Coherent laser ranging of deforming objects in fires at sub-millimeter precision

Light Detection and Ranging (LiDAR) is a powerful tool to characterize and track the surface geometry of solid objects. In a fire, however, no method has excelled at measuring three-dimensional shapes at millimeter precision while offering some immunity to the effects of flames. This paper applies coherent Frequency Modulated Continuous Wave Light Detection and Ranging to capture three-dimensional measurements of objects in fire at meters of stand-off distance. We demonstrate that despite the presence of natural gas flame depths up to 1.5 m obscuring the target, measurements with millimeter precision can be obtained. This is a significant improvement over previous work making the technique useful for many fire research applications. An approach to achieve sub-millimeter precision using spatial and temporal averaging during post-processing is presented. The technology is demonstrated in case studies of structural connection and vegetation response in fires. •Coherent laser ranging to capture three-dimensional point clouds of objects in fires.•Position uncertainty due to beam steering caused by flames is characterized.•A method to increase position precision while ranging through fire is implemented.•Case studies for structural connection and vegetation response to fire are provided.