How Laser Ranging Works

According to the basic principle, there are two types of laser ranging methods: time-of-flight (TOF) ranging and non-time-of-flight ranging. There are pulsed laser ranging and phase-based laser ranging in time-of-flight ranging.

Pulse ranging is a measurement method that was first used in the field of surveying and mapping by laser technology. Because the laser divergence angle is small, the laser pulse duration is extremely short, and the instantaneous power is extremely large, so it can achieve extremely long range. In general, the cooperative target is not used, but the diffuse reflection of the light signal by the measured target is used to measure the distance.

The principle of the pulsed ranging method is well understood. A high-frequency clock drives the counter to count the time between sending and receiving pulses, which makes the period of the counting clock much smaller than the time between sending and receiving pulses to ensure Sufficient accuracy, so this ranging method is suitable for long-distance measurement.

The emission angle of pulsed laser is small, the energy is relatively concentrated in space, and the instantaneous power is large. Using these characteristics, various medium and long-distance laser rangefinders, lidars, etc. can be made. At present, pulsed laser ranging is widely used in topographic and geomorphological measurement, geological exploration, engineering construction measurement, aircraft height measurement, traffic and logistics obstacle avoidance, industrial distance measurement and other technical aspects.

Phase laser ranging is to use the frequency of the radio band to modulate the amplitude of the laser beam and measure the phase delay generated by the modulation light going back and forth to the measuring line, and then convert the distance represented by the phase delay according to the wavelength of the modulated light. That is, the time required for the light to travel back and forth through the survey line is measured by an indirect method. Phase laser ranging is generally used in the field of precision ranging. Due to its high accuracy, generally in the order of millimeters, in order to effectively reflect the signal and limit the measured target to a specific point commensurate with the accuracy of the instrument, this ranging device is equipped with a reflection called a cooperative target. plate.

Phase laser ranging is usually suitable for short- and medium-distance measurement, and the measurement accuracy can reach millimeters. It is also a method with the highest ranging accuracy at present. Phase ranging is to modulate the light intensity of the emitted light wave with a modulated signal, and indirectly measure the time by measuring the phase difference, which is much less difficult than directly measuring the round-trip time.

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