Evaluation of Target Picking Methods for Magnetic Data

Abstract : Due to the large numbers (up to tens of thousands) of possible targets identified in nominal UXO surveys, efficient and reliable machine-aided target pickers should be used to identify targets for subsequent characterization. When selecting anomalies, the goal is to identify all anomalous features that may be caused by UXO while minimizing operator time and eliminating operator bias. To facilitate advanced physics-based modeling, however, the target pickers should also be able to select data appropriate to the target, i.e., to outline or estimate the anomalies spatial extent. The current approach to target selection is either manual identification or amplitude thresholding. The former is time intensive, not clearly defined, and prone to operator bias. The latter is sensitive to noise and is prone to over- or under-picking unless judicious oversight is exercised. Neither approach provides measures for estimating the footprint of the anomaly. The impact to the DoD is obvious. Systematic, fast, and robust target pickers can save money and produce a defensible target list compared to the current methods. This project evaluated four automatic target pickers against the manual method and transitioned them to the user community via Oasis montaj(TM) by building custom Geosoft Executables(GX). Oasis montaj(TM) is a geophysical data processing and visualization package developed and marketed by Geosoft Incorporated. The four automatic target pickers were: (1)a wavelet-based detection algorithm, (2)clustering positive and negative peaks, (3)a dipole-based matched filter, and (4)analytic signal. The demonstration was broken up into two phases. The first phase used a 60 dipole synthetic data set to explore the parameter space and optimize the algorithms for the four automatic target pickers. The result of phase 1 was a set of starting parameters that was used in phase 2. The second phase applied the target pickers to 7 magnetic data sets using the parameters output from phase 1.