3-D Discrimination of Buried Object in Subsurface Soil via Magnetic Sensors

The Electrical Conductivity Object Locator (ECOL) has been developed with the goal of detecting buried objects. Its specific capability to detect and characterize small-size plastic and metal objects buffed at shallow depths is demonstrated. The technique can also detect larger objects at greater depths. The ECOL technique maps the soil subsurface conductivity and identifies variations in the conductivity between buried objects and their surroundings. The subsurface conductivity is mapped in two major steps: 1) Low-frequency (1 to 100 Hz) and low-amplitude (<200 ~tA) currents injected into the soil induce potential and magnetic fields in and around the subsurface soil. The potential and magnetic fields are measured using appropriate sensors placed on or above the soil surface. 2) Using the measured values as boundary conditions, a fast optimization algorithm, and an accurate matrix inversion routine, the subsurface conductivity is estimated. Two field tests are conducted using magnetic sensor in either contact or non-contact technique. Both tests successfully located the buffed plastic and metal objects within a radius of 1.2 ft. KEYWORD: Inversion process, Simultaneous Perturbation Stochastic Approximation, Finite Element Method, De-mine