Without this advanced stereo camera, according to the traditional technical scheme, three cameras need to be installed on the satellite to take photos of the same point on the moon surface from three angles. However, this will increase the weight of the payload, thus adding a series of technical difficulties to the launching capacity of rockets, the size and weight of satellites and other supporting facilities, and limiting the carrying of more scientific detection equipment on satellites. At the same time, this CCD stereo camera has improved its adaptability to the space environment with the miniaturization and lightweight of the equipment.
At present, the number of moon stereo photo photographed in the world is limited and incomplete. If this lunar exploration goes well, we can see a series of stereo photo with full moon topography and landforms photographed by China people.
Of course, for scientists, the value of the three-dimensional image data of the moon is far more than letting everyone see the geomorphological pictures of the moon. According to these three-dimensional images, scientists will divide the structure and geomorphic units of the lunar surface, make the outline map of the lunar fracture and ring images, outline the evolution history of the lunar geological structure, and study the origin of the moon and the universe. At the same time, these images will also serve the second and third lunar exploration projects in China, including providing scientific basis for the next lunar rover and astronauts to land on the moon.
Chang 'e No.1 stereoscopic glasses
The so-called three-dimensional mapping is an all-round mapping of the surface of an object. At present, the mainstream surveying and mapping methods in the world are stereo observation, radar interferometry and laser scanning surveying and mapping. Among them, stereo observation technology is the most mature, and its research history is over 100 years. Undoubtedly, it is also the preferred universal technology for lunar stereo mapping in various countries. Stereoscopic observation is to obtain three-dimensional information by using the visual principle of left and right parallax of human eyes. Chang 'e-1 carried 1 CCD stereo camera and 1 laser altimeter, forming 1 pair of "stereo glasses".
Brief introduction of stereo camera
Because the surface of the moon is uneven, the plane images taken by ordinary cameras can't get the image data in the depth direction of the line of sight, so stereo cameras are needed.
Stereo camera is the key part of stereo imaging. Because it is difficult to touch in daily life, ordinary people may be unfamiliar with stereo cameras, but in fact this technology has been born for a long time. As early as in ancient Greece, Euclid had discovered that people's left and right eyes saw different scenes, which was the main reason why people could gain insight into three-dimensional space. In modern terms, binocular parallax is the basic principle of stereoscopic images.
Stereo imaging can be divided into static scene shooting and dynamic scene shooting. To shoot a static scene, you only need to use a camera, first take a photo at a certain position and angle, and then move the camera in parallel for a certain distance before taking another photo, and you can get a set of stereo photo with parallax. To shoot a dynamic scene, you need to use a special stereo camera (such as a dual-lens camera), or two cameras can take two photos at the same time.
Early stereo imaging technology mainly relied on traditional cameras to shoot a group of stereo photo, and used stereoscope to reproduce stereo images. Because the traditional stereoscopic photography is complicated to make and difficult to circulate, it is limited to professional photography and a few special fields, and it can't go deep into all levels like traditional plane photography. With the rapid development of science and technology and the appearance of CCD digital cameras, the technology and application of stereoscopic images have made breakthrough progress.
Charge coupled device camera
CCD (Charge Coupled Device) is an important part of stereo camera. It is a photosensitive semiconductor device, and the photosensitive unit on it converts the received light into an amount of charge, which is proportional to the intensity of the incident light. In this way, an area CCD composed of photosensitive cells arranged in a matrix can sense images. CCD is now widely used in digital cameras and video cameras, as well as astronomical telescopes, scanners and bar code readers.
Many innovative technologies have been adopted in the development of the CCD stereo camera used in Chang 'e-1, such as large-field optical system and large-area CCD chip. It uses one camera instead of three cameras, which can realize three-dimensional imaging of the subject. When the stereo camera works, the output of CCD is collected to obtain forward-looking, forward-looking and backward-looking images respectively, and then processed to form a stereo image. CCD stereo camera works in self-propelled scanning mode. In order to reconstruct the three-dimensional image of the lunar surface, special processing has been done in the design.
When the satellite flies, the CCD stereo camera sweeps the lunar target along the flight direction, and images of the lunar target at three different angles can be obtained. Because the stereo camera is fixed on the satellite, it can't rotate freely, but moves with the relative movement between the satellite and the moon to scan the surface of the moon. This CCD stereo camera also improves its adaptability to the space environment through miniaturization and light weight of the equipment, and reduces the weight of the payload, which makes it difficult to realize a series of technical problems such as the launching ability of the rocket, the volume and weight of the satellite and the transformation of other supporting facilities.
At present, the number of stereo photo of the Moon existing in the world is limited and incomplete. If this lunar exploration can be successfully completed, then we can get a vivid all-moon terrain stereo photo.
Obtaining a complete three-dimensional image of the moon not only allows everyone to see the landscape of the moon, but also has far-reaching research value. According to these three-dimensional images, scientists can divide the structure and geomorphic units of the lunar surface, make the outline map of the lunar fracture and ring images, sketch the evolution history of the lunar geological structure, study the origin of the moon and the universe, and provide scientific basis for the lunar rover and astronauts to choose the landing site next. We look forward to seeing the true face of the moon as soon as possible!
The history of stereoscopic photography
Stereo photography technology originated in 1930s in 19, and Wheatstone invented the stereo mirror in 1838. Stereoscope consists of two mirrors that are perpendicular to each other. The left picture and the right picture are placed on the photo holder respectively. Rotate the joystick to adjust the photo to a suitable position to watch the stereoscopic image.
1839, Daguerre invented the silver plate photography, which not only laid the foundation of photography, but also promoted the vigorous development of stereo photography.
1849, David Brewster replaced the mirror in the stereo with a convex lens and invented an improved stereo.
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