Real-Time Handheld Magnetometer Array
The objective of this project was to build, test, and characterize a diver-held ferrous metal detector array with real-time processing algorithms that accurately determines the position, depth, and size of magnetic anomalies from unexploded ordnance (UXO). This was accomplished by using an array of prototype low-power, miniature, total field atomic magnetometers, designed using new miniaturized electronics and a novel digital approach. Specific technical objectives were as follows:
- Design and build an optimal array of total field sensors,
- Design and implement real-time anomaly detection and analysis, yielding location, depth, and size of detected anomalies,
- Test, characterize, and optimize the performance of the system,
Design digital electronics to drive the sensors.
Total field atomic magnetometer sensors are often used in making detailed surveys of underwater sites containing UXO. Such sensors are deployed on large wings or tow bodies. After the data are gathered, scientists typically plot and analyze them, then populate lists of targets requiring remediation. Finally, divers return to relocate these targets and the objects are removed. We previously developed atomic magnetometer sensors whose power consumption is an order of magnitude lower than previous magnitometers. This enabled the design of small systems containing two-dimensional sensor arrays that have the desirable sensitivity and noise immunity properties of existing magnetometer devices.
Many significant results were achieved during this project. First, the team determined an optimal number and positioning of sensors to be used to effectively analyze dipole targets in real time, using a reasonably sized array. Secondly, the team developed a real-time inversion algorithm and user display interface allowing us to test the system. Thirdly, the team built a prototype array of 12 sensors to test the performance of the system. Running the inversion algorithm in real-time worked as well as hoped, and actually yielded unexpected benefits in analyzing complex situations. Finally, in order to realize a portable system, the team designed and built a miniature electronics system, using an all-digital approach to the signal extraction, which yields small size and low power consumption.
With such an array of sensors, now there is the ability to run processing algorithms in real-time. This is made possible by gathering data suitable for dipole source analysis in a single instant. By analyzing the data on the spot, an instrument could guide a diver toward the target, while indicating the depth, size, and magnetic properties of the anomaly as well. Having such an instrument will allow the operator to better judge whether he or she has actually acquired the desired object, by comparing the object’s size, depth, and signature with that obtained on the initial detailed survey. In addition, the diver may scan nearby to determine if other objects are present. Furthermore, after exposing the object under investigation, another scan may be performed to determine if additional UXO might have been misidentified as a single anomaly in the initial survey. Such an instrument could even eliminate the need for an initial detailed survey.