Miniature Thermal Imaging Cameras for Firefighting Applications

The ability to detect the temperature differences of objects is vitally important to firefighters, who must often open doors that lead to fires and identify the seat and extension of a fire quickly and reliably. This palm-sized thermal imaging camera (TIC), the Omega(TM), has a very wide scene dynamic range. This is critical because the camera can be pointed in the direction of a very hot fire, yet still produces a useable image of the colder surroundings or personnel without saturation.

Smoke has a large component of micron-sized carbon soot particles in it, making it very absorbing in the visible-light waveband. However, when the particle size is significantly smaller than the wavelength of light used by a sensor, the scattering is greatly reduced, making it possible to see through smoke.

The infrared sensor, based on vanadium oxide microbolometer technology, is a 160 × 128 pixel focal plane array (FPA) that images in the 7-14 micron (longwave IR) waveband and does not require ternperature stabilization, thus eliminating the thermoelectric cooler (TEC) found in other microbolometer cameras. Proprietary read-out circuitry in the Omega FPA and novel non-uniformity correction algorithms make operation without a TEC possible. Also, the camera package utilizes a very specialized flex board technology that folds up like an accordion inside the metal camera case. This technology eliminates many connectors that would add size and cost and reduce reliability.

A version of this camera has been successfully integrated into the Evolution® 5000 TIC fire service tool manufactured by Mine Safety Appliances (MSA) in Pittsburgh, PA (Figure 1). The Omega(TM) provides the Evolution® 5000 with 14-bit scene dynamic range, and uses a non-linear histogram AGC algorithm called SmartScene(TM) to map the 14-bit range to an 8-bit analog video display. It also has two gain states, which are automatically selected according to the percentage of pixels in the image that go above or below a threshold value. This enables it to operate in the extreme environments that firelighters regularly encounter, such as a dark wet basement and a burning room.

The Evolution® 5000 takes advantage of the Omega camera's Isotherm display option, which allows users to tint every pixel at a certain temperature or within a temperature range a specific color. Figure 2 shows an image of a firefighter in a burning room. The yellow pixels correspond to temperatures above 842 0F, and the red pixels to temperatures above 887 °F. The scene temperature, measured by the spot meter denoted by the green dot in the center of the image, is read out on the bar indicator on the right of the image. The bar indicator changes color to indicate high or low gain mode. The "L" indicator tells the user that the TIC is in low sensitivity or "firefighting" mode. This lower sensitivity mode extends the dynamic range of the TlC and is particularly useful in fire service where scene temperatures can be extremely wide.