Low cost FTIR imaging method sheds light on footware for forensics
A technique known as Frustrated Total Internal Reflection (FTIR) imaging has led to a new method of creating a digital picture of a person’s footprint.
Dr James Sharp at the School of Physics and Astronomy at The University of Nottingham is working with the East Midlands Special Operations Unit – Forensic Services (EMSOU-FS) in the UK to develop FTIR imaging for forensic analysis of footwear.
The study, ‘Watch your step! A frustrated total internal reflection approach to forensic footwear imaging’, has been published in the open access journal Scientific Reports.
FTIR in this study operates by measuring the change in refractive index of light when a shoe comes in contact with an illumination waveguide made of glass or acrylic that the person walks on. Cameras then image that light from below.
Conventional FTIR has been used in the past to map the imprint of bare feet on a hard surface by shedding light through a transparent sheet of material as the foot hits the ground and reflecting it back at an angle. Using the same technique Dr Sharp’s research group has created more detailed images of the ridges on the sole of a shoe and how these contact a hard surface.
A person’s gait determines weight distribution as they walk, which, in turn, leads to specific wear and tear on the soles of their shoes. Although specific wear patterns would not necessarily be able to identify a person as the perpetrator of a crime as readily as a fingerprint or DNA, it could be used to link them, or at least their shoes, to a particular location – information that could be vital to the police.
Dr Sharp said: ‘This technique uses ideas taken from A-level physics to form images of regions where shoes contact surfaces. The low cost and ease of implementation of the technique make it particularly appealing for forensic applications. We are currently in the process of working with local police forensic laboratories and the [UK] Home Office to try to develop this work further.’
EMSOU-FS and The University of Nottingham are looking to test a finished product within a criminal justice setting in the coming months.
In addition to forensics, the footwear analysis technique could potentially be used for applications such as clinical studies of gait or measuring how athletes interact with surfaces during high impact activities such as jumping, running or changing direction.