Lasers can be used to determine the distance between objects for a variety of applications.
Laser distance measurement tools include a variety of devices. The technique ranges from shooting a short burst of concentrated light toward a target to units that use continuous beams. The devices have photodetectors that receive the reflected light from the targets. By using the speed of light and the time taken for the lasers to travel to and from the targets, you can determine the distance.
Pulsed Time-of-Flight Method
The transmitter and photodetector used in this method are both optical systems. The detector serves as an antenna for the device. The device uses a short duration burst and high-peak power. Common applications include military range-finding, missile tracking and rocket tracking. Mathematical formulas take geometrical factors such as detector sensitivity, transmitter power and antenna size into account as they affect the difference between transmitted and received power. The effects of atmosphere upon beam density is factored in, as is diffusion of light by different types of targets.
Noncooperative and Cooperative Targets
A noncooperative target is considered to be an object that defuses the laser. Examples of this could include a tree, building or rock. The term noncooperative is used to indicate that the object has not been prepared to enhance the beam. A cooperative object has had its reflectivity enhanced to return a stronger signal. An example of this would be a cube corner reflector. This device is usually a prism in the shape of pyramid that allows internal reflection of the beam. This enables the reflected beam to be parallel with the projected beam for accurate measurement.
Beam Modulation Telemetry
This device uses a continuous wave laser. The method measures the time between the transmission of the beam at a given sine of the light wave and the receiving beam at the sine wave length. The more accurate models of this device use several frequencies of the beam modulation. Lower frequencies prevent ambiguous range measurement. Higher frequencies provide greater accuracy. The accuracy of this technique is affected by signal strength and noise. Turbulence in the air and variations in refraction will also affect accuracy. The method is primarily used in land surveying and land profiling.
Interferometric Methods
Interferometric measurement uses inference to provide highly accurate distance measurements. The technique relies upon the inferred spectrum of a given wavelength of a beam being transmitted. The beam is split into two at the transmitter and reflected off of two mirrors. One beam serves as a reference and the other as a measurement. The variation between the two beams can be measured and a precise distance determined by a photoreceptor or observer. This technique is suitable for controlled atmospheres and shorter distances.
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