Objective The early warning of target is realized according to the single difference of infrared radiation scattering characteristics between target and background for traditional space-based optical detection methods. However, due to the interference of many factors such as ultra-long-distance, complex ambient light, earth background clutter, atmospheric transmission attenuation, infrared imaging system diffraction, nonlinear sampling effect, etc., the radiation difference between the target and the background is easy to be confused by the temperature-based infrared imaging technology, which leads to low target detection rate and large false alarm. As a new detection method, infrared polarization detection can provide more target information than traditional infrared detection. Therefore, the exploration of space-based optical detection methods based on multi-dimensional optical information coupling of target radiation and polarization is of great significance to improve the performance of target detection.

Methods The optical information of infrared radiation and polarization is comprehensively considered. A multi-dimensional imaging feature prediction model for aerodynamic heating targets in orbit under complex sea background is explored. The research results will provide theoretical basis for stable and correct space-based detection of aerodynamic heating targets. Based on the heat transfer and polarization characteristics of the target, the polarization emission and pBRDF model of the aerodynamic heating target are established. The radiation polarization model of the aerodynamic heating target skin is established. Based on Landsat8 remote sensing data, the sea surface temperature (SST) is retrieved. The Cox-Munk pBRDF model and self-polarization model of sea surface are combined to establish the sea surface background radiation polarization model. The second simulation of a satellite signal in the solar spectrum - vector (6SV) model is used to calculate the effect of atmospheric particles on the upward polarization radiation transmission of targets. The physical modulation effect of space-based optical platform is comprehensively considered, and the prediction model of full-chain multi-dimensional optical imaging features of aerodynamic heating target in orbit is established. The imaging characteristics and detectability of the target in orbit at different flight altitudes and detection angles are analyzed by simulation.

Results and Discussions The signal-to-clutter ratio (SCR) decreases with the increase of the detection angle at S₀ and S₁ polarization angles. At S₂ polarization angle, the SCR gradually decreases as the detection angle increases from 10° to 30°, and the SCR appears a peak value when the detection angle is 40°. However, the SCR gradually decreases as the detection Angle continues to increase. Meanwhile, the SCR increases gradually with the increase of target flight height at different polarization angles (S₀, S₁, S₂). The increase value of the SCR with the target flight height at S₀ polarization angle is smaller than that at S₁ and S₂ polarization angle(Fig.8). Therefore, the results show that the space-based optical detection method based on infrared polarization information can suppress the sea surface flare and highlight the target in the direction of the strong reflection of the sun incident light from the sea surface in 3-5 μm.

Conclusions In view of the optical detection requirements for wide area continuous surveillance of aerodynamic heating targets, the detection method based on the space based multi-dimensional optical information of the aerodynamic heating target is studied. An accurate prediction model of the optical radiation polarization imaging feature of the full chain including the aerodynamic heating target-the sea surface-the environmental atmosphere-the optical system-the imaging detector is established. The characteristics of radiation polarization at different detection angles, target flight heights and flight speeds are simulated and analyzed. The results show that in the 3-5 μm band, the target is easier to detect under space-based platforms when the radiation and polarization information are used simultaneously. The results of this paper provide data support for the development of intelligent algorithms for realizing the detection, tracking and identification of targets in the geostationary orbit.