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1、Laser rangefinder A long range laser rangefinder is capable of measuring distance up to 20 km; mounted on a tripod with an angular mount. The resulting system also provides azimuth and elevation measurements. A laser rangefinder is a device which uses a laser beam to determine the distance to an obj
2、ect. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender. Due to the high speed of light, this technique is
3、not appropriate for high precision sub-millimeter measurements, where triangulation 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 techniques to judge whether the object is moving towards
4、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
5、 Despite the beam being narrow, it will eventually spread over long distances due to the divergence 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 heigh
6、t of the laser beams path above the earth.These atmospheric distortions coupled with the divergence of the laser itself and with transverse winds that serve to push the atmospheric heat bubbles laterally may combine to make it difficult to get an accurate reading of the distance of an object, say, b
7、eneath 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
8、 longer than 1200 ft (365 m), the target, if in proximity to the earth, may simply vanish into a mirage, caused by temperature gradients in the air in proximity to the heated surface bending the laser light. All these effects have to be taken into account.Calculation The distance between point A and
9、 B is given byD=ct/2where c is the speed of light in the atmosphere and t is the amount of time for the round-trip between A and B.where is the delay which made by the light traveling and is the angular frequency of optical modulation.Then substitute the values in the equation D=ct/2,D=1/2 ct=1/2 c/
10、=c/(4f) (N+)=c/4f (N+N)=U(N+)in this equation, U stands for the unit length. stands for the delay part which does not fulfill .N stands the decimal value.Discrimination Some instruments are able to determine multiple returns, as above. These instruments use waveform-resolving detectors, which means
11、they detect the amount of light returned over a certain time, usually very short. The waveform from a laser pulse that hits a tree and then the ground would have two peaks. The first peak would be the distance to the tree, and the second would be the distance to the ground.Using wavefront sensing, i
12、t is possible to determine both the closest and the farthest object at a given point. This makes it possible for aircraft-mounted instruments to see through dense canopiesclarification needed Please explain how lasers see through canopies and other semi-reflective surface such as the ocean, leading
13、to many applications for airborne instruments such as: 1. Creating bare earth topographic maps - removing all trees 2. Creating vegetation thickness maps 3. Bathymetry(measuring topography under the ocean) 4. Forest firehazard Technologies Time of flight - this measures the time taken for a light pu
14、lse 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 timing circuitry
15、. Multiple frequency phase-shift - this measures the phase shift of multiple frequencies on reflection then solves some simultaneous equations to give a final measure.Interferometry - the most accurate and most useful technique for measuring changes in distance rather than absolute distances.Applica
16、tionsMilitaryAn American soldier with a GVS-5 laser rangefinder. A Dutch ISAF sniper team displaying their Accuracy International AWSM .338 Lapua Magnum rifle and Leica/Vectronix VECTOR IV laser rangefinder binoculars.Rangefinders provide an exact distance to targets located beyond the distance of p
17、oint-blank shooting to snipers and artillery. They can also be used for military reconciliation and engineering. Handheld military rangefinders operate at ranges of 2 km up to 25 km and are combined with binoculars or monoculars. When the rangefinder is equipped with a digital magnetic compass (DMC)
18、 and inclinometer it is capable of providing magnetic azimuth, inclination, and height (length) of targets. Some rangefinders can also measure a targets speed in relation to the observer. Some rangefinders have cable or wireless interfaces to enable them to transfer their measurement(s) data to othe
19、r equipment like fire control computers. Some models also offer the possibility to use add-on night vision 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 o
20、r 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 weapons less u
