Subsurface Pipe Detection with an Array of Inductive Broadband Vector Receivers

An electromagnetic induction survey was conducted using an array of inductive receivers (AIR) to map and verify a network of water lines in a western city in the USA. Data was collected on a 30 cm by 30 cm grid covering 2800 m2. The array utilizes 16 vector broadband electromagnetic sensors arranged in two rows of eight sensor pods. The position of the system was measured using a robotic laser tracking system which records position information with sub-centimeter accuracy. Multiple active “clamp-on” transmitters were used to induce signals into the water lines and other nearby utilities. Each transmitter operated at an individual frequency in the range of 1 kHz – 83 kHz. In addition, ambient signals, such as electric power transmission frequencies were measured. Detailed magnetic field maps are created for each particular frequency of interests and for any combination of the three magnetic field polarizations. Qualitative positions and depth of current carrying lines can be done by directly assessing the magnetic field maps. Magnetic field inversion methods were used to quantitatively determine positions and depths of current carrying lines.