Physicist Zheng-Pin Lee and his colleagues from the Chinese University of Science and Technology in Shanghai developed a photograph of tens of kilometers even in the city. The urban environment is very unfavorable for such work – there are many parasitic
Light sources, evaporation, etc.D. The presence of mobile objects and environmental pollution — also leaves its mark;But it is in cities that a large -scale monitoring system is needed at large distances.
The basis of the installation is an innovative photon Lidar – a detector capable of catching a single photon. For example, as part of an impulse reflected from the target, to measure the distance by the time of return. The device is sensitive enough to see the objects at a distance of 10 km, but the team went on and assembled the installation on the basis of the telescope, which sends and takes photon bundles at a distance of 20, and at the limit of capabilities and 45 km.
The system uses an infrared laser with a wavelength of 1550 nanometers, a frequency of 100 Kilortz and a capacity of only 120 millivatts. It is safe for the eyes and allows you to put experiments in the city line. The main merit of Chinese scientists —In the development of the strobing algorithm: they learned to calculate the “temporary window” of the return of photons from the goal and according to these data, all other parasitic photons are cut off. Including sunlight, which creates the main problem in such observations. As a result, where ordinary optics shows continuous noise, the features of the object begin to manifest itself.
The accuracy of the camera is amazing-when shooting from the roof of a 29-storey skyscraper on the island of Chongming, Shanghai, the testers accurately calculated the number of windows in the airport building in Pudun, about 45 km from them. And, in addition, improved the resolution of the system from the previous minimum indicator of 1 m to 60 cm. And all this using equipment that is placed in a container the size of a shoe box! Whether his colleagues now intend to overcome the bar of 100 km, as well as improve algorithms – if you correctly vary the strob, you can display the measurement results immediately in the form of three -dimensional models.
Source — Arxiv.Org