21、seful against military targets, various military arms may have developed laser-absorbing paint for their vehicles. Regardless, some objects dont reflect laser light very well and using a laser rangefinder on them is difficult. 3-D Modelling This LIDAR scanner may be used to scan buildings, rock form
22、ations, etc., to produce a 3D model. The LIDAR can aim its laser beam in a wide range: its head rotates horizontally, a mirror flips vertically. The laser beam is used to measure the distance to the first object on its path. Laser rangefinders are used extensively in 3-D object recognition, 3-D obje
23、ct modelling, and a wide variety of computer vision-related fields. This technology constitutes the heart of the so-called time-of-flight 3D scanners. In contrast to the military instruments described above, laser rangefinders offer high-precision scanning abilities, with either single-face or 360-d
24、egree 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 tha
25、t the computer does not need to correlate features from two images to determine depth information as in stereoscopic 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 refracti
26、on measurement techniques as opposed to the time of flight techniques used in LIDAR. Forestry Laser rangefinder TruPulse used for forest inventories (in combination with Field-Map technology) Special laser rangefinders are used in forestry. These devices have anti-leaf filters and work with reflecto
27、rs. 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
28、 as golf, hunting, and archery. Some of the more popular manufacturers are: Opti-logic Corporation, Bushnell, LaserTechnology, Trimble, Leica, Newcon Optik, Nikon, and Swarovski Optik.Industry production processes An important application is the use of laser Range finder technology during the automa
29、tion of stock management systems and production processes in steel industry.Safety Laser rangefinders for consumers are laser class 1 devices and therefore are considered eyesafe. Some laser rangefinders for military use exceed the laser class 1 energy levels. History Development of the methods used
30、 in modern printed circuit boards started early in the 20th century. In 1903, a German inventor, Albert Hanson, described flat foil conductors laminated to an insulating board, in multiple layers. Thomas Edison experimented with chemical methods of plating conductors onto linen paper in 1904. Arthur
31、 Berry in 1913 patented a print-and-etch method in Britain, and in the United States Max Schoop obtained a patent1 to flame-spray metal onto a board through a patterned mask. Charles Durcase in 1927 patented a method of electroplating circuit patterns. The Austrian Jewish engineer Paul Eisler invent
32、ed the printed circuit while working in England around 1936 as part of a radio set. Around 1943 the USA began to use the technology on a large scale to make proximity fuses for use in World War II . After the war, in 1948, the USA released the invention for commercial use. Printed circuits did not b
33、ecome commonplace in consumer electronics until the mid-1950s, after the Auto-Sembly process was developed by the United States Army. Before printed circuits (and for a while after their invention), point-to-point construction was used. For prototypes, or small production runs, wire wrap or turret b
34、oard can be more efficient. Predating the printed circuit invention, and similar in spirit, was John Sargroves 19361947 Electronic Circuit Making Equipment (ECME) which sprayed metal onto a Bakelite plastic board. The ECME could produce 3 radios per minute. During World War II, the development of th
35、e anti-aircraft proximity fuse required an electronic circuit that could withstand being fired from a gun, and could be produced in quantity. The Centralab Division of Globe Union submitted a proposal which met the requirements: a ceramic plate would be screenprinted with metallic paint for conducto
36、rs and carbon material for resistors, with ceramic disc capacitors and subminiature vacuum tubes soldered in place. Originally, every electronic component had wire leads, and the PCB had holes drilled for each wire of each component. The components leads were then passed through the holes and solder
37、ed to the PCB trace. This method of assembly is called through-hole construction. In 1949, Moe Abramson and Stanislaus F. Danko of the United States Army Signal Corps developed the Auto-Sembly process in which component leads were inserted into a copper foil interconnection pattern and dip soldered.
