A laser rangefinder, also known as a laser telemeter, is a
rangefinder
A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in surveying, they soon found applications in other fields, such as photography an ...
that uses a
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
beam to determine the
distance
Distance is a numerical or occasionally qualitative measurement of how far apart objects or points are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two counties over"). ...
to an object. The most common form of laser rangefinder operates on the
time of flight
Time of flight (ToF) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a w ...
principle by sending a laser pulse in a narrow beam towards the object and measuring the
time
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...
taken by the pulse to be reflected off the target and returned to the sender. Due to the high
speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
, this technique is not appropriate for high precision sub-millimeter measurements, where
triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points.
Applications
In surveying
Specifically in surveying, triangulation involves only angle me ...
and other techniques are often used.
Pulse
The pulse may be coded to reduce the chance that the rangefinder can be
jammed. It is possible to use
Doppler effect
The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...
techniques to judge whether the object is moving towards or away from the rangefinder, and if so, how fast.
Precision
The precision of the instrument is determined by the
rise or fall time of the laser pulse and the speed of the receiver. One that uses very sharp laser pulses and has a very fast detector can range an object to within a few millimeters.
Range and range error
Despite the
beam
Beam may refer to:
Streams of particles or energy
*Light beam, or beam of light, a directional projection of light energy
**Laser beam
*Particle beam, a stream of charged or neutral particles
**Charged particle beam, a spatially localized grou ...
being narrow, it will eventually spread over long distances due to the
divergence
In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the quantity of the vector field's source at each point. More technically, the divergence represents the volume density of the ...
of the laser beam, as well as due to scintillation and beam wander effects, caused by the presence of air bubbles in the air acting as lenses ranging in size from microscopic to roughly half the height of the laser beam's path above the earth.
These atmospheric
distortions
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signa ...
coupled with the divergence of the laser itself and with
transverse wind
A crosswind is any wind that has a perpendicular component to the line or direction of travel. This affects the aerodynamics of many forms of transport. Moving non-parallel to the wind's direction creates a crosswind component on the object and th ...
s that serve to push the
atmospheric
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
heat bubbles laterally may combine to make it difficult to get an accurate reading of the distance of an object, say, beneath some trees or behind bushes, or even over long distances of more than 1 km in open and unobscured desert terrain.
Some of the laser light might reflect off leaves or branches which are closer than the object, giving an early return and a reading which is too low. Alternatively, over distances longer than 1200 ft (365 m), the target, if in proximity to the earth, may simply vanish into a
mirage
A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', meanin ...
, caused by temperature
gradients
In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...
in the air in proximity to the heated surface bending the laser light. All these effects have to be taken into account.
Calculation
![20200501 Time of flight](https://upload.wikimedia.org/wikipedia/commons/f/f1/20200501_Time_of_flight.svg)
The distance between point A and B is given by
:
where
c is the speed of light and
t is the amount of time for the round-trip between A and B.
:
where
φ is the phase delay made by the light traveling and
ω is the angular frequency of optical wave.
Then substituting the values in the equation,
:
In this equation,
λ is the wavelength ;
Δφ is the part of the phase delay that does not fulfill (that is,
φ modulo );
N is the integer number of wave half-cycles of the round-trip and Δ
N the remaining fractional part.
Technologies
Time of flight
Time of flight (ToF) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a w ...
- this measures the time taken for a light pulse to travel to the target and back. With the speed of light known, and an accurate measurement of the time taken, the distance can be calculated. Many pulses are fired sequentially and the average response is most commonly used. This technique requires very accurate sub-
nanosecond
A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or 10 seconds.
The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit ( ...
timing circuitry.
Multiple frequency phase-shift - this measures the phase shift of multiple frequencies on reflection then solves some
simultaneous equations
In mathematics, a set of simultaneous equations, also known as a system of equations or an equation system, is a finite set of equations for which common solutions are sought. An equation system is usually classified in the same manner as single e ...
to give a final measure.
