The following is a useful collection of geophysical terms. Search through using the alphabetical shortcuts or the “Find” function in your web browser.


A system whereby short electromagnetic waves are transmitted and any energy which is scattered back by reflecting objects is detected. Acronym for radio detection and ranging.


Energy emitted as particles or rays during the decay of an unstable isotope to a stable isotope.


This normally refers to the common, naturally-occurring radioactive elements: potassium (k), uranium (U), and thorium (Th). It can also refer to man-made radioelements, most often cobalt (Co) and caesium (Cs).


Commonly used to refer to gamma ray spectrometry.


A radioactive daughter product of uranium and thorium, radon is a gas which can leak into the atmosphere, adding to the non-geological background of a gamma-ray spectrometric survey.

raw gravity

Also called measured gravity, or observed gravity. The gravity field measured at a gravity station before latitude, free-air, Bouguer or terrain corrections are applied.


The Resource Conservation and Recovery Act, passed by the US Congress in 1976 to regulate solid and hazardous waste disposal.

receiver (Rx)

The signal detector of a geophysical system. This term is most often used in active geophysical systems; systems that transmit some kind of signal. In airborne electromagnetic surveys it is most often a coil. See: transmitter

reduction to equator (RTE)

A mathematical transformation of the total magnetic intensity (TMI) field at its observed inclination (I) and declination (d) to that of the magnetic equator (i.e. I=0°).

reduction to pole (RTP)

A mathematical transformation of the total magnetic intensity (TMI) field at its observed inclination (I) and declination (d) to that of the north magnetic pole (i.e. I=90°, d=0°).

reflection coefficient

A term used in seismic reflection and GPR to describe the ratio of the reflected to incident amplitudes of a pulse reflected from an interface.

regional gravity field

The long wavelength component of the usually attributed to Bouguer gravity field density variations considered to be deeper than general exploration interest; (e.g. the gravity component due to crustal density variations or undulations of the crust/mantle interface). A subjective regional can often be designed to enhance residual anomalies of primary interest.

remanent magnetisation (remanence)

Magnetisation remaining after the application of magnetic field has ceased.

repeat section

A short interval of log that is run a second time to establish repeatability and stability.

residual gravity field

The shorter wavelength component of the attributed to density Bouguer gravity field contrasts within high density basement and/or the lower density overburden. Anomalies in the residual field are usually of exploration interest. A first residual is a difference field obtained by subtracting the regional gravity field from the Bouguer gravity field.

resistivity (ρ)

Electrical resistance to the passage of a current, expressed in ohm-meters; the reciprocal of conductivity.

resistivity depth dransforms

Similar to conductivity depth transforms, but the calculated conductivity has been converted to resistivity.

resistivity logs

Any of a large group of logs that are designed to make quantitative measurements of the specific resistance of a material to the flow of electric current; calibrated in ohm-meters.

resistivity section

An approximate vertical section of the resistivity of the layers in the Earth. The resistivities can be derived from the apparent resistivity, the differential resistivities, resistivity-depth transforms, or inversions.


Refers to the smallest unit of measurement that can be distinguished using a particular instrument or method; based on the ability to separate two measurements which are very close together.

response parameter

Another name for the induction number.


A typical distortion of normal-resistivity logs opposite beds that are thinner than the AM spacing; the effect is an apparent decrease in resistivity in the centre of a resistive unit.


Remedial investigation/feasibility study.