Distributed Radiation Field Estimation and Informative Path Planning for Nuclear Environment Characterization

Abstract

This paper details the system and methods designed to enable the autonomous estimation of distributed nuclear radiation fields within complex and possibly GPS-denied environments. A sensing apparatus consisting of three radially placed Thallium-doped Cesium Iodide (CsI(Tl)) scintillators and Silicon Photomultipliers (SiPm) combined with custom- built pulse counting circuitry is designed and the provided readings are pose-annotated using LiDAR-based localization. Given this capacity, a method that utilizes the radiation intensity readings to first calculate the immediate field gradient and then combine this information to update and co-estimate the believed field intensity and gradient across the whole environment is developed. The strategy propagates the effect of each local measurement through field gradient co-estimation and simultaneously derives a model of the underlying uncertainty. To further support the need for informative data gathering, especially in the framework of emergency and rapid reconnaissance missions, a path planning strategy is also developed that first utilizes the field intensity and uncertainty estimates to select its new waypoint and then performs terrain traversability analysis to derive admissible paths. The complete system is evaluated both in simulation and experimentally. The experimental results refer to the autonomous exploration and field estimation inside an indoor facility within which actual radioactive uranium and thorium ore sources have been distributed.