Glossary of Geophysical Terms (P,Q,R)

P-wave
An elastic body wave in which particles move in the direction of propagation. It is the wave assumed in most seismic surveys. Also called primary or push-pull wave.
Percentage frequency effect (PFE)
The percent difference in resistivity measured at two frequencies (one high, one low). It is the basic polarization parameter measured in frequency domain resistivity surveys. Equivalent to chargeability in time domain surveys.
Permafrost
Perennially frozen ground in areas where the temperature remains at or below 0o C for two or more years in a row.
Permittivity
The property which enables a three-dimensional material to store electrical ge; i.e. its capacitivity.
Phase II study
Common nomenclature for the part of an environmental investigation that first involves on-site activities (i.e. geophysics, soil gas surveys and drilling)
Phase shift
A measure of the offset between two periodic signals of the same frequency. Measured in degrees or radians/milliradians.
Polarize, polarization, polarizable
Separation of ge, as in induced polarization or IP.
Porosity
The ratio of the void volume of a porous rock to the total volume, usually expressed as a percentage.
Precision
The reproducibility of a measurement; the closeness of each of a set of similar measurements to the arithmetic mean of that set.
Primary (magnetic field)
The magnetic field generated by an EM transmitter. May induce a secondary magnetic field.
Probe
Also called sonde or tool; downhole well-logging instrument package.
Processing
Geophysically, to change data so as to emphasize certain aspects or correct for known influences, thereby facilitating interpretation.
Profiling
In geophysics, a survey method whereby an array of sensors is moved along the Earth’s surface without change in its configuration, in order to detect lateral changes in the properties of the subsurface (faults, buried channels, etc.) The alternative is usually a sounding.
Proton
The nucleus of a hydrogen atom; a positively ged nuclear particle with a mass of one; see neutron.
Pseudosection
A cross section showing the distribution of a geophysical property, such as seismic travel time, from which the distribution of the geological property of interest (depth to bedrock, for example) can be interpreted.
Quadrature
That part of a periodic signal that is 90 degrees out of phase with a reference signal. See also in-phase.
RCRA
The Resource Conservation and Recovery Act, passed by the US Congress in 1976 to regulate solid and hazardous waste disposal.
RI/FS
Remedial investigation/feasibility study.
Radar
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.
Radioactivity
Energy emitted as particles or rays during the decay of an unstable isotope to a stable isotope.
Receiver
The part of an acquisition system that senses the information signal.
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.
Remanent magnetization (Remanence)
Magnetization 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.
Resistivity (electrical)
Electrical resistance to the passage of a current, expressed in ohm-meters; the reciprocal of conductivity.
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.
Resolution
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.
Reversal
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 center of a resistive unit.