The National Institute of Standards and Technology Standard Reference Materials (SRM) 2460 Standard Bullets and
2461 Standard Cartridge Cases are intended for use as check standards for crime laboratories to help verify that their
computerized optical imaging equipment for ballistics image acquisitions and correlations is operating properly. Using
topography measurements and cross-correlation methods, our earlier results for the SRM bullets and recent results for
the SRM cartridge cases both demonstrate that the individual units of the SRMs are highly reproducible. Currently, we
are developing procedures for topographic imaging of the firing pin impressions, breech face impressions, and ejector
marks of the standard cartridge cases. The initial results lead us to conclude that all three areas can be measured
accurately and routinely using confocal techniques. We are also nearing conclusion of a project with crime lab experts to
test sets of both SRM cartridge cases and SRM bullets using the automated commercial systems of the National
Integrated Ballistics Information Network.
In some automated bullet identification systems, the similarity of striation marks between different bullets is
measured using the cross correlation function of the compressed signature profile extracted from a land impression.
Inclusion of invalid areas weakly striated by barrel features may lead to sub-optimal extraction of the signature profile
and subsequent deterioration of correlation results. In this paper, a method for locating striation marks and selecting valid
correlation areas based on an edge detection technique is proposed for the optimal extraction of the compressed signature
profiles. Experimental results from correlating 48 bullets fired from 12 gun barrels of 6 manufacturers have
demonstrated a higher correct matching rate than the previous study results without correlation area selection processing.
Furthermore, an attempt to convert a traditional profile with multiple z-quantization (or gray scale) levels into a binary
profile is made for the purpose of reducing storage space and increasing correlation speed.
Based on the cross-correlation function (CCF), a new parameter called profile difference, Ds (or topography difference
for 3D), is developed for measurement and comparison of 2D profiles and 3D topographies. When Ds = 0, the two
compared profiles or topographies must be exactly the same (point by point). A 2D and 3D topography measurement
system was established at the National Institute of Standards and Technology (NIST), that includes data acquisition
stations using stylus instruments and a confocal microscope, and a correlation program using the proposed parameter Ds
and the cross-correlation function maximum CCFmax. This system has been used for 2D and 3D ballistics signature
measurements of the NIST Standard Reference Material (SRM) 2461/2461 Standard Bullets and Casings, and received high measurement reproducibility. It is suggested that the proposed parameter and algorithm can be generally used for measurement and comparison of 2D and 3D surface topographies in surface metrology and other areas.
Based on auto- and cross-correlation functions (ACF and CCF), a new surface parameter called profile (or topography) difference, Ds, has been developed for quantifying differences between 2D profiles or between 3D topographies with a single number. When Ds = 0, the two compared 2D profiles or 3D topographies must be exactly the same (point by point). A 2D and 3D topography measurement system was established at NIST. This system includes data acquisition stations using a stylus instrument and a confocal microscope, and a correlation program using the proposed parameters Ds and the cross-correlation function maximum CCFmax. Applications in forensic science and surface metrology are described; those include profile signature measurements for 40 NIST Standard Reference Material (SRM) 2460 standard bullets, and comparisons of profile measurements with four different techniques. An approach to optimizing the Gaussian filter long wavelength cutoff, λc, is proposed for topography measurements.