Technology > Subsurface Imaging Tools > Multi-Sensor TDEM System
ElectroMagnetic Induction (EMI), or more specifically, Time Domain ElectroMagnetic induction (TDEM), is a geophysical method for detecting both ferrous and nonferrous materials below ground. TDEM locates features like metal pipes and changes in rock and soil conductivity caused by drilling, trenching and other construction operations.
UIT uses an array of three individual multi-sensor TDEM units, each having four data channels. The units are placed on a custom-made cart that may be towed behind a vehicle such as an ATV, golf cart, or light truck. Both the multi-sensor TDEM and the multi-channel GPR arrays are often used together and are towed at the same time. Unlike some EMI systems, UIT’s TDEM requires no physical connection to buried utilities and provides extremely accurate details of underground features.
The UIT multi-sensor TDEM system is configured and synchronized to operate simultaneously as a single array along a survey swath. The TDEM coils are mounted on an electrically non-conductive deployment cart. The complete system is able to cover a five-foot wide swath in a single pass at survey speeds of up to 5 miles per hour. It is not necessary to establish a survey grid prior to data collection, which is typically required during standard EMI surveys. The TDEM array is calibrated in an area free of conductive objects prior to surveying in order to maximize the response to any buried metallic features such as pipes, tanks or cables.
Information acquired from the four data channels in each of the three TDEM systems is time-stamped together with position information obtained simultaneously by the cart-mounted GPS.
Subsequent use of the Data Processing Engine (DPE) software converts the GPS data to the desired coordinate system and merges it with the TDEM data. Plan-view contour plots of the TDEM data are ported into SPADE where data is overlaid onto aerial photographs or maps of the project area. Coordinates of subsurface targets and other features of interest are selected in SPADE and exported to project CAD/GIS maps. The depth to buried targets is computed using proprietary target inversion algorithms placed in SPADE.
The above described multiple sensor TDEM technology package, hardware and software, is unique to UIT.