Principle of operation
A frequency-modulated RADIUS is projected onto a target. The target returns this RADIUS to the device. The time taken by the Department to return is measured and the distance between the user of the target is calculated.
A neighbour principle is used by security forces to carry out speed checks.
The speedometer is implementing the infrared radiation emitted by a laser pulse trains. When the beam encounters a target in motion (vehicle), a fraction of the beam is returned to the speedometer (reflective beam).
The measurement of the speed of the targeted vehicles is determined from the change in the interval between the pulses reflected by the vehicle. The vehicle moves away quickly, more time separating two successive reflected pulses increases (Doppler effect)\ [archive]
In the armed forces
Technology has allowed to develop systems to aid in the conduct of shooting with the development of laser rangefinder coupled to a ballistic computer whose purpose is to calculate the correction to apply to the angle and direction of the barrel depending on the distance ,
the direction and speed of the purpose, to the type of ammunition present in the cylinder head as a gun can fire several types of shells, speed and the direction of the tank shooter, the speed and the direction of the wind, etc. Simply send a signature laser on the target and shoot.
With this principle, we know the distance of the shot in the goal. Simply renew the process after a time given t and calculate the difference in the two time α1 and α2. The result is a time v which is nothing other than the time image of the distance travelled during a time given t.
With deducted information from the simple calculation of the distance from the time, we get the speed.
In the forest
In the forest, it is difficult to ensure that the RADIUS is well reflected by the desired target. An anti-feuille system with a special reflector is used. The laser beam is reflected on this reflector, which allows accurate measurements even in the undergrowth. This system is used for example in forest inventories.
Defects of the laser rangefinder
Problems due to the refraction of light when the ray passes through a plate of glass or plastic, or a cloud more or less in charge of water, or to differences in temperature of the water layers when you are in possession of a sonar or ASDIC, alter the data obtained. Visually, we dive a straight object in the water, it seems 'broken' at the place of separation between air and water.
This phenomenon is linked to the difference in speed of light (or used, sound or light wave) in the different strata through this RADIUS or wave. Thus, if the RADIUS crosses several layers (dry, wet, fog and smoke, for example) the assessment distance is unreliable.
In combat, a parade to the use of the laser rangefinder is of smoke grenades in the direction of the shooter, which makes its laser system inoperative. Either the shooter used the previously obtained data, reliability decreases with time (one or several parameters may change),.
He's waiting for the smoke to clear (to see the target hidden behind the curtain of smoke and/or be able to again use his rangefinder), risking a replica on the part of the opponent (who no longer sees his enemy), either happens rangefinder and eff made the elevation and the correction himself.
Electronic responses exist, to blur the received wave. They make the result totally implausible, and the shooter can understand that the target is trying to blur the wave.