What is a Laser?
Laser-based tools help us do all sorts of things these days, but what exactly is a laser? Laying aside the fact that the word itself stands for Light Amplification by Stimulated Emission of Radiation-in other words, an acronym-this particular form of light has the ability to be focused in a very narrow manner. Take the ordinary flashlight. The beam broadens very quickly when you switch it on. This is because the electromagnetic waves that make up the complete light spectrum are of many different wavelengths. With the laser, the waves are taken from very specific wavelengths that make them almost all parallel to each other. This means there is very little “scatter.” A laser beam that is only six to ten millimeters in diameter at its source may only be slightly larger than a centimeter in diameter, when projected on an object as far as a kilometer away!
Using Lasers for Measurement
Because of this unique aspect of the laser, devices can be built that offer extremely precise measurement capabilities. In this respect, the laser operates much the same way radar works. In radar, sound waves are thrown at a target. They bounce off, and some portion returns to the source. Calculations are made, and it can therefore be determined how far away an object may be (or how fast it is traveling) based upon the time it takes for the sound waves to go out and return. For lasers, the light beam is switched on, or else it is pulsed multiple times. As the beam travels through the air, it reflects off the target surface and then bounces back to the device. One of the advantages of laser over radar is volume. Sound waves are prone to scatter the same way the illumination from your flashlight brightens an entire room. Only a portion of the radar waves returns to the sensor. For laser devices, the rate of return is incredibly high. As a result, it is possible to generate extremely precise measurements unlike with any other method.
How Does a Laser Scanner Work?
Laser-based measuring devices, no matter what their particular application, all work pretty much the same way. The element that generates the laser beam is designed to shoot out light waves at an amazing rate. Some products can generate up to 750,000 pulses per second, although the average is around 10,000 per second. The resulting data that is collected by the sensor, as these millions of beams are reflected back to the device, generate something called a “point cloud.” This is a highly descriptive term, if you think if the millions of water droplets it takes to make up the three-dimensional aspects of a cloud one sees in the sky. Through manipulation and extrapolation by employing various software programs designed to interpret laser point clouds, it is possible to create a 3D picture of the surface one is observing.
The Laser in a Surveying Application
The range finder is one of the primary laser-based devices available to the surveyor. Because surveyors are greatly interested in how far something is from something else, the laser is a great tool to employ in this manner. Three-dimensional laser scanning allows a surveyor to re-create the surface of an object-a building or a fence-or a natural feature, such as a rock face or a stand of trees. The surveyor will choose the specific tool he or she uses based upon the target and the desired results. A time-of-flight range finder can operate over great distances, perhaps as far as a few or a dozen kilometers. This unit is terrific for scanning buildings and large geological features, but one will sacrifice accuracy for distance. To the layman, if something is off a millimeter or two, that hardly seems tragic. And any surveyor using this particular model is well aware of its limitations. On the other hand, a triangulation range finder-so named because a triangle is formed that includes the laser dot, the laser receptor, and a camera mounted slightly off-center. Here one can achieve accuracy down in the ten-micrometer range, but a triangulation range finder is rarely useful beyond a distance of just a few meters from the object it is scanning.
Land Surveys Pty Ltd are a Perth surveying company providing all types of surveying services in Western Australia.
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