New developments in cooled mercury cadmium telluride (MCT or HgCdTe) infrared detector technology have made possible the development of high end infrared cameras for use in numerous demanding thermal image resolution applications. These infrared cams have become available with unreal sensitivity in the shortwave, mid-wave and long-wave unreal bands or alternatively in two bands. In addition, a variety of camera resolutions are available therefore of mid-size and large-size detector arrays and various pixel sizes. Also, camera features now include high frame rate imaging, adaptable exposure time and event triggering enabling the record of temporal thermal incidents. Sophisticated processing algorithms are available that bring about an expanded dynamic range to avoid saturation and enhance sensitivity. These infrared digital cameras can be calibrated so that the output digital values correspond to article temperatures. Non-uniformity correction methods are included that are independent of exposure time. These performance functions and camera-features permit a variety of cold weather imaging applications that were previously difficult. D3400
At the heart of the high-speed infrared camera is a cooled MCT detector that gives extraordinary sensitivity and versatility for viewing high-speed thermal events.
1. Infrared Spectral Sensitivity Bands
Because of the availability of a variety of MCT detectors, high speed infrared cameras have been designed to operate in a number of distinct spectral rings. The spectral band can be manipulated by ranging the alloy composition of the HgCdTe and the detector set-point temperature. The result is just one music group infrared detector with incredible quantum efficiency (typically above 70%) and high signal-to-noise ratio able to find extremely small levels of infrared signal. Single-band MCT detectors typically fall in one of the five nominal spectral bands shown:
– Short-wave infrared (SWIR) cameras – obvious to 2. 5 micron
– Broad-band infrared (BBIR) video cameras – 1 ) 5-5 micron
– Mid-wave infrared (MWIR) cameras – approximately for five micron
– Long-wave infrared (LWIR) cameras – 7-10 micron response
– Incredibly Long Wave (VLWIR) cams – 7-12 micron response
In addition to digital cameras that utilize “monospectral” infrared detectors which may have an unreal response in one music group, new systems are being developed that utilize infrared detectors that contain an answer in two bands (known as “two color” or dual band). Examples include video cameras having a MWIR/LWIR response covering both 3-5 micron and 7-11 micron, or alternatively certain SWIR and MWIR bands, or even two MW sub-bands.
Presently there are a variety of reasons motivating the selection of the spectral music group for an infrared camera. For certain applications, the spectral radiance or reflectance of the objects under observation is what establishes the best spectral strap. These applications include spectroscopy, laser beam viewing, diagnosis and alignment, target unsecured personal analysis, phenomenology, cold-object image resolution and surveillance in a marine environment.
Additionally, a spectral band may be selected due to dynamic range concerns. Such an prolonged dynamic range would not be possible with an infrared camera imaging in the MWIR spectral range. The wide dynamic range performance of the LWIR system is easily the result of comparing the flux in the LWIR band with this in the MWIR band. As computed from Planck’s curve, the distribution of flux credited to objects at broadly varying temperatures is smaller in the LWIR group than the MWIR group when observing a landscape having the same target temperature range. Put simply, the LWIR infrared camera can image and measure background temperature objects with high sensitivity and resolution and at the same time extremely hot objects (i. e. > 2000K). Image resolution wide temperature ranges with an MWIR system would have significant challenges because the signal from warm objects would need to be drastically attenuated ensuing in poor sensitivity for imaging at background conditions.