The Combined Use Of Magnetic And Electromagnetic Sensors For Detection And Characterization Of Uxo

Data has been collected on a test field of inert UXO with both a Geometries 822A total field<br>magnetometer and a Geonics EM61 pulsed, electromagnetic induction sensor. This study<br>allows comparison of the two instrument’s detection capabilities. While the EM61 as<br>currently configured is not as sensitive as the 822A in terms of depth of detection, it does<br>detect objects of interest down to IO-l.5 feet, as well as detecting non-ferrous materials.<br>While the location, depth, and size of single UXO targets are readily estimated from<br>magnetic measurements, it is not as clear what can be done with an electromagnetic sensor<br>that will synergistically add to the capability of the magnetic sensor. Based on laboratory<br>measurements, electromagnetic sensors may be capable of size estimation based on their<br>temporal response. For frequency domain instruments such as the EM31, this involves<br>measuring the phase angle response. For time domain instruments such as the EM61, this<br>mvolves recording the time decaying response. This size estimation is not affected by<br>remnant magnetization and also reflects the size of individual objects in a collection of<br>obiects. Because the spatial response of an electromagnetic sensor involves the relative<br>geometry of the transmitter, the object, and the receiver, it is expected to be sensitive to<br>obiect orientation. Measurements made on large elongated UXO in different orientations<br>confirm this.