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Ground Penetrating Radar (GPR) is one of the most important techniques in near-surface geophysics. The importance of its critical role is best expressed by the wide breadth of its application in all disciplines of near-surface geophysics. In the disciplines such as groundwater hydrogeology, engineering non-destructive testing, contaminant migration monitoring, cultural heritage protection, life search and rescue at hazard sites, national security and counter-terrorism, as well as natural resource exploration, GPR is playing a critical role that is not easily replaceable by other observation techniques. This paper reviews a number of critical aspects in GPR applications in fundamental earth science and applied technologies. Associated with fundamental earth science we review the studies of the internal structure that is critical to the formation of high sand-dunes and desertification. GPR can sensitively respond to the variation of water contents inside a sand dune, and reveal the groundwater condition that critically controls the water supply in desert area. In permafrost detection, GPR is a powerful tool to delineate the interface of the active layer above the permafrost, and is able to image a variety of objects inside the frozen formation such as the ice lens, ice wedge, and boulders. Due to the scattering nature for all these kinds of individual targets, the success of the application of GPR research in permafrost science and engineering should be through broad-band, multi-offset, full three-dimensional data acquisition, analysis, and interpretation. Associated with engineering applications, we review GPR characterization of infrastructure health status in terms of the relativity of the anomaly size and GPR wavelength. We also review the topic of human vital sign detection for rescue, a research area generated much interest in near-surface geophysics community. For completeness of the review we also briefly discuss some techniques evolved based on GPR with the examples in borehole radar, and lunar penetrating radar (LPR). At the end of each section we provide our personal view on the existing problems and bottle-necks of the current status of GPR, and its possible direction for future development.

As geophysicists in general, we also want to remind the readers that even this paper is a review of GPR technique, it is always beneficial to remember that the success of near-surface geophysics, as both a scientific field and technical area, is heavily rely on the collaborative and smart use of multiple types of observation techniques to eliminate the non-uniqueness of geophysical detection as much as possible, to reach the ultimate goal to provide the best possible constraints in subsurface characterization and imaging.