Backscanning step and stare imaging system with high frame rate and wide coverage.

Step and stare imaging with staring arrays has become the main approach to realizing wide area coverage and high resolution imagery of potential targets. In this paper, a backscanning step and stare imaging system is described. Compared with traditional step and stare imaging systems, this system features a much higher frame rate by using a small-sized array. In order to meet the staring requirements, a fast steering mirror is employed to provide backscan motion to compensate for the image motion caused by the continuously scanning of the gimbal platform. According to the working principle, the control system is designed to step/stare the line of sight at a high frame rate with a high accuracy. Then a proof-of-concept backscanning step and stare imaging system is established with a CMOS camera. Finally, the modulation transfer function of the imaging system is measured by the slanted-edge method, and a quantitative analysis is made to evaluate the performance of image motion compensation. Experimental results confirm that both high frame rate and image quality improvement can be achieved by adopting this method.

Motion profile and control design of fast steering mirror for backscanning step and stare imaging.

Fast steering mirrors (FSMs) have been used for decades to improve the performance of electro-optical imaging systems, such as airborne imaging systems and space-based optical surveillance systems. With the advantage of increasing the accuracy of image motion compensation and the efficiency of scanning imaging, backscanning step-and-stare imaging has become the main approach to realizing wide-area surveillance for airborne imaging systems. According to the operating mode and motion profile of the FSM in the imaging system, a combined optimized profile (COP) is designed to avoid abrupt changes in the velocity and acceleration of the FSM. The angular position sensor based on a four-quadrant detector is used in FSMs to expand the measuring range and cut the cost at the expense of larger measurement noise. Combining a Kalman filter with a disturbance observer and zero-phase error tracking control, a control method is proposed to improve the control precision and bandwidth while suppressing measurement noise. Simulation and experimental results show that the profile designed by COP is smooth enough to meet the special requirements of FSM's backscanning image motion compensation and that the Kalman filter-based FSM control method can significantly improve the control accuracy.