# Research on the Auto-Exposure Method of an Aerial TDI Camera Based on Scene Prediction  
[PERSON]  
1 Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China; [EMAIL_ADDRESS] (J.H.); [EMAIL_ADDRESS] (X.W.)  
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[PERSON]  
1 Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China; [EMAIL_ADDRESS] (J.H.); [EMAIL_ADDRESS] (X.W.)  
2 Key Laboratory of On-Orbit Manufacturing and Integration for Space Optics System, Chinese Academy of Sciences, Changchun 130033, China  
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[PERSON]  
1 Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China; [EMAIL_ADDRESS] (J.H.); [EMAIL_ADDRESS] (X.W.)  
2 Key Laboratory of On-Orbit Manufacturing and Integration for Space Optics System, Chinese Academy of Sciences, Changchun 130033, China  
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[PERSON]  
3  
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technology to begin to rise; this is known as Time Delayed and Integration (TDI) [8; 9]. At present, this technology, whose basic principle is to expose the same scene multiple times and add up the exposed images, has been widely used in push and sweep aerial cameras [10; 11; 12].  
The shooting distance of aerial remote sensing cameras is usually relatively long, and the radiation energy of ground scenes will be attenuated after passing through the atmosphere and lens [13]. In order to obtain more radiation energy under the condition of low illumination, the direct method increases the exposure time, but a longer exposure time increases the fuzzy quality of image motion [14; 15]. Therefore, by using TDI technology, more radiation energy can be obtained without increasing the exposure time. In aerial TDI cameras, TDI CCD, which is a time-delayed integral charge-coupled device, is usually used as the sensor [16], as it can obtain high-sensitivity, high-resolution, and large-dynamic-range images using TDI technology under the condition of low illumination [17].  
With the development and progression of science and technology, semiconductor technology is becoming more and more precise, and the difficulties in manufacturing aerial remote sensing cameras are increasing; therefore, improving image quality is one of the problems to which researchers have been committed [18]. There are many factors affecting the image quality of aerial remote sensing cameras [19], one of which is exposure; this is the main reason for the decline in image quality under the condition of low illumination, as this determines the degree of light energy absorption of the cameras, changes the overall gray value of the image, and affects the visual effect and information in the image. Auto-exposure aims to obtain the information of the target scene in advance, and uses this as the basis for determining parameter exposure, which can avoid the loss of image information caused by overexposure or underexposure. The auto-exposure of TDI CCD is usually difficult, as the shooting mode of TDI CCD is push and sweep, which can only take one image of the target scene, and the output image is not repetitive, so it is difficult to obtain the image of the target scene in advance. At present, the common method is to add an additional sensor to collect the feature information of the target scene in advance; however, this increases the complexity of the system [20; 21].  
In order to achieve auto-exposure in aerial TDI cameras, this paper studies the imaging link model, and proposes that the camera uses TDI CCD to collect the first N rows of data of the target scene in advance as the basis, and then adjusts and determines the exposure parameters with the median gray value as the target; thus, in the case where there are no additional sensors, the auto-exposure of TDI CCD can be realized.