This paper establishes a method for evaluating the visible light stealth effect of small surface targets for visual reconnaissance from the perspective of image similarity. The method is used to quantify and analyze the effect of visible light stealth and monochromatic coating on a typical small surface target. The results show that the proposed method can generate a reasonable response to the structural similarity, texture similarity, color similarity and second-order statistical moment, etc. for small surface target images with different visible light stealth states, and obtain a reasonable magnitude. Therefore, the comprehensive similarity considering the above factors is finally determined as the basis for determining the stealth effect.
Optical camouflage painting, as a basic measure against optical reconnaissance and optical sighting weapon attack, is a general method of optical camouflage of small vessels. By utilizing this method, we can design the camouflage pattern according to basic features of vessel background, paint the camouflage pattern to equipment target surface with camouflage coating, and imitate the natural background or the outline of segmentation targets in color and texture, thus reducing the exposure signs of equipment targets. Due to the fact that most of existing qualitative evaluations on camouflage effectiveness are quantitative evaluation or evaluation based on experts' judgment, this paper put forward a new evaluation method of optical camouflage effectiveness of marine target based on target identification probability and similarity between the target and the background, carried out practical measurement test on optical camouflage effectiveness of marine targets, and calculated quantitative camouflage evaluation results of 50 collected images according to actual contribution of feature indexes. A mathematic relation model of optical identification probability and similarity of marine targets was built after comparison with manual interpretation results of identification probability. The results indicate that: the higher the similarity, the lower the identification probability. If the target and background are totally different, the corresponding target identification probability is 1, which indicates that the lower the similarity, the more the exposure features of the target, and the easier the target to be detected; if the target and background are similar, the corresponding target identification probability is 0, which indicates that the higher the similarity, the less the exposure features of the target, and the more difficult the target to be detected.
In recent years, the attenuation characteristics of log-normal water spray in the infrared region of atmospheric window have been studied in depth. However, there is no report on the comparison between calculation of the infrared transmittance of water spray based on Mie scattering using the LNMCM method and experiment, and the calculation error has not been publicly discussed. In this paper, we used Fluent to calculate the droplet concentration of water spray formed by a square arrangement of four FF-12 nozzles. After the water droplet number density distribution was obtained, the LNMCM method was used to calculate the infrared transmittance of water spray formed by the four-mounted FF-12 nozzles. On the other hand, an infrared attenuating test platform was built with four FF-12 nozzles, and an infrared imaging measurement test was conducted on the water spray formed by the four-mounted nozzles and the test panel that was shielded by it. The article compares the calculated results with the experimental results. Error analysis shows that the calculated value of the infrared radiation intensity of 7.5~13μm deviates from the experimental value by 3.1%. This paper verifies the accuracy of LNMCM and Fluent to calculate the infrared transmittance of log-normal distribution water spray through test measurement method, and forms a relatively complete calculation method of infrared radiation and attenuation of water spray.
The symplectic multi-resolution time-domain(SMTD) scheme with cylindrical grids is developed for electromagnetic simulation. Based on Daubechies' scaling functions and sympletic propagation technique, equations are implemented. In cylindrical coordinates, some singular areas are analyzing and solving. In different stencil sizes, the stability and dispersion property is investigated and it turns out that SMTD is better than FDTD for stability restriction and medium discretization. Perfectly matched layer(PML) absorbing boundary conditions (ABC's) are derived for cylindrical SMTD grids. The numerical simulations validate that SMTD and PML are effective, so this paper may provide a new solution for electromagnetic simulation of cylindrical objects.