This project provides methods, standards, and services for characterizing surface texture and microform in manufacturing, forensics, and science. We seek to advance SI-traceable measurements by developing methods to characterize and reduce measurement uncertainty, and by providing best-in-class calibrations, standard reference materials (SRMs), and reference software. A major application area addressed by the project is forensic firearm and toolmark identification, which is based on comparing microscopic marks in the topography of forensic samples. Here we contribute to the scientific infrastructure needed for objective forensic evaluations by developing traceable measurement methods, objective comparison metrics, and statistically rigorous procedures to obtain quantitative estimates for uncertainty or weight of evidence.
Surface texture affects the functionality of many products, ranging from bearings to semiconductors and optics. Affected properties include aesthetics, friction, wear, lubrication, sealing, light scattering, and conductivity. Improvements in parameters and metrology to characterize surface texture enable innovations and facilitate commerce. Major challenges are the large variety of applications, the large number of parameters available to specify and characterize surface texture, and the large array of mechanical and optical measurement techniques. The project seeks to advance SI-traceable metrology of surface texture and microform through:
Forensic firearm and toolmark examination is based on comparing the surface topography of forensic samples, such as fired bullets and ejected cartridge cases. When a firearm is fired, it leaves microscopic toolmarks on the bullet and cartridge case. Forensic examiners compare these marks to determine whether two cartridge cases or bullets were fired from the same firearm. Currently, this evaluation is subjective, relying on an examiner’s expertise and judgement. The evaluation is challenging, not only because there are differences between marks generated by the same firearm, but also because there are possible similarities between marks generated by different firearms. There are two major shifts occurring in this forensic area: 1) a transition from two-dimensional (2D) reflectance microcopy images of toolmarks to three-dimensional (3D) topography images, and 2) a desired transition from subjective match/no-match assessments to objective comparisons with a rigorous evaluation of uncertainty to quantify the weight of evidence. We address these challenges through: