Principles and Characteristics of Laser Rangefinders
The principle of laser ranging or infrared ranging can basically be summarized as measuring the round-trip time of light traveling to the target. The distance D is then calculated using the speed of light c = 299792458 m/s and the atmospheric refractive index n. Since direct time measurement is difficult, the phase of continuous waves is usually measured; such instruments are known as phase-shift rangefinders. There are also pulse rangefinders, a typical example being the WILD DI-3000. It should be noted that phase measurement does not measure the phase of infrared or laser light itself, but the phase of the signal modulated onto the infrared or laser beam.
There is a handheld rangefinder for housing measurement in the construction industry, which operates on this same principle.
The plane of the measured object must be perpendicular to the light beam. High-precision ranging usually requires a total reflection prism. Rangefinders used for building measurement can perform measurements directly by reflection off smooth walls. This is mainly because the measurement distance is relatively short, and the reflected light signal has sufficient intensity. Therefore, the plane of the measured object must be perpendicular to the light beam; otherwise, the return signal will be too weak to obtain an accurate distance.
Is measurement feasible if the surface of the target object produces diffuse reflection? Generally, yes. In practical engineering, thin plastic boards are used as reflecting surfaces to solve severe diffuse reflection problems.
In practice, ultrasonic rangefinders have relatively low accuracy and often fail to meet user requirements during operation.
Brief knowledge about laser rangefinders A laser rangefinder is an instrument that accurately measures the distance to a target using laser light. During operation, it emits a thin laser beam toward the target. A photoelectric element receives the laser beam reflected by the target, and a timer measures the time taken for the laser beam from emission to reception to calculate the distance from the observer to the target.
If the laser is emitted continuously, the measuring range can reach approximately 40 kilometers, and operations can be carried out day and night. If the laser is emitted in pulses, the absolute accuracy is generally lower, yet it delivers good relative accuracy for long-distance measurement.
The world's first laser was successfully developed in 1960 by scientist Maiman from Hughes Aircraft Company in the United States. The US military quickly launched research on military laser devices based on this breakthrough. In 1961, the first military laser rangefinder passed US military verification tests. After that, laser rangefinders were rapidly put into practical service.
Laser rangefinders feature light weight, compact size, simple operation, fast measuring speed and high accuracy. Their measurement error is only 1/5 to 1/several hundred of that of other optical rangefinders. Therefore, they are widely used for topographic surveying, battlefield measurement, target ranging for tanks, aircraft, ships and artillery, as well as height measurement of cloud layers, aircraft, missiles and artificial satellites. They serve as key technical equipment for improving the firing accuracy of tanks, aircraft, ships and artillery.
