strength of the magnetic field
- Ground penetrating radar – Investigation of the image of the Earth’s crust using radar pulses
- Magnetotellurics – This method uses electromagnetic instruments for mapping the Earth’s surface, based on the differences in magnetic and electric fields
- Seismic tomography – It provides a three-dimensional map of an area by resisting ground vibration waves
Most of the geophysical survey methods involve the formation of a grid with respect to the Earth’s surface. A baseline is established near the longest edge of the survey area and marked with ranging poles. A second baseline is established perpendicular to the first baseline.
This method is applicable for squares of any size, where each square is divided into numerous squares containing a reading.