Design principle
A person needs a tape measure to measure height; what tools are needed to measure “height” on the surface of the moon? The researchers explained that their tool is an infrared laser. By measuring the time and angle of the beam from the satellite to the surface of the moon, scientists can calculate the relative height of a certain point. Connect the dots one by one, and the topographic map of the moon will be on the paper.
Introduction
This laser altimeter has a small appearance and light weight. It can measure topography with an accuracy of 5 meters in an orbit 200 kilometers from the surface of the moon. ". Researcher Wang Jianyu, director of the Shanghai Institute of Technical Physics, said that by then the "Chang'e-1" satellite will also take a plan view of the moon. After adding the relevant "height indicators", all data will be processed by the ground application system to obtain a three-dimensional surface of the moon. Stereo Photo".
There are two main types of topography on the surface of the moon. One is a basin made of solidified lava, which scientists call the "Moon Sea". The largest one has an area of 5 million square kilometers; the other is dotted. , Overlapping craters. The first sample of the laser altimeter developed by Shanghai scientists over the course of two years has undertaken the task of “alternating” for these terrains.
The laser altimeter will follow the "Chang'e-1" satellite to lift off. "Chang'e-1" is China's first lunar exploration satellite and is expected to be launched before 2007. Its detection targets include obtaining three-dimensional images of the lunar surface, analyzing the content of useful elements on the lunar surface and the distribution characteristics of material types, detecting the thickness of the lunar soil, and observing the space environment between the earth and the moon.
Classification
Laser altimeters can be divided into airborne laser altimeters and spaceborne laser altimeters according to the different platforms they carry.
According to the different objects it detects, it can be divided into the earth science laser altimeter system, the Mars orbiter laser altimeter and the moon observer laser altimeter.
Usage
The laser altimeter can be installed on test platforms such as airplanes and satellites. It is mainly composed of three parts: laser emitting module, laser receiving module and data processing module. The laser light emitted by the laser emission module is first hit on the ground, ice on the ocean surface and other detection targets, and then reflected by the target back to the test platform such as airplanes or satellites. The laser receiving module receives the reflected light signal and converts it into an electrical signal. The data processing module will accurately measure the time from the laser emission to the laser altimeter receiving the laser, and this time is the transmission time of the laser in the atmosphere. During this time, the distance traveled by the laser is the distance between the altimeter and the detection target Twice.
According to the propagation speed of light in the air, the size of this distance can be calculated. According to the air height of the laser altimeter, the altitude of the detected target can be finally obtained. Because the laser beam has a small divergence angle, the laser beam hits the target to form a small spot diameter, which makes the laser altimeter has a good horizontal resolution. If we obtain high-density detection points, we can get a more precise topographic map of the detection area.
U.S. scientists used this laser altimeter on the first and second generation Mars probes to obtain topographical maps of the Martian surface. A topographic map of the surface of Mars obtained by an altimeter measuring above the Martian equator. Scientists use different colors to calibrate different heights, and the topography of the surface of Mars is displayed in front of us in a simple and vivid way. This undoubtedly provides a powerful weapon for mankind to explore the universe, and also provides valuable information for the Mars rover to select the best landing site.
Usage in my country
Now, our aerospace scientists are working on the design and development of the first phase of the "Lunar 1" satellite. On the basis of in-depth analysis and research on the development of international lunar exploration and the results achieved, relevant experts combined with my country’s lunar exploration development plan and technical basis, and after sufficient demonstration, determined the science of the first phase of the "Tanyue No. 1" satellite And application goals. Among them, the laser altimeter will achieve the task of obtaining the altitude data of the moon's surface under the satellite, serving the scientific and application goals of obtaining three-dimensional images of the moon's surface. Measure the distance from the satellite to the sub-satellite point on the surface of the moon through the on-board laser altimeter, provide correction parameters for the stereo mapping of the optical imaging detection system; and use the ground application system to perform comprehensive data processing on the relationship between the distance data and the satellite orbit parameters and the earth-moon coordinates , Obtain the terrain height data of the satellite under-satellite point and moon table.
The working phases of the "Explore Moon 1" satellite are divided into the launch orbit phase, the transfer orbit phase and the lunar orbit phase. The laser altimeter does not work before entering the lunar orbit phase. After entering the lunar phase, the laser altimeter will operate for a long time regardless of whether the moon's surface is day or night, and whether the satellite is in a forward or side flight state. Therefore, the design of this laser altimeter should not only pay attention to the realization of parameter indexes, but also strive to improve its working stability and durability.
my country has included the second and third lunar exploration projects in my country’s mid- and long-term planning. The second phase of the lunar exploration project-"Moon Soft Landing and Lunar Rover Patrol Survey" will conduct a fine survey of the landing area. Lay a solid foundation for the third phase of the lunar exploration project-"Lunar rover inspection and sampling return", provide a scientific basis for the site selection of the lunar base, and accumulate experience and technology for manned lunar landing and the construction of the lunar base. In addition, my country has begun to demonstrate the exploration of Mars and asteroids, and the laser altimeter and related technologies will play a role in the above-mentioned engineering projects.