Dr. Lin-Ping Song Profile

Dr. Lin-Ping Song

Research Associate at Univ of British Columbia

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Proceedings Article | 29 April 2010 Paper

Transient electromagnetic responses during the transmitter on-time

Gregory Schultz, Jonathan Miller, Lin-Ping Song, Leonard Pasion

Proceedings Volume 7664, 766405 (2010) https://doi.org/10.1117/12.850510

KEYWORDS: Magnetism, Transmitters, Data modeling, Optical spheres, Receivers, Electromagnetism, Electromagnetic coupling, Systems modeling, Sensors, Target detection

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Current time-domain electromagnetic induction instruments generally only utilize data acquired after the cessation of the transmitted field. During this "off time", signals are dominated by induced eddy currents and magnetic surface modes, but do not fully capture the magnetostatic response of permeable and conductive metallic ordnance. In this paper, we investigate the response of EMI systems that measure signals during excitation of the primary magnetic field (the so-called "on-time"). Our analysis shows that on-time signals have great potential to yield useful information that is not often exploited in current EMI systems. We compare analytical models to data from state-of-the-art time-domain EM sensors that have the capability to sample receivers during the on-time. We present modeling results that represent the responses from different current ramps and on-time waveforms for objects and ground. We consider target and clutter objects and grounds having a range of material properties, shapes and sizes, and configurations and investigate signal processing and inversion methods for target detection and discrimination. Specifically, correlations between on-time and off-time signals are shown to be a powerful tool for discriminating ferrous and non-ferrous metallic objects.

Proceedings Article | 5 May 2009 Paper

Transient electromagnetic inversion for multiple targets

Lin-Ping Song, Douglas Oldenburg, Leonard Pasion, Stephen Billings

Proceedings Volume 7303, 73030R (2009) https://doi.org/10.1117/12.818769

KEYWORDS: Polarization, Electromagnetic coupling, Sensors, Data modeling, Electromagnetism, Inverse problems, Magnetism, Transmission electron microscopy, Polarizability, Dipolar polarization

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In UXO contaminated sites, there are often cases in which two or more targets are likely close together and the electromagnetic induction sensors record overlapping signals contributed from each individual target. It is important to develop inversion techniques that have the ability to recover parameters for each object so that effective discrimination can be performed. The multi-object inversion problem is numerically challenging because of the increased number of parameters to be found and because of the additional nonlinearity and non-uniqueness. An inversion algorithm is easily trapped in a local minimum of the objective function that is being minimized. To tackle these problems we exploit the fact that, based on an equivalent magnetic dipole model, the measured electromagnetic induction signals are nonlinear functions of locations and orientations of equivalent dipoles and linear functions of their polarizations. Based on these conditions, we separate model parameters into nonlinear parts (source locations and orientations) and linear parts (source polarizations) and proceed sequentially. We propose a selected multi-start nonlinear procedure to first localize multiple sources and then get the estimated polarization tensor matrix for each item through a subsequent or a nested linear inverse problem. It follows that the orientations of the objects are estimated from the computed tensor matrix. The resultant parameter set is input to a complete nonlinear inversion where all of the dipole parameters are estimated. The overall process can be automated and thus efficiently carried out both in terms of human interaction and numerical computation time. We validate the technique using synthetic and field data.

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