Definitions

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Useful Definitions

Attenuation - The gradual loss of electromagnetic flux through a medium. As frequency waves travel further through a medium, the wave amplitude
will decrease due to attenuation.

Bandwidth - In GPR, this typically means the center frequency that was used.

Conductivity - The ratio of the current density to the electric field. More simply, it is a measure of a material's ability to conduct a current. The more conductive a material is, the more attenuation there will be. An ideal scenario for GPR would be a conductivity reading of zero.

Dielectric - In GPR, a dielectric is any non-conducting subsurface material that contains bound electric charges. In general, almost all subsurface materials                     are considered dielectrics, because almost all materials have some free charge located within them. A material with a high amount of free                             charge is called a lossy dielectric. The higher the amount of free charge, the greater the amount of attenuation.

Dielectric Constant, k - See relative permittivity.

Frequency - The number of waves that occur during a timed interval. All frequency waves travel at the same speed as long as they are traveling through
                    the same material. High frequency waves, however, have more energy and dissipate more quickly than low frequency waves. In GPR, high                         frequency waves are used for detail at shallow depths, and low frequency waves are used when greater depth collection is required.

                      GPR typically uses frequencies between 10 - 1000 MHz.

                                                                                                                    Image Source: Conyers, 471                                                                                                                                                                                                                                                 Image Source: Conyers, 1531

Lossy Dielectric - A dielectric with a large amount of free-charge. Essentially a conductor. Materials like seawater and water-saturated clay are considered                             lossy dielectrics. Due to the high amount of electromagnetic flux flowing through the material, much of the wave's energy is lost as                                     heat; therefore, reflection will be minimal.

Magnetic Permeability - The ratio of a material's magnetic flux density to the strength of the magnetic field. The higher the permeability, the more                                                        attenuation there will be, which will yield a lower quality reflection. The permeability of most materials will have little effect on                                            GPR. Iron-rich soils/sands and some igneous rocks which can contain magnetite, maghemite, and hematite; however, can cause                                               increased attenuation.

Permittivity - The ratio between the material's dipole moment density and the strength of the electromagnetic field.

Radar - A system for detecting objects using both a transmitting and receiving antenna, and a processor unit. Uses radio frequency waves.

Reflection - The ratio of the transmitted wave vs. the received wave. Often described as a percentage.

Relative Permeability - The ratio between a material's magnetic permeability and the magnetic permeability of a vacuum.

Relative Permittivity - Also known as the dielectric constant. A dimensionless measure of how well a material increases capacitance (the ability to store charge energy) compared to air. A low relative permittivity means frequency waves will travel further through the material (less attenuation). More precisely, relative permittivity is the ratio of a material's dielectric constant to the permittivity of a vacuum (epsilon naught = 8.89 x 10^-12 F/m).

Scattering - Occurs when waves are deflected from target surface due to nonconformities in the subsurface. This is often caused by porous materials which                      contain many different relative permittivities, and also by subsurface layers with a wide variety of grain sizes.

Velocity - The speed that frequency waves move through a medium. The speed difference between high and low frequencies should be the same, as long as                  they are traveling through the same medium. Velocity is how the GPR unit determines an estimated depth of objects. The equation used by the                      processing unit is based on the speed of light and the square root of the material's relative permittivity.