A meaningful 3-D data presentation requires a high geometric fidelity in the collection of the GPR data. Since Synthetic Aperture Focusing Techniques require several samples per space time wavelength, an enormous amount of data must be collected, which precludes manual movement of the antenna. To permit this new GPR concept, a computer controlled scanner has been built. It consists of a 5 m long linear movement unit with a ball screw connected to a servo motor. A second servo motor is connected to pairs of small wheels used to move the linear unit in the transverse direction. The stroke of the linear unit is 4.5 m and within that length the antenna can be positioned at submillimeter accuracy. At full speed the antenna travels over the linear unit in 12 s. The maximum vertical deflection with a 5 kg load is 1 mm. The weight of the scanner is approx. 75 kg with no load. After a period of evaluation of various concepts, a second scanner will be built to facilitate bistatic measurements. That way the 2-dimensional back scatter field can be determined, generating data suitable for processing in 3-D seismic packages. Using the previously developed 5 channel GPR controller, MRS, and 2 orthogonally polarized antennas on each scanner, it is possible to obtain the polarization matrix. Since MRS allows each connected antenna to work either as a transmitter, a receiver or both it is possible to measure the back scattered field around one point of transmission although the scanners can not cross. Since the computer that acquires all the data and displays it is the same that controls the scanner, it is also possible to draw marks on the ground with a spray can connected to the scanner. To visualize the great quantity of 3-D data, acquired with this scanner, the help of 3-D display and interpretation software was found indispensable. Such software is commonly used in the field of oil exploration to interpret three-dimensional subsurface structures. Before interpretation, the 3-D data cube was prepared for visualisation with several seismic data processing routines including filtering, deconvolution/envelope and migration. Depending on the data quality , "a priory" knowledge, and complexity of the subsurface structure the processed data was found to display a clearer image than the raw data. Several visualization techniques as time slices (windows), cube-, chair-display and flying carpet were compared and evaluated towards their usefulness in enhancing the subsurface image. An animation of the 3-D data was found indispensable for the interpretation of the data and is presented here.


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