However, supplemental infrared illumination is still required, even for Gen 3 night vision devices, when the light level is extremely low or an agent is working in total darkness.
Regarding infrared illumination, Sgt. William Frazier, supervisor of the Training Bureau for the Philadelphia (Pennsylvania) SWAT team, emphasizes, "Because of existing ambient light, we rarely require infrared illumination in urban SWAT operations. But when you need it, you need it!"
In comparison to night vision devices, thermal imaging devices are independent of the ambient light in the visible and near infrared parts of the spectrum. Thermal devices detect so-called far infrared light, emitted by all objects in the amount that is proportional to the object's temperature, then converts it into an electronic image.
According to Bise, thermal imaging is more complicated to use and interpret. He finds night vision optics relatively user friendly, easy to learn and easy to use in comparison.
Pavsner also notes thermal imaging limits the details in the image. "No sufficient facial details are seen in thermal — just the heat signature — so it's not good for individual identification," he says.
Yet, thermal imaging is the ideal technology for manhunt operations.
"If an escaped inmate is in a wooded area — not hiding in houses — you can spot him fairly quickly using thermal imaging," says Capt. Chad Gilley, CERT commander for the Oklahoma State Penitentiary. "Thermal imaging shows the heat signature left by a recent handprint or a footprint, so you can see footprints glowing with heat if they've crossed over a field at night when the ground is cold."
Thermal imaging also is an important addition to night vision for successful border control. Border control agents are faced with the paradoxical task of halting illegal immigration, while at the same time preventing pain, suffering and possible death of these immigrants should they become stranded in the desert or trapped inside an abandoned vehicle.
"Thermal imaging devices can be used to see through material such as canvas — the type that might be used to cover a truck," explains Pavsner. "Night vision can't see through material to spot warm bodies that might be hiding under a tarp or canvas. On the other hand, thermal cannot see through windows, because the heat bounces off." Due to the limitations of each technology, good border control really requires the best of both.
Chief Ranger Fred Patton of Arizona's Organ Pipe Cactus National Monument concurs. "The thermal imaging technology currently available to us is not yet mobile enough. We can use the thermal devices to locate sources of heat along the border, but our agents need to use image intensified night vision devices to navigate across the desert and investigate the exact sources of these hot spots."
One of the most frequent uses of thermal imaging is search and rescue. Whether it is a child or Alzheimer's patient who has wandered off, or people trapped after a natural disaster, thermal fits the need. "It is great for finding missing people who are still alive," says Daniel Fuller, director of Urban Search and Rescue in Hilton Head, South Carolina. "It's also useful in locating people under rubble when a building has collapsed. When doing search and rescue away from buildings, thermal works best in cold weather because of the dramatic temperature disparity between the missing person and the surrounding area."
Because thermal imagers tend to be more expensive than night vision, some departments have shied away from their use or developed a method to share the technology.
"We have thermal devices strategically located around the state, available to check out on an as needed basis," says Bise.
Rivkin notes that state-of-the-art thermal imaging systems are very mobile and portable. However, these systems are not yet widely available to many users. Helmet and head mounts are available for both thermal imaging and night vision devices.
Monocular vs. binocular