LARGE-SCALE MAPPING OF COMPLEX UTILITY LINES WITH A BROADBAND ELECTROMAGNETIC INDUCTION ARRAY

A prototype broadband (60 Hz to 100 kHz) electromagnetic (EM) induction array is used to map complex utility lines. The trailer-based array utilizes 16 vector broadband electromagnetic induction sensors configured in 2 rows of eight sensors with a vertical offset of 0.6 m. The array is monitored by an accurate positioning system (cm accuracy) and moves freely, collecting EM data in arbitrary patterns on a 30 cm grid. The data from adjacent passes (2 m wide) are merged together to provide seamless coverage. Proprietary software using advanced signal processing in combination with iterative numerical forward and inverse modeling methods is used to determine utility lines location and depth. Multiple “clamp-on” sources directly couple to a particular utility line of interest. Each source operates at a different frequency. Typical frequencies used are in the range of 8 kHz - 83 kHz. Additionally, lines are mapped using ambient 60 Hz signal from power transmission lines. The array of broadband vector electromagnetic induction sensors collects data as a time series. Detailed maps are created from the three orthogonal electromagnetic field polarizations. Two case histories are presented demonstrating the systems capability to help untangle complex utility networks.