Photographing on Earth in the distance - difficulttask. Catching enough light from an object at a great distance is not easy. And even then the atmosphere will introduce distortions that can spoil the picture; pollution is very disturbing, especially in cities. Therefore, any picture from a distance of several kilometers or so (provided that the camera is fixed high enough to cope with the curvature of the Earth) is extremely difficult to do.
However, in recent years, scientists have begunuse sensitive photodetectors that do a much better job. Such detectors are so sensitive that they can pick up individual photons and combine them into images at a distance of up to 10 kilometers.
What is the maximum range of the camera?
Obviously, physicists never stop atachieved The other day, Zheng-Ping Li and his colleagues from the University of Science and Technology China in Shanghai showed how to photograph objects at a distance of up to 45 kilometers in the smog-sheltered urban environment. Their method uses individual photon detectors in combination with a unique computational algorithm that allows to obtain super-resolution images by combining scattered data points.
New technology is relatively simple in principle. It is based on the lidar method - LIDAR (Light Identification Detection and Ranging): “detecting, identifying and determining the range using light” - illuminates the object with laser light and then creates an image from the reflected light.
Big advantage of this kind of activevisualization is that the photons reflected from the object return to the detector during a certain time window, which depends on the distance. Therefore, any photons that arrive outside this window can be ignored.
This kind of filter drastically reduces noise,which is created by unwanted photons from the environment. And this allows lidar systems to be very sensitive and distance oriented.
To make the new system work even better inurban environment, Zhen-Ping and his colleagues used an infrared laser with a wavelength of 1,550 nanometers, a repetition rate of 100 kilohertz, and a moderate power of 120 milliwatts. This wavelength makes the system safe for the eyes and allows the crew to filter out solar photons that might otherwise overload the detector.
Researchers send and receive these photons withwith the help of a single optical instrument - an ordinary astronomical telescope with a 280 mm lens. Reflected photons are then recorded by a commercial single photon detector. To create a snapshot, scientists scan the field of view using a piezo-controlled mirror that can turn up, down, left and right.
Thus, they can create two-dimensionalImages. But thanks to the control of the photon arrival time, they can pick up photons reflected from different distances to create a three-dimensional image.
The last achievement that was achievedteam, is to develop an algorithm that captures the image together using single-photon data. This kind of computational visualization has come a long way in recent years, allowing scientists to create snapshots from relatively small data sets.
The results speak for themselves. The team installed a new camera on the 20th floor of a building on Chongming Island in Shanghai and sent it to Pudong Civil Aviation Building across the river, 45 kilometers away.
Regular images taken through a telescopeshow nothing but noise. But the new technique allows you to get images with a spatial resolution of 60 cm, on which you can make out the windows of the building. “This result demonstrates the excellent ability of the LiDAR system of single photons in the near-infrared spectrum to distinguish targets through smog,” scientists say.
It should be understood that the main applicationsuch a system will be in the field of observation, recognition and identification of targets. In addition, the device is no larger than a box of shoes, relatively portable.
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