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In the inclement pneumatic calefaction condition, the window of IR imaging system will be calefied and emit infrared
radiation, so that the Signal-to-Noise and quality of target IR image are felled off that are from the imaging system. At
this rate the physical characteristic of IR window direct affect capability of imaging system controlled and guided
homing by IR tracker and measure precision of target IR characteristics.
The properties of sapphire make it an ideal choice for the high speed missile applications compared to other existing or
emerging materials. But the research has not been reported about the infrared radiation characteristic of sapphire as the
IR window.
In this paper, based on an IR imaging system using the sapphire window, the experimentation and conclusions of IR
thermal image measurement affected by IR window's pneumatic calefaction have been accomplished. Firstly, the
temperatures of sapphire window at supersonic flight extended over 1 km and 15 km from the ground have been
estimated by calculating the flow and state variables and the aerodynamic heating into the window. On the base of the
results calculated the window static state calefaction experimentation and electric arc wind tunnel experimentation had
been designed and completed to validate the effect degree of pneumatic calefaction to the imaging system.
With the temperatures of the sapphire window rising, in the image coming from the imaging system, the peak luminance
of target image detected is increased, the background average luminance of the image is also increased, and the margin
of above two varies in a little range.
The data obtained from the different temperature experimentation have demonstrated that the IR flux due to the sapphire
window becomes heated by friction with the air and heat transfer to the dome can obscure the target image created by the
onboard IR sensor, depress Signal-to-Noise and resolving power of the imaging system, but can not overload the
detector.
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