38、 The patent they obtained in 1956 was assigned to the U.S. Army. 4 With the development of board lamination and etching techniques, this concept evolved into the standard printed circuit board fabrication process in use today. Soldering could be done automatically by passing the board over a ripple,
39、 or wave, of molten solder in a wave-soldering machine. However, the wires and holes are wasteful since drilling holes is expensive and the protruding wires are merely cut off. In recent years, the use of surface mount parts has gained popularity as the demand for smaller electronics packaging and g
40、reater functionality has grown.References1 M. Samules, S. Patterson, J. Eppstein, R. Fowler, Low cost handheld lidar system for automotive speed detection and law enforcement, Proc. SPIE 1633 (1992) 147159. 2 Z.X. Jia, K. Gong, Y.J. Huo, Optoelectronic system for high-speed flier velocity measuremen
41、t based on laser scattering, Opt. Eng. 48 (2009) 043601.3 H. Surmann, A. Nuchter, J. Hertzberg, An autonomous mobile robot with a 3D laser range finder for 3D exploration and digitalization of indoor environments, Robot. Auton. Syst. 45 (2003) 181198. 4 V. Sequeiraa, J. Goncalves, M. Ribeiro, 3D env
42、ironment modelling using laser range sensing, Robot. Autom. 16 (1995) 8191.5 K. Mdtta, J. Kostamovaara, R. Myllyla, Profiling of hot surfaces by pulsed time -of- flight laser range finder techniques, Appl. Opt. 32 (1993) 53345347.6 M.C. Amann, T. Bosch, M. Lescure, R. Myllyla, Laser ranging: a criti
43、cal review of usual techniques for distance measurement, Opt. Eng. 40 (2001) 1019.7 T. Ruotsalainen, P. Palojarvi, J. Kostamovaara, A wide dynamic range receiver channel for a pulsed time-of-flight laser radar, IEEE J. Solid-State Circuits 36 (2001) 12281238.8 S. Kurtti, J. Kostamovaara, An integrat
44、ed optical receiver with wide-range timing discrimination characteristics, in: Proceedings 31st European Solid- State Circuits Conference, Grenoble, France, 2005, pp. 435438.9 J. Nissinen, I. Nissinen, J. Kostamovaara, Integrated receiver including both receiver channel and TDC for a pulsed time-of-
45、flight laser rangefinder with cmlevel accuracy, IEEE J. Solid-State Circuits 44 (2009) 14861497.10 W.M.C. Sansen, R.G. Meyer, An integrated wide-band variable-gain amplifier with maximum dynamic range, IEEE J. Solid-State Circuits 9 (1974) 159166.11 H. Ikeda, T. Ohshima, M. Tsunotani, T. Ichioka, T.
46、 KimuraA, An auto-gain control transimpedance amplifier with low noise and wide input dynamic range for 10-Gb/s optical communication systems, IEEE J. Solid-State Circuits 36 (2001) 13031308.12 S. Yamashita, S. Ide, K. Mori, A. Hayakawa, N. Ueno, K. Tanaka, Novel cell-AGC technique for burst-mode CM
47、OS preamplifier with wide dynamic range and high sensitivity for ATM-PON system, IEEE J. Solid-State Circuits 37 (2002) 881C886.13 J. Nissinen, J. Kostamovaara, Laser pulser for a time-of-flight laser radar, Rev. Sci. Instrum. 68 (1997) 22532258. 激光测距仪 长距离激光测距仪测量距离可达20公里，安装在同一个角度或安装在三脚架上，所形成的系统也可测量方
48、位角和仰角测量。激光测距仪是一种设备，它采用了激光束来确定对象的距离。激光测距仪的最常见的运行方式是：将激光脉冲发送到要测量的对象，通过得到激光光束反射给激光脉冲发送者的时间来确定测量对象的距离。由于光的速度很高，这种技术拥有亚毫米级的高测量精度，在一些三角测量技术和其他技术中经常被。脉冲： 编码脉冲可减少测距仪失效的几率。这是使用多普勒效应的技术，来判断该对象是否是朝向或远离测距仪，因此，工作速度是十分快的。精度： 该仪器的精度是由激光脉冲的上升或下降时间和接收器的速度决定的。 一方面使用幅值非常高的激光脉冲，并有一个反映非常快的探测器，因此精度范围在几毫米之内。范围： 尽管是窄的光束 ，由于激光束的发散它传播的距离会很长，以及因空气中的气泡所引起的闪烁和光束漂移的影响，激光束的路径微观到地球上空大约一半的高度。 这些大气中的折射与激光本身的发散，再加上大气的热气泡横向相结合，使其很难获得一个距离的准确的读数，另外，在一些树木或灌木丛背后，甚至在视野开阔的沙漠地形中超过1公里长的距离也可能无法获得准确的数据。 一些激光测量的数据反映的可能会是树叶或树枝，这些干扰对象比测量对象密度更大，从而使反射回来的时间更短和数据的可读性太低。另外，距离超过1200英尺（365米），如果在接近地球的目标，不再只是可能到由温度引起的误差，还存在弯曲的激光加热表面附近的
