Geophysical survey is the systematic collection of geophysical data for spatial studies. Detection and analysis of the geophysical signals forms the core of Geophysical signal processing. The magnetic and gravitational fields emanating from the Earth’s interior hold essential information concerning seismic activities and the internal structure. Hence, detection and analysis of the electric and Magnetic fields is very crucial. As the Electromagnetic and gravitational waves are multi-dimensional signals, all the 1-D transformation techniques can be extended for the analysis of these signals as well. Hence this article also discusses multi-dimensional signal processing techniques.
Geophysical surveys may use a great variety of sensing instruments, and data may be collected from above or below the Earth’s surface or from aerial, orbital, or marine platforms. Geophysical surveys have many applications in geology, archaeology, mineral and energy exploration, oceanography, and engineering. Geophysical surveys are used in industry as well as for academic research.
The sensing instruments such as gravimeter, gravitational wave sensor and magnetometers detect fluctuations in the gravitational and magnetic field. The data collected from a geophysical survey is analysed to draw meaningful conclusions out of that. Analysing the spectral density and the time-frequency localisation of any signal is important in applications such as oil exploration and seismography.
Types of geophysical survey
There are many methods and types of instruments used in geophysical surveys. Technologies used for geophysical surveys include:
- 1) Seismic methods, such as reflection seismology, seismic refraction, and seismic tomography.
- 2) Seismoelectrical method
- 3) Geodesyand gravity techniques, including gravimetry and gravity gradiometry.
- 4) Magnetic techniques, including aeromagnetic surveysand magnetometers.
- 5) Electrical techniques, including electrical resistivity tomography, induced polarization, spontaneous potential and marine control source electromagnetic (mCSEM) or EM seabed logging.
- 6) Electromagnetic methods, such as magnetotellurics, ground penetrating radar and transient/time-domain electromagnetics, magnetic resonance sounding (MRS).
- 7) Borehole geophysics, also called well logging.
- 8) Remote sensing techniques, including hyperspectral.