“True” 3D Acquisition using GPR Over Small Areas: A Cost Effective Solution

GPR 3D Investigations ensure the correct and proper reconstruction of an object within a surveyed space, and the final image is effectiveand understandable by the end-user. using GPR, a new positioning system called PSG (Pad System for Georadar) was developed for “true” 3D acquisitions over small areas. the system allows the easy and fast acquisition of a geo-referred, regular and dense matrix of GPR traces that satisfies the Nyquist theory for both in-line and cross-line directions. Two prototype GPR systems were assembled by combining the PSG with a dual-polarization antenna (HH and VV). One prototype was equipped with a bipolar high frequency 2GHz antenna and was tested on a concrete slab to map the rebar and determine how the marble slabs covering the investigated structure were anchored. the results were excellent, and a “true“ 3D GPR survey of a 100cm*100cm area was made in about 20 minutes, surveying both the vertical and plane surfaces in situ. This prototype acquired the minimum number of GPR traces at regular intervals in both in-line and cross-line directions, thus satisfying the Nyquist theory. Furthermore, all the traces had the same polarization as the grooved tracks of the PSG ensure that the GPR antenna always faces the same direction at every point of the investigated area. the second prototype had two 200MHz antennas assembled perpendicularly to simulate the HH and VV antenna dual-polarization. Also this prototype resulted in the profile acquisitions being taken in only one direction, and the result was a regular, and sufficiently dense, data grid that made it possible to acquire 3D images of linear objects independently of their direction. to assess the utility of the PSG system it was tested on 16 small urban sites (3m*3m); the GPR results of these tests were then compared with observations made during maintenance operations that involved the digging up of all the pipes at the sites. the reconstruction was found to be correct in all directions.