Efficient large-scale underground utility mapping in New York City using a multichannel ground-penetrating imaging radar system

Ground-penetrating imaging radar ("GPiR") combines standard GPR with accurate positioning and advanced signal processing to create three-dimensional (3D) images of the shallow subsurface. These images can reveal soil conditions and buried infrastructure typically down to depths of about 2-3m with high resolution. A commercial GPiR called the CART Imaging System, which was designed for mapping urban infrastructure, has been developed. The CART system uses a radar array consisting of 17 antennas (9 transmitters and 8 receivers) that cover a 2m swath on the ground and can collect data while moving at speeds up to about 1 km/h. A laser theodolite tracks the position of the array during operation. The system collects enough data in a single pass to form a 3D image beneath its track; side-by-side passes are stitched together to create a seamless image of the subsurface. GPiR was first tested on a large scale in a project that mapped an area of approximately 12,000m2 in the south Bronx in four nights. Positions of surface features were also surveyed with the theodolite to provide a local reference grid. Final images were visualized with large-scale maps and electronic movies that scroll through the 3D data volume and show the enormous complexity of the subsurface in large cities.