# Multi-Band Polarization Imaging in a Harsh Sea Fog Environment
## 4 Experimental Results and Analysis  
### Analysis of the Effect of Multi-Band on Polarization Imaging  
In this experiment, multi-band imaging experiments were performed using the SALSA camera in a sea fog environment with an optical thickness of 0.75, which was obtained by a solar radiometer. Subsequently, the multi-band polarization images were calculated by processing the intensity images in a MATLAB2014a environment. In Figures 6-8, Figure (a) shows the multi-band intensity images of the sea spray environment with the bands at 670 nm, 530 nm, and 450 nm, respectively, and Figure (b)-(d) show the polarization images, line polarization images, and polarization angle images of the corresponding bands obtained at 670 nm, 530 nm, and 450 nm, respectively. Figure 5: Polarization imaging at three wavelengths in varied weather **a**. Sunny weather, **b**. Sea fog environment (**a**) 670 nm (**b**) 530 nm (**c**) 450 nm. Figure 6: 670 nm band image (**a**) Intensity images (**b**) Polarization images (**c**) Line polarization images (**d**) Polarization angle images. From Figures 6-8, it can be intuitively seen that the intensity image is blurred, the imaging gray value is high, a lot of information is covered, the contour details are not obvious enough, and the target edge information cannot be clearly seen, which is due to the different absorption and scattering effects of sea fog particles on different wavelengths of light in the complex sea fog environment, resulting in more background noise when imaging. Since the polarization degree image is more effective than the polarization angle image, the edge contour information of the plant can be seen, and the line polarization degree image is less effective than the darker one and has less representation of the details. Therefore, this paper focuses on the polarization degree image. Since the contrast of an image can intuitively reflect the observer's perception of the image, the image contrast equation is known according to the Weber-Fechner law as follows [16]. \[C_{W}=\frac{I_{t}-I_{b}}{I_{b}} \tag{23}\]  
where \(C_{W}\) is the target background contrast of the intensity image, \(I_{t}\) denotes the target area brightness, and \(I_{b}\) is the overall brightness of the background area of the image. Figure 9 above shows the results of the contrast experiments based on the acquired multi-band intensity images and polarization images of the imaging target in the sea fog environment. Compared to the standard intensity picture, polarization has a powerful fog-transparent capacity to emphasize the target's outlines, which may significantly increase the target's contrast. When the contrast of the target polarization image at 450 nm is 7.1%, it has the lowest contrast compared to the other two bands. Compared with the other bands, the contrast of the polarization image obtained by processing is larger than the contrast of the intensity image when the band is 530 nm, and the rise in the value between the contrast is larger compared with the rest of the bands. With the increase of wavelength, the contrast of the polarization image increased by 1.4% at 670 nm compared with that at 450 nm. This is because the scattering intensity is inversely proportional to the wavelength, meaning that the longer the wavelength, the less likely it is to be scattered. When the contrast value of the polarization image was the largest, compared with the polarization image of the rest of the band, the difference between the target and the background in this band was the largest, which was more suitable for the observation of the target. Figure 8: 450 nm band image (**a**) Intensity images (**b**) Polarization images (**c**) Line polarization images (**d**) Polarization angle images. Figure 7: 530 nm band image (**a**) Intensity images (**b**) Polarization images (**c**) Line polarization images (**d**) Polarization angle images. Figure 10 shows the evaluation indexes of polarization images at 670 nm, 530 nm, and 450 nm.