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


half-life

Radioactively, half-life is the time required for half of a given quantity of material to decay. Chemically, it is the time required for half of a given quantity of material to undergo a chemical reaction.

halfspace

A mathematical model used to describe the Earth as infinite in width, length, and depth below the surface. The most common halfspace models are homogeneous and layered earth.

HEM
Helicopter ElectroMagnetic. This designation is most commonly used for helicopter-borne, frequency-domain electromagnetic systems. The transmitter and receivers are normally mounted in a bird or on a loop carried on a sling line beneath the helicopter.
herringbone pattern

A pattern created in geophysical data by an asymmetric system, where the anomaly may be extended to either side of the source, in the direction of flight. Appears like fish bones, or like the teeth of a comb, extending either side of centre, each tooth an alternate flight line.

HFEM
Helicopter Frequency-domain ElectroMagnetic, This designation is used for helicopter-borne, frequency-domain electromagnetic systems. Formerly most often called HEM.
high density basement

The deepest significantly thick, high density unit(s) within the geologic section of an area, which provide a major positive density contrast. The rocks above the major density contrast are usually younger sediments and/or volcanics, typically having densities ranging from approximately 1.9 g/cm3 to 2.6 g/cm3. Those below the major density contrast are usually older sedimentary, volcanic and/or crystalline rocks, typically having densities ranging from 2.6 g/cm3 to 3.0 g/cm3. High density basement may or may not be equivalent to crystalline and/or magnetic basement.

high resolution aeromagnetics

This might more correctly be termed “high precision aeromagnetics”. The term has gained wide acceptance in the industry to denote surveys flown at low terrain clearance (30-150 m), with close line spacings (25-500 m), recorded at high sample rates (0.1-0.25 s), and acquired with high-sensitivity magnetometers (0.001-0.005 nT).

homogeneous

This is a geological unit that has the same physical parameters throughout its volume. The response may change with system direction (see anisotropy).

HTEM

Helicopter Time-domain ElectroMagnetic, This designation is used for the new generation of helicopter-borne, time-domain electromagnetic systems.