Abstract
Holographic subsurface radar (HSR) is not currently in widespread usage. This is due to a 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 time-varying gain to the continuous-wave (CW) HSR signal preclude 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 of the RASCAN type, which is possibly the only commercially available holographic subsurface radar. 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.
Highlights
The earliest (1960s/1980s) subsurface radars were developed for electromagnetic detection of objects up to several meters below the ground surface [1,2,3]
Holographic subsurface radar (HSR) is analoto the to optical hologram technology first achieved by Gaborby in 1948
The items were buried horizontally clearly in HSR, but only the upper one shows on metal detectors (MDs) because the metal arming pin has in a sand test bed and scanned with at a frequency of 3.8 GHz
Summary
The earliest (1960s/1980s) subsurface radars were developed for electromagnetic detection of objects up to several meters below the ground surface [1,2,3] This was dictated by the achievable (at that time) operational frequency range of 100 MHz to 500 MHz for impulse radar. Depth resolution in this band was limited to 0.5 m to 1 m in the common media of soils and freshwater ice [3]. These early applications coined the widely used name ground-penetrating radar, or the abbreviation GPR.
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