# Visual Navigation Systems for Maritime Smart Ships: A Survey
## 3 Visual Perception Navigation Technology
### Single Perception
#### 3.1.3 Infrared  
Infrared technology (IRT), or IRT for short, is an advanced navigation aid technology that detects and recognizes objects based on their thermal radiation properties. The technology uses infrared sensors to capture the thermal radiation signals emitted by the target object, and by analyzing the wavelength, intensity and distribution of these signals, it realizes the precise measurement of the target's position, speed and shape. Its high-precision detection capability enables ships to navigate the sea more safely and efficiently.  
Infrared technology is applied in the form of infrared thermometers, infrared spectrometers, infrared communication devices, etc., and infrared cameras are major tools in the application of infrared technology for sensing and thus assisting navigation systems, so we mainly analyze the research on the technology related to infrared cameras. [PERSON] et al. (2021) proposed a robust foreground detection method based on background modeling combined with multiple features in the Fourier domain (BMMFF) for ship target detection in dynamic sea-surface backgrounds, which outperforms the relevant comparable algorithms in different challenging sea-surface scenes [96]. When the weather at sea is clear, the maritime target is located exactly between the sunlight and the infrared camera, and the gray value of the background of the infrared image is larger than that of the target. [PERSON] et al. (2019) designed an infrared maritime target detection algorithm based on the Visual Attention Model (VAM), which improves the accuracy and efficiency of the search for maritime targets in backlit environments [97]. In order to improve the target tracking efficiency of ships, [PERSON] et al. (2022) proposed an efficient method of SiamRPN++ based on cross-connected and spatially transformed networks of AlexNet, which effectively improved the method to 63.9 FPS [98]. Infrared thermal imaging technology has been widely used in the field of target detection. It can not only adapt to different light-intensity environments; at the same time, it has the characteristics of strong concealment, strong detection ability, long detection distance and high detection sensitivity. [PERSON] et al. (2023) proposed an improved Canny segmentation algorithm based on the maximum interclass variance method on the basis of infrared thermal imaging, which stabilized the flow field of background light to achieve the effective segmentation of a ship's image and obtained a high-definition operational target [99]. In addition to the above advantages, infrared technology also has an inherent advantage in small-target detection. [PERSON] et al. (2023) took the lightweight model of infrared small-ship detection as the research object, constructed an infrared small-ship dataset and preprocessed the images using gamma transformation, and the model parameters were reduced by 83% compared with the YOLOv5m model [100]. To compensate for the limitations of radar and AISs, such as blind spots and limited detection ranges, [PERSON] et al. (2024) utilized an infrared radiometric camera to supplement conventional perception sensors which is capable of accurately detecting obstacles at sea and estimating their dynamic motions based on enhanced tracking results [101].