Measuring Principle and Method of Using Laser to Measure the Distance from the Moon to the Earth
1. What is the principle of using infrared ranging or laser ranging? The principle of ranging can basically be attributed to measuring the time required for light to go back and forth to the target, and then calculate the distance D through the speed of light c = 299792458m/s and the atmospheric refraction coefficient n. Because it is difficult to measure time directly, it is usually to measure the phase of continuous wave, which is called phase measuring range finder. Of course, there are also pulse rangefinders, the typical one is WILD’s DI-3000. It should be noted that the phase measurement is not to measure the phase of infrared or laser, but to measure the phase of the signal modulated on infrared or laser. The construction industry has a handheld laser distance meter for house surveying that works on the same principle.
2. Must the plane of the measured object be perpendicular to the light? Usually precision distance measurement requires the cooperation of a total reflection prism, while the rangefinder used for house measurement directly measures with smooth wall reflection, mainly because the distance is relatively short and the signal strength of the light reflected back is large enough. It can be known from this that it must be vertical, otherwise the return signal is too weak and the accurate distance cannot be obtained.
3. Is it possible if the plane of the measured object is diffuse reflection? Usually it is also possible. In actual engineering, a thin plastic plate is used as a reflective surface to solve the serious problem of diffuse reflection.
4. The accuracy of ultrasonic ranging is relatively low, and it is rarely used now.
