A Comparison of Metrology Used in Documenting Shooting Incident Trajectories
Toby Terpstra, Alireza Hashemian, Tilo Voitel, & Jonathyn Priest
Abstract: There are several methods and tools for documenting trajectory rods, but little research exists comparing accuracies of these methods. In this study, three targets were constructed, each having two sheets of ¼ in (.635 cm) plywood separated by a 3½ in (8.89 cm) void. Three shots from varying locations were taken at each of the targets for a total of nine shots. Prior to each shot, muzzle locations were documented with a total station, and afterwards the bullet hole locations were documented with the total station as well as a 3D laser scanner. Trajectory rods were then inserted through the primary and secondary bullet holes in the plywood targets and aligned using centering cones. This study compares the resulting accuracies from six different methods for documenting the trajectory rods. For each method, the resulting horizontal and vertical trajectory angles were compared to the baseline LiDAR mapping of the bullet holes and muzzle locations. A total of 102 measurements were taken with a combined average horizontal angle accuracy of 1.2° and a standard deviation of 0.9°. The average vertical angle accuracy was 0.7° with a standard deviation of 0.5°.
Estimating Occult Timing of Surprise Gunshot Sounds in Silent Film via Observed Start of Human Voluntary Reactions of Concern
Brian Roselle & Kenneth Scearce
Abstract: Voluntary human reactions, and associated perception times when reaction movements commence, are identified to estimate gunshot sound arrival time to subjects in a shooting scenario recorded on silent film. Common involuntary reactions (startle) and voluntary reactions are reviewed to help identify proper reaction types being observed and apply in back-calculating gunshot timing. With a focus on voluntary reactions, values for perception time as a function of stimulus expectancy, specifically in the case of a surprise stimulus, are determined by reapplication of brake perception-reaction time (brake PRT) modeling of extensive driver reaction time studies in traffic flow theory. Using a modified model in conjunction with sampling human reactions observed on film allows back-calculating surprise gunshot sound timing. To detail use of this approach, a well-known example of a silent film, the Abraham Zapruder film of the Kennedy shooting, is considered to help identify the first shot timing in that case.