Simulation of infrared polarized radiation transmission characteristics of high-temperature tail flame based on Monte Carlo method

Infrared polarization radiation of aircraft targets after being transmitted through high-temperature exhaust plumes is an important basis for infrared detection equipment to detect, identify, track and warn aircraft. At present, most of the studies on the transmission characteristics of gas polarized radiation focus on the visible wavelength band, and the research object is mainly the atmospheric environment. The study of infrared polarization radiation transmission characteristics in the special gas environment of high-temperature exhaust plume is still insufficient. In this paper, the Monte Carlo method is used to model the transmission of infrared polarized light in a high-temperature exhaust plume, and the absorption coefficients of H<sub>2</sub>O in 2.5−3.3 μm band and CO<sub>2</sub> in 4−5 μm band are calculated using the HITRAN database. The multiple scattering process of photons in the exhaust plume space is simulated, and the changes of the cosine of motion direction and cosine of vibration direction of the photons in the collision events are analyzed at the microscopic level. Additionally, the photon characteristics are statistically analyzed based on the principles of calculating polarization and transmittance. Based on the simulation results, the changes of radiative transmittance and polarization at different transmission distances are compared with each other, and the effects of exhaust plume temperature, pressure, gas component concentration, and detection wavelength on the transmission characteristics of infrared polarized light are analyzed as well. The experimental results demonstrate that the error between the calculated radiative transmittance in this study and the HITRAN database is within 2%. The effects of temperature and pressure on the transmission characteristics of polarized light become increasingly significant as the distance increases. The pressure is negatively correlated with transmittance and polarization, while the effect of temperature is related to the gas type and the temperature range. The radiant transmittance and polarization degree decay exponentially with the absorption coefficient and transmission distance of the gas in the exhaust plume space. Different detection wavelengths also lead to differences in the transmission characteristics of polarized light.