In defense and global security electro-optical systems whether for surveillance, situational awareness, or targeting, daylight cameras are combined with cameras optimized for other portions of the light spectrum such as a Long Wave Infrared LWIR (thermal) camera, a NIR camera (low light) and a SWIR camera to obtain full motion video throughout the day and night. The thermal camera or image-intensified camera allows the operator to easily detect anomalies in a scene. Other cameras such as the SWIR or the visible camera can then be used to recognize or identify the anomalies.
The proliferation of these mission critical systems in recent years is a result of heightened security concerns, and surveillance has been intensified at airports, seaports, in cities, at borders, etc. The large increase in military and global security systems has been fueled by the need to persistently observe wide areas, navigate unmanned vehicles, increase distance from danger, improve accurate targeting, and more on fixed, airborne and ground-based platforms. These goals have been supported by advances in image sensors and cameras as well as the increase in available bandwidth.
There are efforts in both the military and other global security areas to increase the resolution of imaging systems from VGA to HD and digital to meet the video intelligence goals and other networking needs. There have been many advances in image sensors and latest generation sensors enable the full HD resolution with real-time or faster frame rates as well improved sensitivity in low light conditions.
Previously the daylight or video camera was only useful in daylight situations but with new technologies now available it is possible to use the daylight cameras in low light situations to complement the other cameras in the imaging system. The image sensor technology is so good that the daylight and low light capabilities can be combined in one daylight camera.
The technologies for thermal, SWIR and image intensified cameras are not available in full HD yet (resolution of 1920 x 1080). This is an additional reason for increased importance of the daylight camera. The ability to identify in low light conditions is greatly facilitated by having color available from the daylight camera.
The use of advanced daylight cameras with low-light capabilities offers several benefits including:
- Increased identification capabilities in low light conditions (dusk, dawn, fog, etc.) through full HD resolution color video
- Additional detection capabilities in night conditions
- Reduced total number of cameras in electro-optical systems
- Reduced SWAP, complexity, and cost
There is no consensus in the world about a uniform definition of scene conditions and light levels. Low light is used to describe a variety of conditions, but in Figure 1 we provide our definition of low light scenery conditions.
Daylight cameras will not be able to replace image-intensified cameras since these can be used in extremely low light conditions (below 1 mLux). Our definition of low light daylight cameras is those that offer sensitivity in the mLux level. This would give the user visibility in a no-moonlight night sky.
Figure 1. Low Light Scene Illumination Definition
Special imaging technologies have been utilized to improve the abilities to “see” in the night such as image intensifiers, EMCCD, EBCCD/EBCMOS, and InGaAs (SWIR) range. As mentioned before, image intensified cameras do not enable identification and InGaAs SWIR cameras are not in full HD, limiting the identification capabilities. EBCCD/EBCMOS are only available in monochrome, run at very high voltages and have blooming/halo effects at overexposures.
This all leaves a gap for low light identification through full HD, which can now be served by uncooled, proven CCD-based rugged daylight camera options because of the advances in CCD image sensors. For more information about the available cameras, see: TMX-DHD rugged cameras