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
Antennas Coupling Near / Far Fields Waveguides Multipathing Resonance
Survey Design Contrast Geometry
Resolution
![[Under Construction]](images/undercon.gif){kind=small}
Resolution is controlled by the wavelength
and polarization of the electromagnetic energy, the contrast in electromagnetic properties, and the size, shape, and
orientation (geometry) of the target, and may be a function of noise in practice. Resolution increases with increasing
frequency (decreasing wavelength), but at the expense of depth
of investigation (which generally improves with decreasing frequency).
Unlike lower frequency electromagnetic induction methods, ground penetrating radar
resolution is not logarithmic with depth. In a few dry materials, resolution is
nearly constant with depth. In most materials however, resolution decreases with
increasing depth as frequency dependent properties cause pulse
broadening. This is an effective increase in wavelength with depth from low pass
filtering the frequency content of the signal.
Roughly equidimensional objects, such as cubes or spheres, that are 1/3
of a wavelength in cross-sectional size in typical noise environments (or about 1/10 of a
wavelength in exceptionally quiet environments) are resolvable if they have sufficient
contrast in properties compared to the background. Objects that are elongated in one
dimension, such as rebar, pipe or wire, must have the orientation of the long dimension
aligned with the polarization of the electric field for optimal detection. For
objects which are surfaces, such as stratigraphic layering or water tables, resolution is
a function of geometric and angular
alignments, layer thickness (greater than 1/10 wavelength), and surface
roughness. Further, the rate of spatial change in properties between the target
and the host medium are important: if the change is a sharp contrast (like a water table
in coarse grained soils), the resolution is higher than if the change is gradational (like
a water table in fine grained soils with a thick capillary fringe). In addition,
there may be special geometric situations in which waveguides
or constructive and destructive interference (multipathing) may
be important.
Depth of Investigation Orientation
Data Acquisition Data Processing Modeling Interpretation Uncertainty
Applications: Noninvasive Surface Borehole Airborne Satellite and Space