Longwave Ultraviolet Forensics Imaging Applications Dr. Austin Richards Oculus Photonics June 25, 2012
What is longwave ultraviolet radiation? UV is a waveband, a range of colors of the EM spectrum UV is invisible to human eyes it has no color that human beings can describe. Images are displayed in black and white. For the UV waveband, one describes different colors of the EM spectrum by their wavelength. We use the nanometer or nm unit to describe wavelength in the UV band. The UV band can be broken into two main categories: near-uv and shortwave UV The longwave UV band as 300nm-400nm. The shortwave UV band is 200-300nm Both the longwave UV and the shortwave UV wavebands can be used to greatly enhance the contrast in crime scene images. They can be used to quickly find evidence that is invisible both to the unaided eye and to ALS examination. The method is non-destructive and non-invasive. Evidence can be documented without physical contact or alteration. DNA evidence can then be recovered without the problems of contamination or dilution from contact methods.
Why? Both these bands of UV tends to be absorbed by materials much more than visible light. If you light up a crime scene with UV rays, and image the UV that is reflected off the scene with a UV camera, you will see things the eye can t see. Note the distinction this is not the same as UV fluorescence. Here UV goes in,uv comes back out and is imaged. Longwave UV imaging can greatly enhance contrast in a crime scene image. Some examples: Dusty shoeprints on a floor (without the need for dust lifters) Bloody fingerprints on a table (without the need for processing) Cleaning marks on surfaces (where blood was cleaned up) Saliva, water and other fluids staining or marking surfaces Old bitemarks and other pattern injuries on skin after they have faded Repainted body panels on cars (showing repairs made after a hit-and-run accident)
Oculus Photonics UVScanner This is a longwave UV viewer with LCD displays for both eyes, dual near-uv illuminators on top, and rubber eyecups to block ambient light, permitting UV imaging in bright light. A variety of lenses options are available.
How is the UVScanner different from RUVIS? RUVIS is primarily a short-range method, restricted to a few feet at most. This is because of the high degree to which the light sources based on gas-discharge lamps spread out. Longwave UV imaging can take advantage of very bright LED-based light sources. These forensic flashlights can put out several watts or more of 365nm UV light. This enables a much wider area to be examined quickly, and from much farther away, with greater safety. An investigator can flood an entire floor and look for trace evidence very quickly.
Imaging a wide area : Water splashes on a wood floor The area in the image is about 2 feet wide by 2 feet deep. The illumination is 365 nm UV light from a Clearstone Technologies light source.
How is the UVScanner different from RUVIS? RUVIS requires shortwave UV illumination (254 nm wavelength). This radiation is very irritating to the eyes and the skin. Full face masks and Tyvek suits must be worn in areas that are highly illuminated with shortwave UV radiation. The longwave UV sources are much safer to work around. They are 365 nm wavelength. UV safety glasses and sunscreen on exposed skin are more than enough protection for long-duration exposure.
How is the UVScanner different from RUVIS? The UVScanner uses a special silicon CCD video camera to produce analog video that is fed to dual near-eye LCD displays. The dual displays are much less fatiguing to use for extended periods compared to looking into a RUVIS device with one eye. While in use, the UVScanner can be connected to a standard NTSC video monitor or recording device like a mini-dv recorder for training and evidence collection via a video cable. Oculus Photonics also makes a UV imaging module that converts a Canon camcorder to near-uv operation. The package is called the UVCorder and was our first product. The camcorder can record both color HD video and UV video from the module. One can record one or the other, but not both at the same time.
UVCorder UV video camera Longwave UV handheld solution: Oculus Photonics UVCorder This is a longwave UV imaging system that can capture video and displays a live image. The system has a longwave UV illuminator on top. It has a wavelength of 396 nm.
Ultraviolet Forensics Imaging Applications
UV imaging applications There are two main categories of UV imaging applications in forensics: Seeing invisible surface features due to enhanced absorption Seeing invisible features due to enhanced scattering In other words, you get more absorption of UV radiation by trace evidence than with visible light. The evidence is easier to see with a longwave UV camera than with the unaided eye. Other types of trace evidence scatter UV rays much more than they scatter visible light. Again, you can see the evidence much easier.