Interferometry
Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...
- the most accurate and most useful technique for measuring changes in distance rather than absolute distances.
Light attenuation by atmospheric absorption - The method measures the attenuation of a laser beam caused by the absorption from an
atmospheric compound (
H2O,
CO2,
CH4,
O2 etc.) to calculate the distance to an object. The light atmospheric absorption attenuation method requires unmodulated incoherent light sources and low-frequency electronics that reduce the complexity of the devices. Due to this, low-cost light sources can be used for range-finding. However, the application of the method is limited to atmospheric measurements or planetary exploration.
Applications
Military
Rangefinders
A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in surveying, they soon found applications in other fields, such as photography an ...
provide an exact distance to targets located beyond the distance of
point-blank
Point-blank range is any distance over which a certain firearm can hit a target without the need to compensate for bullet drop, and can be adjusted over a wide range of distances by sighting in the firearm. If the bullet leaves the barrel paral ...
shooting to snipers and artillery. They can also be used for military reconnaissance and engineering.
Handheld military rangefinders operate at ranges of 2 km up to 25 km and are combined with
binoculars
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...
or
monocular
A monocular is a compact refracting telescope used to magnify images of distant objects, typically using an optical prism to ensure an erect image, instead of using relay lenses like most telescopic sights. The volume and weight of a monocul ...
s. When the rangefinder is equipped with a digital magnetic compass (DMC) and inclinometer it is capable of providing magnetic azimuth, inclination, and height (length) of targets. Some rangefinders can also measure a target's speed in relation to the observer. Some rangefinders have cable or wireless interfaces to enable them to transfer their measurement(s) data to other equipment like fire control computers. Some models also offer the possibility to use add-on
night vision
Night vision is the ability to see in low-light conditions, either naturally with scotopic vision or through a night-vision device. Night vision requires both sufficient spectral range and sufficient intensity range. Humans have poor night vi ...
modules. Most handheld rangefinders use standard or rechargeable batteries.
The more powerful models of rangefinders measure distance up to 25 km and are normally installed either on a tripod or directly on a vehicle or gun platform. In the latter case the rangefinder module is integrated with on-board thermal, night vision and daytime observation equipment. The most advanced military rangefinders can be integrated with computers.
To make laser rangefinders and
laser-guided
Laser guidance directs a robotics system to a target position by means of a laser beam. The laser guidance of a robot is accomplished by projecting a laser light, image processing and communication to improve the accuracy of guidance. The key ide ...
weapons less useful against military targets, various military arms may have developed laser-absorbing paint for their vehicles. Regardless, some objects don't reflect laser light very well and using a laser rangefinder on them is difficult.
The first commercial laser rangefinder was the
Barr & Stroud
Barr & Stroud Limited was a pioneering Glasgow optical engineering firm. They played a leading role in the development of modern optics, including rangefinders, for the Royal Navy and for other branches of British Armed Forces during the 20th ce ...
LF1, developed in association with
Hughes Aircraft
The Hughes Aircraft Company was a major American aerospace and defense contractor founded on February 14, 1934 by Howard Hughes
Howard Robard Hughes Jr. (December 24, 1905 – April 5, 1976) was an American business magnate, record-setting p ...
, which became available in 1965. This was then followed by the Barr & Stroud LF2, which integrated the rangefinder into a tank sight, and this was used on the
Chieftain tank
The FV4201 Chieftain was the main battle tank of the United Kingdom during the 1960s–1990s.
A development of the Centurion, the Chieftain introduced the supine (reclining) driver position to British design allowing a heavily sloped hull with r ...
in 1969, the first vehicle so-equipped with such a system. Both systems used
ruby
A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sa ...
lasers.
3-D modeling
Laser rangefinders are used extensively in
3-D object recognition, 3-D object modelling, and a wide variety of
computer vision
Computer vision is an interdisciplinary scientific field that deals with how computers can gain high-level understanding from digital images or videos. From the perspective of engineering, it seeks to understand and automate tasks that the hum ...
