Hyperspectral Image Processing for Target Recognition

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Application of Hyperspectral Imager in Disguised Target Recognition(part 1)

author: Yilia

2023-01-10

Application of Hyperspectral Imager in Disguised Target Recognition(part 1)

In national defense engineering, it is realized by using methods such as camouflage nets and composite materials to perform profiling and imitation color masking; for example, camouflage uniforms are the most traditional camouflage methods. The false display is to confuse observers with false targets through the simulation of real targets, such as using profiling materials to simulate real targets; for example, during World War II, the Soviet Union used a large number of "wooden tanks" to confuse the German army, so that the German army did not dare Make haste. "Imitation" is easy to implement, and generally only needs to be similar in appearance. "True" requires similarity in nature.

Color camouflage: Under traditional conditions, the detection of camouflaged targets mainly relies on white light instruments, while the camouflage of white light instruments mainly relies on similar colors. The closer the colors are, the better the camouflage effect will be. Camouflage uniforms and various colors of paint can be used to camouflage white light instruments.
Multi-spectral camouflage: The camouflage equipment currently used is all artificially synthesized, and its composition is difficult to be completely consistent with natural features. Although the color can be made the same, its spectral characteristics are also quite different from natural features. Since the previous multispectral imaging was limited to a small number of bands, the camouflage equipment such as camouflage nets used was often developed only for these bands, so it could achieve better results under the technical conditions at that time.
Hyperspectral anti-camouflage: With the development of hyperspectral remote sensing technology, the spectral resolution continues to improve. Hyperspectral can simultaneously acquire spectral images and characteristic spectral curves of a certain wavelength of the target, and it has become possible to conduct reconnaissance on hundreds of bands of targets. . Even though objects are similar in color, there are differences in the general spectral curves of different objects. , the existing camouflage equipment will inevitably be detected on a certain band. According to this difference, hyperspectral remote sensing may detect camouflaged targets.

The role of hyperspectral imagers in national defense applications mainly lies in:
1. Detection of camouflaged targets
2. Simulate the local investigation situation, and correct the camouflage measures of one's own side.
Everything has two sides, and remote sensing technology is the same. It brings unprecedented challenges to national defense engineering camouflage, and at the same time provides a new vision and technical means for the development of camouflage technology.

1.1. Typical camouflaged targets in the desert background
Method: Hyperspectral Polarization Imaging
Combat in desert areas is a combat style in a special environment. At present, most of our western theaters are desert areas, so our military high-level attaches great importance to combat training in desert areas, so it is of great significance to study target detection technology for camouflage protection in desert areas. Since the 1990s, in view of the difference in spectral or polarization information between the target and the background, researchers have proposed detection techniques for camouflaged targets in desert backgrounds.

Figure 1. The polarization characteristic model of reflected light

Hyperspectral polarization imaging can obtain multiple information such as space, intensity, spectrum and polarization of the target, and provide richer information support for target detection, thereby improving the accuracy of detection.

In view of the fact that the most commonly used camouflage protection methods in the desert are desert camouflage clothing, desert camouflage nets, armor camouflage coatings, etc., the author developed a sub-aperture simultaneous hyperspectral polarization imaging system to study the desert under different light intensities and different viewing angles. The hyperspectral polarization characteristics of typical camouflage targets in the desert background, such as camouflage nets, desert camouflage plates, tank scale targets, and Humvee scale targets, provide guidance for better detection of camouflage targets in desert backgrounds.

Figure 2 Sub-aperture simultaneous hyperspectral polarization imaging system;

(a)physical map; (b) main field of view location map

It is acquired by a sub-aperture simultaneous hyperspectral polarization imaging system. Figure 2 shows the physical map and the main field of view of the imaging system. The imaging system is composed of three independent and parallel hyperspectral imaging systems with identical structural design and polarization directions of 0°, 60° and 120° respectively.
The block diagram of the internal structure of the sub-aperture simultaneous hyperspectral polarization imaging system is as follows.

1.2. Analysis of hyperspectral polarization characteristics of desert camouflage net

Relative reflectance spectra of desert camouflage nets under different light intensities;

(a)synthetic intensity relative reflectance spectra; (b) polarization relative reflectance spectra

The experimental results show:
1) Under different light intensities, the composite intensity relative reflectance spectrum of the desert camouflage net changes. Under the same detection band, the stronger the illumination, the smaller the composite intensity relative reflectance, and the relative reflectance spectrum of the degree of polarization is similar, but there are differences; 2 ) under different light intensities, the synthetic intensity of the desert camouflage net has a large change relative to the reflectance spectrum, and the polarization degree has a small change relative to the reflectance spectrum, indicating that the polarization degree image of the desert camouflage net has a certain ability to resist light changes;
3) Under different light intensities, the detection bands are in the range of 660-810nm and 820-845nm, the relative reflectance of synthetic intensity of desert camouflage net and the relative reflectance of polarization degree are larger, which is beneficial to the detection and surface properties of this type of desert camouflage net. analyze.

1.3Analysis of Hyperspectral Polarization Characteristics of Desert Camouflage Plate

Relative reflectance spectra of desert camouflage plates under different light intensities;

(a)synthetic intensity relative reflectance spectra; (b) polarization relative reflectance spectra

Under different light intensities, the synthetic intensity relative reflectance spectrum and the polarization relative reflectance spectrum of the desert camouflage plate change. Under the same detection band, the stronger the light is, the smaller the synthetic intensity relative reflectance is, and the greater the polarization relative reflectance is.
Under different light intensities, the synthetic intensity of the desert camouflage plate has a large change relative to the reflectance spectrum, and the polarization degree has a small change relative to the reflectance spectrum, which shows that the polarization degree image of the desert camouflage plate has a certain ability to resist light changes;
Under different light intensities, the relative reflectance of synthetic intensity and the relative reflectance of polarization degree of desert camouflage plates are larger in the detection bands of 470-510nm, 580-675nm, 765-810nm, and 825-845nm, which is beneficial to the Type desert camouflage plate detection and surface property analysis.

The relative reflectance spectrum of the tank scale target under different light intensities;

(a)the synthetic intensity relative reflectance spectrum; (b) the polarization degree relative reflectance spectrum

The experimental results show:
1) Under different light intensities, in the range of 450-770nm, the synthetic intensity relative reflectance and polarization relative reflectance spectra of tank scaled targets change. Under the same detection band, the stronger the illumination, the more synthetic intensity relative reflectance. The larger the relative reflectivity of the degree of polarization is, the larger the degree of polarization is;
2) Under different light intensities, the composite intensity of the tank scaled target has a large change relative to the reflectance spectrum, and the polarization degree has a small change relative to the reflectance spectrum, indicating that the tank scaled target polarization image has a certain ability to resist light changes;
3) Under different light intensities, the detection bands are in the range of 480~540nm, 610~705nm, 765~810nm, 820~835nm, the relative reflectance of synthetic intensity and the relative reflectance of polarization degree of the scaled tank target are large, and there is It is beneficial to scale target detection and surface attribute analysis of this type of tank.

Conclusion: The synthetic intensity relative reflectivity and polarization relative reflectivity of camouflaged targets in the desert background fluctuate with the detection band. By optimizing the detection band, it is beneficial to the detection of camouflaged targets and the analysis of surface properties. The detection band of desert camouflage net should be in the Choose from 660~800nm, the detection band of the desert camouflage plate should be selected from 500~510nm, 580~600nm, 690~800nm, the detection band of the tank scale target should be selected from 480~540nm, 620~650nm, 765~800nm , the detection band of the Humvee scale target should be selected from 630~805nm, 825~835nm.