Abstract
Step/stare imaging with focal plane arrays (FPAs) has become the main approach to achieve wide area coverage and high resolution imaging for long range targets. A fast steering mirror (FSM) is usually utilized to provide back-scanned motion to compensate for the image motion. However, the traditional optical design can just hold one field point relatively stable, typically the central or on-axis field point, on the FPA during back-scanning; all other field points may wander during the exposure due to imaging distortion characteristics of the optical system, which reduces the signal to noise ratio (SNR) of the target. Aiming toward this problem, this paper proposes a non-rotationally symmetric field mapping method for the back-scanned step/stare imaging system, which can make all field points stable on the FPA during back-scanning. First of all, the mathematical model of non-rotationally symmetric field mapping between object space and image space is established. Then, a back-scanned step/stare imaging system based on the model is designed, in which this non-rotationally symmetric mapping can be implemented with an afocal telescope including freeform lenses. Freeform lenses can produce an anamorphic aberration to adjust distortion characteristics of the optical system to control image wander on an FPA. Furthermore, the simulations verify the effectiveness of the method.
Highlights
Modern intelligence, surveillance, and reconnaissance systems strongly require to have wide area coverage and high-resolution imaging abilities
The third-generation infrared search and track (IRST) systems utilize the focal plane arrays (FPAs) with step/stare imaging to achieve wide area coverage
Addressing the problems of off-axis field point wander and image blurring caused by the use of fast steering mirror (FSM) in back-scanned step/stare imaging system, this manuscript proposes a non-rotationally symmetric
Summary
Surveillance, and reconnaissance systems strongly require to have wide area coverage and high-resolution imaging abilities. In certain imaging applications, such as infrared search and track (IRST) systems, it is desirable for the imaging sensor to scan large fields of regard at a high rate and with diffraction limited performance. The third-generation IRST systems utilize the FPAs with step/stare imaging to achieve wide area coverage. Long-wave infrared (LWIR) detectors are not as advanced as MWIR detectors, but they are making significant progress in larger format size and smaller detector pitch [18] In this situation, the sensors with super definitions FPAs and long focal length require tight control on the imaging distortion, and even a single pixel shift may cause too much blur for acceptable system performance. Step/stare and IRST systems are widely applied, but this problem of image blurring due to off-axis field point wander is not well recognized and solved.
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