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Electro-Optical Infrared Technology for Naval Vessels
Electro-Optical Infrared Technology for Naval Vessels
Electro-optical infrared (EO/IR) technology converts visible light and invisible infrared radiation into electronic signals that can be analyzed.electro optic infrared These signals can reveal threats even in total darkness and through atmospheric obscurations such as rain, fog or smoke. By integrating EO/IR capabilities with radar, naval vessels can detect and respond to threats in all conditions of visibility.
Unlike radar, which uses active radiation to transmit and receive return signals from targets, EO/IR sensors are passive.electro optic infrared EO/IR sensors detect infrared signatures naturally emitted by target objects and analyze those signatures using algorithms that look for specific characteristics of the object such as size, shape and motion. This allows the sensor to recognize and identify a threat even in complete darkness, through clouds, or during periods of high-velocity air turbulence.
The EO/IR imaging system consists of the detector array, a spectral filter to select the spectral band in which the signal is measured, and the read-out electronics that process and provide data for output.electro optic infrared Depending on the application, the detector may be either uncooled or cooled. Uncooled systems are typically based on silicon, while cooled systems use materials such as InGaAs and HgCdTe.
In order to make an image, the detector samples all of the incident energy that falls on it and then uses a reconstruction algorithm to produce a final image.electro optic infrared The noise and aliasing that are introduced by sampling must be accounted for in performance analysis. In general, the performance of a sensor is limited by its ability to reconstruct an image correctly within one instantaneous field of view (IFOV).
Several factors need to be considered when testing a EO/IR system.electro optic infrared These include target-background contrast, the intensity of the target thermal emission, operating altitude and visual range.
Another key issue is the ambient optical transmission of the spectral region in which the EO/IR system operates. This can be a significant factor, particularly in airborne applications. Optical transmission through the atmosphere is less than that of glass, which can significantly degrade imaging performance. This is especially true for systems operating in the SWIR band. Consequently, the ability of a system to see through windows and windshields is an important consideration.
The performance of a spectral filter is also a critical factor in an EO/IR system. A spectral filter selects the wavelength in which it is effective and filters out other wavelengths. The resulting image is degraded by the loss of energy in other wavelengths, which can be corrected for using sophisticated optical models and digital signal processing algorithms.
One of the challenges of evaluating a spectral filter is that the performance is dependent on the temperature at which it is operated. This leads to the need for a temperature stabilized system, which can have significant Size, Weight and Power (SWaP) implications at the sensor level. Recently, there has been a considerable effort to develop spectral filters that can be used without cryogenic equipment. This is possible by using so-called III-V superlattices, which are composed of alternating layers such as aluminum gallium arsenide and hafnium gallium arsenide that allow the spectral response to be adjusted by changing individual layer thicknesses.
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