低照度宽幅航空相机系统设计

Design of wide view aerial camera system in low-light

为了满足低照度环境下航空影像信息快速获取的需求,对一种低照度宽幅成像系统进行了研究。基于相机摆扫成像的工作模式,明确了采用大相对孔径低畸变的光学系统,配合真空制冷的低噪声高灵敏度CMOS探测器成像,并通过高速振镜进行扫描像移补偿的技术路线。详细阐述了相机机械构型的设计思路,总结了一套可工程应用的低照度成像能力计算方法。研究了振镜补偿像移的基本原理,并对相机主体框架进行了仿真分析计算。依据该设计和研究结果,完成了低照度宽幅航空相机的加工装配。该相机具有0.1 m (航高1 km)地面像元分辨率,成像照度适应范围为10~100 000 lx,并且在速高比≤0.04时,可实现3倍航高的大收容宽度。系统的成像质量优良,实测镜头在77 lp/mm时,中心视场传递函数大于0.45。实验室和外场飞行试验所获取的图像清晰,对比度和分辨率高,可以满足使用需求。同时,该相机实际包络尺寸为190 mm×140 mm×140 mm,质量仅为2 800 g,具有轻小型的特点。

In order to meet the requirements of quick acquisition of aerial image information in low light condition, a wide view imaging system which can be adapted to low-light environments was studied. Based on the camera working mode of frame-sweep imaging, the technology route of adopting a large relative aperture and low distortion optical system, combining a low-noise and high-sensitivity CMOS detector with vacuum cooling, and compensating the scanning image motion by high-speed steering mirror was clarified. The design ideas of the mechanical configuration of the camera were explained in detail, and a set of calculation methods of imaging capabilities in low-light which can be applied in engineering were summarized. The basic principle of compensating image motion with steering mirror was studied, and the main frame of the camera was simulated,analyzed and calculated. According to the design and research results, the processing and assembly of the wide view aerial camera in low-light were completed. The camera has a ground sample distance(GSD) of 0.1 meters(height 1 km), and adaptable illumination range of 10-100 000 lx, and a large view width of 3 times the height when the speed to height ratio is less than 0.04. The imaging quality of the system is excellent, and test results show that the MTF of the center field of view at 77 lp/mm is greater than 0.45. The images obtained from laboratory and field flight tests are clear, with high contrast and resolution, which can meet the requirements of use. At the same time, the system is 190 mm×140 mm×140 mm in actual size and 2 800 g in weight, which is light and small.