A TOTAL-FIELD MAGNETOMETER SYSTEM FOR LOCATION AND IDENTIFICATION OF COMPACT FERROUS OBJECTS

A self-contained person-portable magnetometer system which accurately locates, identifies, and estimates orientation of compact ferrous obje cts on-line in near real time is described. It consists of a cart-moun ted cesium magnetometer, optical encoder, microcontroller, interface, and laptop computer. The instrument guides the operator to collect sim ultaneous magnetic field and position data in a horizontal plane above an object. Custom algorithms estimate location and dipole moment, whi ch is used to classify the object. Data collection takes 6-13 min, loc ation and moment estimation 5 s, and classification 30 s. Experiments on ferrous spheroids are used to quantify error in estimation of locat ion and dipole moment, error in classification, and relative effects o f error sources. rms error for location vector components was 0.019-0. 045 m compared to the average precision of 0.003-0.005 m. Precision in estimation of the magnitude of the dipole moment was 0.51-8.21% of th e dipole moment, and the accuracy was 24.5 +/- 11.4%. If an experiment al design set were used with the present experimental precision, the m isclassification error should be between 2 and 5%. The misclassificati on rate using a theoretical design set was 28%. For correctly classifi ed objects, angle estimates were generally within 5-10-degrees of the actual values.