Introduction and History Electromagnetic Wave Propagation
Velocity Wavelength Attenuation Dispersion
Rocks, Soils and Fluids: Electrical Properties Magnetic Properties
Environmental Influences Heterogeneity, Anisotropy and Scale Radar Equation
Scattering Polarization Fresnel Reflection Snell Angle Stokes-Mueller Matrices Poincare Sphere
Near Field and Far Field
![[Under Construction]](images/undercon.gif){kind=small}
Most discussion and usage of ground penetrating
radar assumes wave propagation in the far field. The far field is defined in several
different ways, but generally means far enough from the antenna to be approximated as a
plane wave, and 'far enough' usually means more than a wavelength away. Exactly how
far away the transition from near field to far field occurs is a function of the
wavelength, the geometry and size of the antenna, and the electromagnetic properties of
the ground. In the immediate vicinity of the antenna, called the 'near field', the
behavior of wave propagation is different than it is in the 'far field'. Some radar
systems filter the data and remove the near field effects. However, under certain
circumstances, the ground penetrating radar response in the near field can be very
useful. The near field response has been used to detect incipient dessication cracks
in clays (such as threaten the space shuttle landing strip at Edwards Air Force Base),
locate land mines, map density changes in soil compaction studies, and more.
The far field is dominated by homogeneous waves and the near
field is dominated by inhomogeneous (or evanescent) waves...
(references)
(illustration)
Waveguides Multipathing Resonance
Survey Design Contrast Geometry Resolution Depth of Investigation Orientation
Data Acquisition Data Processing Modeling Interpretation Uncertainty
Applications: Noninvasive Surface Borehole Airborne Satellite and Space