-related fields. This technology constitutes the heart of the so-called ''time-of-flight''
3D scanner
3D scanning is the process of analyzing a real-world object or environment to collect data on its shape and possibly its appearance (e.g. color). The collected data can then be used to construct digital 3D modelling, 3D models.
A 3D scanner can ...
s. In contrast to the military instruments described above, laser rangefinders offer high-precision scanning abilities, with either single-face or 360-degree scanning modes.
A number of algorithms have been developed to merge the range data retrieved from multiple angles of a single object to produce complete 3-D models with as little error as possible. One of the advantages that laser rangefinders offer over other methods of computer vision is that the computer does not need to correlate features from two images to determine depth information as in
stereoscopic
Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the depth perception, illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stere ...
methods.
Laser rangefinders used in computer vision applications often have depth resolutions of tenths of millimeters or less. This can be achieved by using triangulation or refraction measurement techniques as opposed to the time of flight techniques used in
LIDAR
Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
.
Forestry
![Field-Map birdie](https://upload.wikimedia.org/wikipedia/commons/8/80/Field-Map_birdie.jpg)
Special laser rangefinders are used in
forestry
Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forests, woodlands, and associated resources for human and environmental benefits. Forestry is practiced in plantations and natural stands. Th ...
. These devices have anti-leaf filters and work with
reflector
Reflector may refer to:
Science
* Reflector, a device that causes reflection (for example, a mirror or a retroreflector)
* Reflector (photography), used to control lighting contrast
* Reflecting telescope
* Reflector (antenna), the part of an ant ...
s. Laser beam reflects only from this reflector and so exact distance measurement is guaranteed. Laser rangefinders with anti-leaf filter are used for example for
forest inventories.
Sports
Laser rangefinders may be effectively used in various sports that require precision distance measurement, such as
golf
Golf is a club-and-ball sport in which players use various clubs to hit balls into a series of holes on a course in as few strokes as possible.
Golf, unlike most ball games, cannot and does not use a standardized playing area, and coping wi ...
,
hunting
Hunting is the human activity, human practice of seeking, pursuing, capturing, or killing wildlife or feral animals. The most common reasons for humans to hunt are to harvest food (i.e. meat) and useful animal products (fur/hide (skin), hide, ...
, and
archery
Archery is the sport, practice, or skill of using a bow to shoot arrows.Paterson ''Encyclopaedia of Archery'' p. 17 The word comes from the Latin ''arcus'', meaning bow. Historically, archery has been used for hunting and combat. In m ...
. Some of the more popular manufacturers are Caddytalk, Opti-logic Corporation, Bushnell, Leupold, LaserTechnology, Trimble, Leica, Newcon Optik, Op. Electronics,
Nikon
(, ; ), also known just as Nikon, is a Japanese multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging products. The companies held by Nikon form the Nikon Group.
Nikon's products include cameras, camera ...
, Swarovski Optik and
Zeiss Zeiss or Zeiß may refer to:
People
*Carl Zeiss (1816–1888), German optician and entrepreneur
*Emil Zeiß (1833–1910), German Protestant minister and painter
Companies
*Carl Zeiss AG, German manufacturer of optics, industrial measurem ...
.
Many rangefinders from Bushnell come with advanced features, such as ARC (angle range compensation), multi-distance ability, slope, JOLT (Vibrate when the target is locked), and Pin-Seeking. ARC can be calculated by hand using the
rifleman's rule
Rifleman's rule is a "rule of thumb" that allows a rifleman to accurately fire a rifle that has been calibrated for horizontal targets at uphill or downhill targets. The rule says that only the horizontal range should be considered when adjusting ...
, but it's usually much easier if you let a rangefinder do it when you are out hunting. In golfing where time is most important, a laser rangefinder comes useful in locating distance to the flag. However not all features are 100% legal for golf tournament play. Many hunters in the eastern U.S. don't need a rangefinder, although many western hunters need them, due to longer shooting distances and more open spaces.
