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Multi-Channel GPR System
THE TERRAVISION™ SYSTEM
UIT's proprietary multi-channel GPR system includes a 14-channel, cart-based ground penetrating radar unit that is typically towed behind a vehicle during survey operations. The GPR Terravision™ system consists of two banks of seven (7) antennas each with a fixed spacing of 0.4 ft (12 cm) between each antenna module. Data acquired by each of the 14 channels is spaced at 0.08 ft (2.5 cm) in the direction of travel. The central frequency and approximate bandwidth of each GPR antenna element is 400 MHz, a combination that provides both good penetration and high resolution. The 14-channel system is capable of imaging a 5.12 ft wide data swath in a single pass. Multiple survey passes are typically performed to create a three-dimensional (3-D) data set covering the entire project area. Unlike other multi-channel systems and most single GPR units, the Terravision™ system has the ability to accurately position data along arbitrary curvi-linear traverses and it generates a GPR data set that is sampled in a spatially uniform manner in all directions along the surveyed surface.
The Terravision™ system plays a critical role in quickly and efficiently completing 3D mapping of the subsurface. The system acquires data at speeds of up to 5 miles per hour across the ground surface with acquisition timing controlled by a wheel encoder. Positioning information is logged via the Data Acquisition Shell (DAS) software application with either a real-time kinematic global positioning system (RTK-GPS) or laser-theodolite positioning system. Data recorded via each multi-sensor antenna bank is stored in separate computers housed within the GPR control unit, then downloaded to the primary acquisition computer. During the download process, data sets from the 14-channel GPR are sorted and tagged with the appropriate GPS survey (surface position) information.
Following acquisition, data is processed using standard GPR algorithms and then merged with appropriate positioning data files. Multiple survey swaths, geo-referenced to the desired coordinate system, are assembled into a composite 3-D data block of the project area using the DPE data software application and subsequently loaded into SPADE. The unique GPR data viewer within SPADE enables buried utilities and other subsurface features to be correctly and efficiently interpreted. SPADE has unique capabilities that enable easy detection and identification of targets. For example, one can sequentially view area presentations of 3D data blocks from surface to maximum sampled depth, or generate cross-sectional slices at any user-specified angle. The operator of the Terravision™ system selects and records detected target locations, depths, and orientations using tools that allow the information to be properly and accurately documented and/or transferred to standard CAD/GIS software for mapping and presentation. UIT's Terravision™ mapping services permit the accurate determination of the location of many different types of underground objects.
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