With the continuing development of photoelectric detection technology, infrared polarization technology offers significant advantages, such as cloud penetration and target recognition. Infrared polarization technology has been widely used in stealth, anti-stealth, and military camouflage. The camouflaged target may be more accurately detected using infrared polarization detection since it shows substantial polarization radiation features in the infrared range. In contrast, coating the surface with a depolarization coating can effectively diminish its polarization characteristics, thereby creating a target camouflage. Therefore, investigating the characteristic polarization modeling of camouflage coatings can aid in the effective generation of camouflage and anti-camouflage for the target. Most of the shading functions utilized in the current polarization bidirectional reflectance distribution function (pBRDF) are blind simplified models that do not correspond to the actual rough surface elements. Consequently, it is necessary to conduct shading function research consistent with the real scenario. Research on the polarization characteristics of coatings in the extended infrared band, in particular, is still in its infancy and requires further investigation.

In this work, an improved shading function model is adopted, and the specular reflection coefficient and diffuse reflection coefficient are introduced to characterize the polarized radiation characteristics of the camouflage coating surface using the Priest-Germer (P-G) model. A two-component pBRDF optimization model is established, and a linear polarization degree model of infrared radiation is derived. The numerical calculation results of the model are compared with the experimental data, and the effects of the surface roughness, geometric attenuation, and diffuse reflection on the infrared polarization degree of the coating surface are analyzed numerically. Additionally, the effect of environmental radiation on the infrared polarization characteristics of the coating is analyzed.

The numerical results of the proposed infrared polarization model are compared with the experimental data, and the slope of the curve after linear fitting is 0.9924 (Fig. 4). The linear polarization degree model reflecting the geometric attenuation and diffuse reflection effects is analyzed. The results show that the larger the surface roughness of the coating, the smaller the infrared polarization degree (Fig. 6). The more significant the geometric attenuation and diffuse reflection effects, the lower the infrared polarization degree of the coating (Fig. 7). When the ambient radiation ratio is less than 1, that is, when the spontaneous radiation is dominant, the lower the ambient radiation ratio, the higher the degree of linear polarization of the coating. When the ambient radiation ratio is higher than 1, the ambient radiation becomes dominant, and the higher the ratio, the lower the degree of linear polarization of the coating (Fig. 8). When the ratio of the coating radiation intensity to the background radiation intensity is closer to 1, the infrared polarization degree of the coating reduces.

The geometric attenuation model established in this study can effectively eliminate the sharp inflection point of the blind model and ensure that the model does not exhibit larger amplitudes at large incident angles, improving the accuracy of the model. Considering the geometric attenuation and diffuse reflection effects, the calculation results of the linear polarization degree is consistent with the experimental data. The greater the surface roughness of the coating, the lower the infrared polarization degree; the more significant the geometric attenuation effect, the lower the infrared polarization degree of the coating. The diffuse reflection effect is negatively correlated with the infrared polarization degree of the coating, and the contributions of geometric attenuation effect and diffuse reflection effect are elucidated. Different linear polarization degrees are obtained with the change in the incident zenith angle, and the peaks of the linear polarization degrees of the camouflaged coatings appear between 70° and 80°. When the ratio of the ambient radiation of the coating is closer to 1, the degree of linear polarization is lower. The conclusions above provide theoretical support for camouflaged coatings in infrared polarization stealth and anti-stealth coatings. Because of the limitations of theory and space, many areas in this study still require further improvement. For example, the effects of volume/surface scattering on the surface-polarized radiation characteristics of infrared coatings are ignored in this study. Further research should be conducted, considering volume/surface composite radiation modeling.