title: Short range shooting distance estimation using variable pressure SEM images of the surroundings of bullet holes in textiles.
abstract: Modifications of cotton and polyester textiles due to shots fired at short range were analyzed with a variable pressure scanning electron microscope (VP-SEM). Different mechanisms of fiber rupture as a function of fiber type and shooting distance were detected, namely fusing, melting, scorching, and mechanical breakage. To estimate the firing distance, the approximately exponential decay of GSR coverage as a function of radial distance from the entrance hole was determined from image analysis, instead of relying on chemical analysis with EDX, which is problematic in the VP-SEM. A set of backscattered electron images, with sufficient magnification to discriminate micrometer wide GSR particles, was acquired at different radial distances from the entrance hole. The atomic number contrast between the GSR particles and the organic fibers allowed to find a robust procedure to segment the micrographs into binary images, in which the white pixel count was attributed to GSR coverage. The decrease of the white pixel count followed an exponential decay, and it was found that the reciprocal of the decay constant, obtained from the least-square fitting of the coverage data, showed a linear dependence on the shooting distance.
authors.affiliation: PGCiMat Programa de Pós Graduação de Ciência dos Materiais, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, 91501-970 Porto Alegre, RS, Brazil; Instituto de Geociências, UFRGS, Brazil. Electronic address: ruth.hinrichs@ufrgs.com.
authors.forename: Ruth
authors.initials: R
authors.lastname: Hinrichs
authors.affiliation: PGCiMat Programa de Pós Graduação de Ciência dos Materiais, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, 91501-970 Porto Alegre, RS, Brazil; Instituto Geral de Perícias do Rio Grande do Sul, Departamento de Criminalística IGP-RS-DC, Brazil.
authors.forename: Paulo Ricardo Ost
authors.initials: PRO
authors.lastname: Frank
authors.affiliation: PGCiMat Programa de Pós Graduação de Ciência dos Materiais, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, 91501-970 Porto Alegre, RS, Brazil; Instituto de Física, UFRGS, Brazil.
authors.forename: M A Z
authors.initials: MAZ
authors.lastname: Vasconcellos
keywords: GSR coverage; Image segmentation; Shooting distance estimate; Textile fiber modification; Variable pressure scanning electron microscope