Multiple Source Localization by Sensor Fusion of Digital Magnetic Compass Data with Spectroscopic Data

Abstract

A technique is shown to estimate the location of a source with a single detector. The method exploits an angular histogram of counts calculated by the fusion of the digital compass data with spectroscopic quantities like the count rate. The perimeter around the user is divided into N discrete segments. Storing the count rate in dependency of the angle towards north allows to calculate a count rate per segment, thus indicating from which direction the radiation comes from. This approach builds upon former works conducted with a gyroscope, showing that the compass is a more robust tool for the localisation. Additionally, it extends the perspective from finding a single source to the localisation of multiple sources. Considering the application to a handheld radioisotope identification device, different hand motions are investigated and compared, where waving apparently has the best angular detection rates. The method also uses a graphical visualisation to guide the user towards the source. This tool is a compass rose combined with a segmented display of the angular count distribution. A single source and two sources are resolved by technique and graphical examples of the visualisation interface are presented. Also the aspect of moving towards or away from a source is covered. Here, segments to the front and segments to the rear are filled, based on the response of an additional gyroscope. Test setup and test results are described. Crucial for resolving the position of a source is the ratio between motion radius and distance to the source. Distant sources do not vary enough to be resolved by waving motions. In such cases, full circle rotations are recommended, using the body of the user a temporary shield to increase the performance of position determination.