Industrial production processes
An important application is the use of laser rangefinder technology during the automation of stock management systems and production processes in steel industry.
Laser measuring tools
![Bosch GLM 50 C](https://upload.wikimedia.org/wikipedia/commons/7/7a/Bosch_GLM_50_C.jpg)
Laser rangefinders are also used in several industries like construction, renovation and real estate as an alternative to a
tape measure
A tape measure or measuring tape is a flexible ruler used to measure length or distance.
It consists of a ribbon of cloth, plastic, fibre glass, or metal strip with linear measurement markings. It is a common measuring tool. Its design all ...
, and was first introduced by
Leica Geosystems
Leica Geosystems (formerly known as Wild Heerbrugg or just Wild) based in eastern Switzerland produces products and systems for surveying and geographical measurement (geomatics). Its products employ a variety of technologies including GPS sat ...
in 1993 in
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
. To measure a large object like a room with a tape measure, one would need another person to hold the tape at the far wall and a clear line straight across the room to stretch the tape. With a laser measuring tool, the job can be completed by one operator with just a line of sight. Although the tape measure is typically more accurate, laser measuring tools can be calibrated to be generally reliable when taking several measurements. Laser measuring tools typically include the ability to produce some simple calculations, such as the
area
Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape
A shape or figure is a graphics, graphical representation of an obje ...
or
volume
Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...
of a room, as well as switch between imperial and metric units. These devices can be found in hardware stores and online marketplaces.
Price
Laser rangefinders can vary in price, depending on the quality and application of the product. Military grade rangefinders need to be as accurate as possible and must also reach great distances. These devices can cost hundreds of thousands of dollars. For civilian applications, such as hunting or golf, devices are more affordable and much more readily accessible.
Safety
Laser rangefinders are divided into four classes and several subclasses. Laser rangefinders available to consumers are usually laser
class 1 or
class 2 devices and are considered relatively eye-safe.
Regardless of the safety rating, direct eye contact should always be avoided. Most laser rangefinders for military use exceed the laser class 2 energy levels.
See also
*
Geodimeter __NOTOC__
The Geodimeter (acronym of geodetic distance meter) was the first optical electronic distance meter surveying instrument.
It was originally developed for measuring the speed of light.
It was invented in 1947 by and commercialized in 195 ...
*
Laser altimetry
Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranging, ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can ...
*
Laser designator
A laser designator is a laser light source which is used to designate a target. Laser designators provide targeting for laser-guided bombs, missiles, or precision artillery munitions, such as the Paveway series of bombs, AGM-114 Hellfire, or ...
*
Laser machine control
*
Laser scanning
Laser scanning is the controlled deflection of laser beams, visible or invisible.
Scanned laser beams are used in some 3-D printers, in rapid prototyping, in machines for material processing, in laser engraving machines, in ophthalmological la ...
*
Laser warning receiver
A laser warning receiver is a type of warning system used as a passive military defence. It detects, analyzes, and locates directions of laser emissionsPDF version4.53 MB) from laser guidance systems and laser rangefinders. Then it alerts the cre ...
*
List of laser articles
This is a list of laser topics.
A
* 3D printing, additive manufacturing
* Abnormal reflection
* Above-threshold ionization
* Absorption spectroscopy
* Accelerator physics
* Acoustic microscopy
* Acousto-optic deflector
* Acousto-optic modul ...
*
Range imaging
Range imaging is the name for a collection of techniques that are used to produce a 2D image showing the distance to points in a scene from a specific point, normally associated with some type of sensor device.
The resulting range image has pix ...
*
Satellite laser ranging
In satellite laser ranging (SLR) a global network of observation stations measures the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors. This provides instantaneous range measurements of milli ...
References
External links
A brief write-up on Hunting Rangefinder and its types.
{{DEFAULTSORT:Laser Rangefinder
Length, distance, or range measuring devices
Laser applications
Forestry tools
Surveying instruments