With the increase of flight speed, infrared (IR) seeker may be seriously affected by high temperature shock-layer in front of dome. Shock-layer radiance is produced by molecular processes and has implications for sensor waveband selection. This paper examines the impacts of high temperature shock-layer IR radiance from a molecular radiometry point of view. We derived the mathematical expressions of rotational quantum number of maximum intensity and the corresponding wavenumber of P and R branch. The theoretical calculation and the simulation based on HITRAN database are conducted. Results show that with the increasing of temperature, the rotational quantum number of maximum intensity will be larger. Ultimately, the wavenumber of P and R branch moves towards long wavelength and short wavelength direction respectively. The conclusions subserve to select sensor waveband.
In order to study the optical transmission and radiation characteristics in a hypersonic shock layers over infrared optical window, an approximation calculation approach is proposed. With this method, the formal solution for shock layer radiative transport equation is derived considering both target signature and windows thermal radiance. Consequently, the transmissivity of heating shock layer can be expressed quantitatively, which shows that the shock layer is optically thick in the 4~4.5μm band mainly. Besides, the radiance flux density of shock layer is calculated when temperature is 800K, pressure is 7atm and thickness is 1cm. Shock layer radiance is found to be larger in the mid-wave infrared band compared with long-wave infrared band and short-wave infrared band.
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