LIDAR, from past 4 to 5 days, we all are hearing about this technology in news just because two well-known companies one an IT-Giant – Google and other the fast-growing cab service – Uber are fighting over it. Well, I am not going into details of this feud, or anything like defending any of the company or any facts like which company invented this or patented this, how all this feud started etc. etc…
But surely this blog will give you some facts as some basics about LIDAR Technology and some present applications of this technology.
What is LIDAR Technology?
LIDAR, stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses – combined with other data recorded by the airborne system – generate precise, three-dimensional information about the shape of the target object and its surface characteristics.
LIDAR systems allow scientist and mapping professionals to examine both natural and manmade environments with accuracy, precision, and flexibility. NOAA scientists are using LIDAR to produce more accurate shoreline maps, make digital elevation models for use in geographic information systems, to assist in emergency response operations, and in many other applications.
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Types of LIDAR
With airborne LIDAR, the system is installed in either a fixed-wing aircraft or helicopter. The infrared laser light is emitted toward the ground and returned to the moving airborne LIDAR sensor. There are two types of airborne sensors:
- Topographic – Topographic LIDAR typically uses a near-infrared laser to map the land.
- Bathymetric – Bathymetric LIDAR uses water-penetrating green light to also measure seafloor and riverbed elevations.
Terrestrial LIDAR collects very dense and highly accurate points, which allows precise identification of objects. These dense point clouds can be used to manage facilities, conduct highway and rail surveys, and even create 3D city models for exterior and interior spaces. There are 2 main types of terrestrial LIDAR:
- Mobile – Mobile LIDAR is the collection of LIDAR point clouds from a moving platform. Mobile LIDAR systems can include any number of LIDAR sensors mounted on a moving vehicle.
- Static – Static LIDAR is the collection of LIDAR point clouds from a static location. Static LIDAR system is mounted on a tripod or stationery device which is portable, laser-based ranging and imaging system. These systems can collect LIDAR point clouds inside buildings as well as exteriors. Common applications for this type of LIDAR are engineering, mining, surveying, and archaeology.
How it works?
The principle of LIDAR is similar to Electronic Distance Measuring Instrument (EMI), where a laser (pulse or continuous wave) is fired from a transmitter and the reflected energy is captured. Using the time of travel of this laser the distance between the transmitter and reflector is determined. The reflector could be natural objects or an artificial reflector like prism.
The measurement can be simply explained with the following equation:
In other words LIDAR sensors work similar to radar technology, but instead of using radio waves, it uses laser light pulses that go as fast as 10,000 times per second. A pulse of light is emitted and the precise time of its emission is recorded. The reflection of that pulse is detected and the precise time of reception is recorded. Using the constant speed of light, the delay can be converted into a “slant range” distance. And the XYZ coordinate of the reflective surface can be calculated using the position and orientation of sensor as reference.
Listing below are the parts in an LIDAR System that work together to produce highly accurate, usable results:
- Laser – Lasers are categorized by their wavelength. Lasers with a wavelength of 1550nm are a common alternative as they are not focused by the eye and are ‘eye-safe’ at much higher power levels. These wavelengths are used for longer range and lower accuracy purposes. Another advantage of 1550nm wavelengths is that they do not show under night-vision goggles and are therefore well suited to military applications.
- LIDAR Sensors – It scans the ground from side to side as the plane flies. The sensor is commonly in green or near-infrared bands.
- Inertial Measurement Units – tracks the altitude and location of the airplane. These variables are important in attaining accurate terrain elevation values.
- Computers – it is used for Data storage and management systems which stores the data provided by the scan done by the system.
- Scanners and Optics – The speed at which images can be developed is affected by the speed at which it can be scanned into the system.
- Photo detector and Receiver electronics – Photo Detector is the device that reads and records the signal being returned to the system.
- High-precision clock – records the time the laser pulse leaves and returns to the scanner.
- Navigation and positioning systems – GPS receivers help track the altitude and location of the airplane. These variables are important in attaining accurate terrain elevation values.
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I hope that by now you would have got the idea of what LIDAR technology is and what is the purpose of using this technology. Waymo the self-driving car business of Google is using this technology in self-driven vehicles to help them scan and detect the obstacles on the road and with that some advanced software calculations give the results in the form of change in directions which the moving vehicles then executes. And if we talk of Uber, LIDAR technology is being used in their driverless cabs in order to increase their services for the people.
The method of detecting obstacles by sending the signals, receiving the reflection and then calculating the difference of time to know the position of the object is not completely new in the technology world. Neither the use of Laser lights in this method is new. What is new here is the use and development of this technique in order to use it for Self-driving vehicle mechanism.
In the next blog I would list some areas where this technology is being used and the purpose that is achieved by using LIDAR Technology.