Semiautomated georadar data acquisition in three dimensions

Abstract

Under favorable conditions, georadar techniques can provide vivid images of the shallow subsurface (<10–50 m). Although the significant advantages of 3-D georadar surveying strategies are well documented, they generally require much greater expenditures than traditional 2-D approaches. We introduce an efficient, semiautomated 3-D georadar acquisition and processing scheme that does not jeopardize data quality. A standard georadar acquisition unit is integrated with an innovative self‐tracking laser theodolite with automatic target recognition capabilities. Georadar and coordinate data are recorded simultaneously as the georadar antennae are transported steadily across a survey area. While tracking a target prism mounted between the antennae, the theodolite provides real‐time coordinate information with high accuracy in all directions. At ∼1 m/s (moderate walking speed) the coordinates are determined to better than ±0.04 m, and at ∼3 m/s they are better than ±0.07 m. Subsequent to acquisition, semiautomatic processing allows the georadar data to be static corrected, transferred to a regular grid using a novel 2-D Fourier transform method, amplitude modulated, filtered, and displayed. The acquisition component of the new scheme is five to ten times faster than standard step‐mode georadar techniques, and the semiautomatic processing component allows initial 3-D images to be viewed in the field. Typically, a 3-D georadar data set covering a 25 m × 25 m area may be collected and processed in less than 3 hours. One such data set recorded across a former glaciofluvial environment allows reflections from complex river channel sediments and surface features to be readily identified and interpreted.