Design and Applications of Multi-Frequency Holographic Subsurface Radar: Review and Case Histories

Abstract

Holographic subsurface radar (HSR) is not currently not in widespread usage. This is
 due to an historical perspective in the ground penetrating radar (GPR) community that the high
 attenuation of electromagnetic waves in most media of interest, and the inability to apply timevarying
 gain to the continuous wave (CW) HSR signal precludes sufficient effective penetration
 depth. While it is true that the fundamental physics of HSR, with its use of a CW signal, does not
 allow amplification of later (i.e. deeper) arrivals in lossy media (as is possible with impulse
 subsurface radar — ISR), HSR has distinct advantages. The most important of these is the ability
 to do shallow subsurface imaging with a resolution that is not possible with ISR. In addition, the
 design of an HSR system is simpler than for ISR due to the relatively low-tech transmitting and
 receiving antennae. This paper provides a review of the main principles of HSR through an
 optical analogy and describes possible algorithms for radar hologram reconstruction. We also
 present a review of the history of development of systems and applications for HSR of the
 “RASCAN” type which is possibly the only commercially available holographic subsurface
 radars. Among the subsurface imaging and remote sensing applications considered are
 humanitarian demining, construction inspection, nondestructive testing of dielectric aerospace
 materials, surveys of historic architecture and artworks, paleontology, and security screening.
 Each application is illustrated with relevant data acquired in laboratory and/or field experiments.