UV absorption UV photons have more energy than visible (VIS) and infrared (IR) photons Many materials and substances that reflect VIS and IR will absorb UV light. The higher energy makes this happen. The shorter the wavelength of UV, the stronger the absorption This property of UV makes invisible materials visible
UV absorbers Organic molecules found in body fluids tend to absorb UV. You can see fingerprints and bloodstains. Metals and inorganic materials (like cement and tile) tend to reflect UV If you have an organic material on an inorganic substrate, you can often get enhanced contrast with UV compared to regular color or infrared forensic photos
Bloody fingerprints Visible light Courtesy of Rachel Leintz, Phoenix PD
Bloody fingerprints Longwave UV (365nm illumination) Courtesy of Rachel Leintz, Phoenix PD
Human saliva on wood floor Saliva and other liquids are easy to see against various substrates Visible light Longwave UV (365nm illumination)
Human saliva on wood floor Visible light Longwave UV (365nm illumination) The wood surface finish is opaque to the UV. The wood grain is thus hidden, making it much easier to see surface detail.
Human saliva on wood floor Visible light Longwave UV (365nm illumination) Even very tiny droplets of saliva are apparent in the UV image. These can be sampled for DNA evidence. The longwave UV illumination is much less damaging to DNA than the shortwave UV used by RUVIS, so this is a better search method.
White car door looks normal to the eye uniform tonality to the paint VIS Longwave UV (365nm) The longwave UV image shows that the paint has been compromised Courtesy of Heidi Nichols, Miami-Dade County Medical Examiner s Office
Repainted fender on Prius This fender was replaced Visible Light Fresh paint absorbs UV more strongly than older oxidized paint 330-400nm
Original painted fender on Prius Visible Light 330-400nm The other side shows equal absorption by the paint
Repainted ceiling covering blood spatter Visible light Longwave UV (365nm illumination) The whiter paint is old paint. The fresh paint absorbs UV more strongly.
Cleaning marks on ceiling (where blood was cleaned off) Visible light Longwave UV (365nm illumination) The cleaning products leave a slight residue that absorbs UV
Cleaning marks on ceiling (where blood was cleaned off) Visible light Longwave UV (365nm illumination)
Fresh paint near bottom of wall Fresh paint absorbs UV Visible Light 330-400nm
Old and Faded Bite mark Visible Light Longwave UV These photos were taken 5 months after the victim was bitten. The bite mark causes the skin to produce excess pigment on the wound site. Longwave UV imaging increases the contrast significantly relative to visible light. Courtesy of Stephen Warlen, Kansas City PD
Enhanced scattering of UV
Seeing surface texture with UV imaging Since UV tends to be absorbed at the surface of materials, one can sometimes see surface texture This works even when the surface is translucent or transparent to VIS and IR In addition, UV light waves have shorter wavelengths compared to visible light. UV light rays thus get scattered by surface scratches and imperfections much more readily than visible light rays.
Ultraviolet bite mark images Visible light Longwave UV Bruising makes the toothmarks very hard to see in the visible-light image The UV image on the right shows the tooth impressions much better as there is much less penetration of the UV light into the skin
Dusty shoeprint on wood flooring visible light image Visible light Courtesy of Rachel Leintz, Phoenix PD
Dusty shoeprint on wood flooring near-uv image Longwave UV (365nm illumination) Courtesy of Rachel Leintz, Phoenix PD
Visible light Courtesy of Rachel Leintz, Phoenix PD
Longwave UV (365nm illumination) Shoe is Naturalizer brand Courtesy of Rachel Leintz, Phoenix PD
Visible light Courtesy of Stephen Warlen, Kansas City PD
Courtesy of Stephen Warlen, Kansas City PD
Visible light Courtesy of Stephen Warlen, Kansas City PD
Courtesy of Stephen Warlen, Kansas City PD
Shoeprint on waxed vinyl floor The pressure of the shoe changes the texture of the wax and changes how it reflects UV light Visible Light 396nm UV