Research progress of correlation imaging under outdoor environment

Image, as a method of information acquisition, is indispensable for human beings, and it plays an irreplaceable role in military and civilian fields, such as detection and scouting, precision guidance, transportation, and industrial production. In the outdoor environment, the resolution, signal-to-noise ratio, and working distance of optical imaging are limited as result of the influence of background light, stray light, and atmospheric medium. In recent years, with the development of muti-discipline such as optics, physics, information theory, and computer science, the new optical imaging technologies continue to emerge, thus bringing new opportunities for outdoor optical imaging towards long-distance, large field of view and high information flux. As one of the new active imaging technologies, correlation imaging has the potential applications of robustness against turbulence and noise, and the possibility of beating the Rayleigh limit. It can deal with the problems better, such as sharp attenuation of optical power caused by long distances, detection of interference signals from environmental noise, and influence of turbulence. Based on the principle of optical imaging, this paper analyzes the factors affecting optical imaging, in terms of resolution, signal-to-noise ratio, spatial bandwidth product, and imaging distance under outdoor environment, focusing on the research progress of outdoor correlation imaging including imaging systems, signal-to-noise screening technology and imaging algorithm. In addition, we analyze the requirements of optical imaging for longer distances and broader field of view, and consider the fundamental problems and the key technologies.