- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
In the long-wave infrared radiation band (8–12 μm), the environmental radiation greatly affects the infrared signature of aircraft. The main aim of this paper is to assess the effects of atmospheric and ground radiance on the infrared signature of a cruise aircraft flying at high altitude. Firstly, the computation method of infrared signature is presented. The reverse Monte Carlo ray tracing method is applied to evaluate the effect of environmental radiation on the infrared signature of aircraft. The MODTRAN code is used to compute the atmospheric/ground radiance and atmospheric transmittance. Then, this method is validated with experimental data. Finally, the effect of environmental radiation on infrared signature of aircraft is discussed with the consideration of atmospheric condition, flight altitude, flight speed, and the emissivity of the airframe skin. The results show that the infrared signature of the lower surface of the aircraft is sensitive to the environmental radiation whose reflection contributes more than 20% to the total radiation at Mach 0.9. Increasing flight altitude, reducing atmosphere temperature and reducing flight speed will increase the ratio of reflected environmental infrared radiation intensity to total infrared radiation intensity of the aircraft. After considering the environmental radiation, the reduction amplitude of infrared signature of the aircraft by reducing the surface emissivity is decreased. The infrared signature of the aircraft lower surface is still significant compared to environment, even though the emissivity of the aircraft surface is reduced.
The reflected environmental radiance is an important part of the aircraft infrared signature in the long-wave band. The effect of the reflected environmental radiation on the infrared signature of a cruise aircraft is related to the atmosphere condition, the flight speed, the flight height, and the emissivity of the airframe surface. The effect of atmospheric radiation on the infrared signature of the lower part of the longitudinal detection plane is the largest, followed by the lateral detection directions and the upper part of the longitudinal detection directions. The effect of reflected ground radiation on the infrared signature of aircraft is similar to that of atmosphere radiation. Increasing flight altitude (from 7 km to 11 km), reducing atmosphere temperature (from summer to winter) and reducing flight speed will increase the RRT (ratio of re- flected environmental infrared radiation intensity to total infrared radiation intensity) of aircraft. The reflected environmental radiance (sum of atmospheric radiance and ground radiance) accounts for more than 20% of the total radiation of a basic aircraft with a speed of Mach 0.9 in the straight downward direction, and more than 10% of the total radiation in the lateral detection directions. The computational results show that the long-wave band radiation temperature of the aircraft decreases significantly with the reduction of the surface emissivity. But the amplitude of reduction is reduced if the environmental radiation is considered. For an aircraft flying at Mach 1.2, if airframe surface emissivity decreases from 0.85 to 0.35, the reduction amplitude with considering the environmental radiation is about 54% of that without considering the environmental radiation. The radiation temperature of the aircraft lower surface is still significantly higher than that of the aircraft upper surface and background, even though the emissivity of the aircraft surface is as low as 0.35.