RECOVERY OF DEFACED SERIAL NUMBERS USING INFRARED THERMAL IMAGING

As submitted by the proposer: Stamped serial numbers in engines and firearms provide a means of identification; however, they can be removed for criminal activities. Although these can in some instances be restored by chemical etching, the discovery of a non-destructive technique to carry out the restoration is desirable. This project investigates the use of infrared thermal imaging as a non-destructive restoration technique for defaced stamped and laser engraved serial numbers. Infrared thermal imaging of metal surfaces provides thermal images sensitive to local differences in thermal conductivity of regions of plastic strain existing below a stamped number. These strains are created from stamping pressures distorting the atomic crystalline structure of the metal as well as melted material from laser engraving and extend to depths beneath the stamped number. The construction and implementation of instrumentation for three types of thermographic techniques utilizing an infrared camera to image the heat flow over these strained areas to recover residual traces of defaced numbers is proposed. Transient infrared thermography, pulsed infrared thermography and lock-in infrared thermography are all sensitive to localized changes in the thermal conductivity of a material and have been used to image defects in diverse materials. They are sensitive to localized plastic strains and thus should make nondestructive recovery of the numbers possible. The basis of the instrumentation setup is an infrared camera with a rapid response time which can detect differences in the temperature of material in the strained or melted regions brought to the surface when overlying serial numbers are removed, and differences in the phase of a thermal wave as it passes through these regions.

These thermal differences may not be visible from the raw thermal images and further enhancement needed to pick up the subtle variations. Sophisticated multivariate image analysis techniques will be used to enhance the recovery. MIA procedures will be employed on the data collected to reconstitute images of the original serial numbers using the temperature variation across the surface as a function of time. Quarterly milestones include construction and testing of the equipment as well as their implementation in recovery of stamped and laser engraved serial numbers from steel and aluminum alloys which are characteristic of materials usually seen in forensic investigations. A final technical report suitable for dissemination to forensic practitioners will be made outlining the results of these studies and making recommendations for best practices based on scientific data collected during the investigation.

This project contains a research and/or development component, as defined in applicable law. nca/ncf.

Stamped serial numbers in engines and firearms provide a means of identification; however, they can be removed for criminal activities. Although these can in some instances be restored by chemical etching, the discovery of a non-destructive technique to carry out the restoration is desirable.

This project investigates the use of infrared thermal imaging as a non-destructive restoration technique for defaced stamped and laser engraved serial numbers. Infrared thermal imaging of metal surfaces provides thermal images sensitive to local differences in thermal conductivity of regions of plastic strain existing below a stamped number. These strains are created from stamping pressures distorting the atomic crystalline structure of the metal as well as melted material from laser engraving and extend to depths beneath the stamped number.

The construction and implementation of instrumentation for three types of thermographic techniques utilizing an infrared camera to image the heat flow over these strained areas to recover residual traces of defaced numbers is proposed. Transient infrared thermography, pulsed infrared thermography and lock-in infrared thermography are all sensitive to localized changes in the thermal conductivity of a material and have been used to image defects in diverse materials. They are sensitive to localized plastic strains and thus should make nondestructive recovery of the numbers possible. The basis of the instrumentation setup is an infrared camera with a rapid response time which can detect differences in the temperature of material in the strained or melted regions brought to the surface when overlying serial numbers are removed, and differences in the phase of a thermal wave as it passes through these regions. These thermal differences may not be visible from the raw thermal images and further enhancement needed to pick up the subtle variations. Sophisticated multivariate image analysis techniques will be used to enhance the recovery. MIA procedures will be employed on the data collected to reconstitute images of the original serial numbers using the temperature variation across the surface as a function of time. Quarterly milestones include construction and testing of the equipment as well as their implementation in recovery of stamped and laser engraved serial numbers from steel and aluminum alloys which are characteristic of materials usually seen in forensic investigations. A final technical report suitable for dissemination to forensic practitioners will be made outlining the results of these studies and making recommendations for best practices based on scientific data collected during the investigation.

This project contains a research and/or development component, as defined in the applicable law.

nca/ncf