Projects/Programs

Forensic Topography and Surface Metrology

Summary

We are working to improve the scientific infrastructure for objective forensic firearm and toolmark identification. We focus on the development of measurement methods, objective comparison metrics, and rigorous procedures to obtain quantitative uncertainty estimates for forensic conclusions. This work is part of the project's general mission to advance traceable surface topography measurements in the U.S. by developing methods to characterize and reduce measurement uncertainty and by providing best-in-class calibrations, standard reference materials (SRMs), and reference software.

Description

topography.jpg

three-dimensional topography of a firearm’s breech face

Measured three-dimensional topography of a firearm’s breech face impression on the bottom of a cartridge case. The outer diameter of the donut-shaped area is approximately 4.3 mm.

Forensic firearm and toolmark identification is based on comparing the surface topography of forensic samples, such as fired bullets and ejected cartridge cases. The examiner typically must determine whether microscopic marks on compared surfaces were made by the same firearm or tool. This determination 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 is a fundamental need in forensics for objective, quantitative methods to evaluate the similarity between evidence and reference surfaces so that objective decisions about common origin can be made with uncertainty statements. Therefore:

  • We conduct research to provide a scientific foundation for forensic identification. Our focus is on metrics and algorithms for objective identification, and on rigorous methods to estimate the uncertainty (or error rate) of a forensic conclusion.
  • We collaborate on the characterization and improvement of measurement techniques and on documentary standards for measurement quality assurance. NIST SRM 2460 Standard Bullets and SRM 2461 Standard Cartridge Cases (https://www.nist.gov/pml/engineering-physics-division/surface-and-nanost...) are used in both U.S. and foreign crime labs for quality control. We provide a crowd-sourced, open-access, research database of firearm toolmarks on bullets and cartridge cases (https://www.nist.gov/programs-projects/nist-ballistics-toolmark-database). The database contains both traditional reflected light microscopy images and three-dimensional surface topography data. The data is used internationally for the development and validation of methods for objective identification and error rate estimation.

Surface topography affects the functionality of manufactured parts. To control surface topography, industry requires increasingly advanced measurement methods.

  • The project provides best-in-class calibrations, SRMs, and reference software for surface roughness, step height, and microform. The SI-traceability of most topography measurements in the U.S. relies on this service.
  • We provide surface and microform calibrations with uncertainty levels that are among the world's best. We lead the development of documentary standards, and conduct research to provide a sound basis for optical measurement methods.
  • We provide an interactive website, the Surface Metrology Algorithm Testing System (SMATS), for quantitative assessment of surface topography software. The user can download or upload surface profiles and topography images and compare our calculated parameter values with those obtained by the user's software.

Major Accomplishments

2016

  • Developed a crowd-sourced, open-access, research database of firearm toolmarks on bullets and cartridge cases (https://www.nist.gov/programs-projects/nist-ballistics-toolmark-database). The database has a dynamic web interface enabling users to upload, search, and download datasets. We obtained and measured bullet and cartridge case samples from crime lab reference collections and foundational ballistics studies, such as studies involving consecutively manufactured firearm components and persistence firings.
  • Refined the Congruent Matching Cells (CMC) identification method, including a new convergence algorithm, which improved specificity, sensitivity, and error rate estimation. We developed an approach using a “similarity map” to highlight areas of two compared samples that are highly similar or dissimilar, providing a visual aid to forensic examiners.
  • Completed development and characterization of a replication process for replenishing the sold-out SRM 2460 Standard Bullet. We developed and tested a durable, sputter coated, metal surface layer for the polymer replicas. Produced 115 replica SRM bullets that are currently being certified. We furthermore provided replicas for a major international examiner proficiency study.

2015

  • Initial statistical approach to estimate and express the uncertainty ('error rate') of a firearm identification result obtained using the Congruent Matching Cells (CMC) method.
  • Prototype SRM bullet replicas for quality control of forensic measurements.
  • A series of (draft) ISO standards describing performance parameters and sources of measurement uncertainty for all major optical measurement methods for surface texture – ISO 25178: Parts 601 to 607.

2014

  • NBIC II study established SRM-based procedures for statistical quality control of ballistics toolmark measurements in forensic laboratories.
  • Improved ISO standard for Rockwell hardness indenters based on NIST research results.
  • Prototype NIST Ballistics Toolmark Research Database and characterization of over 1000 forensic samples.

2013

  • Congruent Matching Cells (CMC) method for accurate and objective firearm identification. The method was tested using both topography data and reflectance microscopy images from studies involving consecutively manufactured firearms.
  • Awarded SBIR Phase 2 project to address the need for smooth surface roughness SRMs through development of SRM 2076-2078 "High-precision random profile roughness specimens," with a roughness average (Ra) down to 1/10th of PTB specimens.
  • Characterized the effects of the probe tip size on the measured roughness average (Ra) of specimens with rectangular profiles.
     

Selected Publications

Applying 3D measurements and computer matching algorithms to two firearm examination proficiency tests
Topography measurements and applications in ballistics and tool mark identifications
Validation Tests for the Congruent Matching Cells (CMC) Method Using Cartridge Cases Fired With Consecutively Manufactured Pistol Slides
Selecting Valid Correlation Areas for Automated Bullet Identification Systems Based on Striation Detection
Forensic Science, Ballistics, Nanotechnology, Nanofabrication / manufacturing and Nanometrology

Organizations

Staff

Jun-Feng Song
Zhe Chen
Wei Chu
Thomas Brian Renegar
Richard M. Silver
Johannes A. Soons
Michael T. Stocker
Theodore V. Vorburger
James H. Yen
Nien-Fan Zhang
Xiaoyu Alan Zheng

Contact

Facilities

Specialized Equipment:

  • Talystep stylus instrument for step height measurement (0.04 nm repeatability).
  • Form Talysurf stylus instrument for surface topography measurement (12 mm z-range,1 nm z-resolution, 200 mm x-range, and 0.125 µm x-resolution).
  • Disk scanning confocal microscope and focus variation microscope for three-dimensional surface topography measurements, in particular of forensic samples (down to 3 nm z-resolution). Interferometric microscope for three-dimensional surface topography measurement (phase shifting and coherence scanning).

Specialized, Best-In-Class, Measurement Capabilities:

  • Surface roughness calibrations with nanometer level expanded uncertainty (Ra).
  • Step height calibrations down to 0.15 nm expanded uncertainty.
  • Microform calibration with the world's lowest uncertainty for the microform calibration of standard Rockwell hardness diamond indenters.

Specialized NIST Facilities:

  • Forensic comparison microscope (Special Programs Office).
  • Firing range (Special Programs Office).

Associated Products

  • Surface Metrology Algorithm Testing Service (SMATS)
  • NIST Ballistics Toolmark Research Database
  • NIST microform calibration system for standard Rockwell diamond indenters.  

Customers/Contributors/
Collaborators

Our collaborators are interested in our measurement expertise, unique measurement capabilities, and unbiased standards contributions. Our forensics work is considered to be game changing. Collaborators include:

  • Forensics: ATF, FBI, NIJ, State crime labs, Netherlands Forensic Institute, Leeds Forensic Systems, Cadre Forensics, John Jay College of Criminal Justice.
  • Surface metrology: PTB, NPL, Timken, Federal-Mogul, Professional Instruments, Michigan Metrology, Zygo, Zeiss, Bruker, Apple, UNCC, Worcester Polytechnic.
Created April 19, 2013, Updated May 30, 2017