Types Of LiDAR Technologies
Remote sensing, surveying, and monitoring have, in the last few years, reached new heights with the power of the LiDAR technology. LiDAR stands for Light Detection and Ranging, is a technique used to find range of a distant target using principles of light scattering. LiDAR systems are currently being used in various industries including forestry, disaster management, weather prediction, construction, archaeology, autonomous vehicles, etc. A wide variety of LiDAR technologies are available on the market today, and it is important to choose the appropriate one for successful usage. We will see in detail the two main types of LIDAR based on their functionality in this blog; which are — terrestrial and airborne.
Terrestrial LiDAR
Terrestrial LiDAR, as the name suggests, is a ground-based system. It can be installed on a moving vehicle or at a stationary position. Terrestrial LiDAR data is useful for applications that demand a detailed survey of the ground or a “closer look” at things in either case. Because this laser scanning device is frequently used in crowded settings with people, the lasers are normally eye-safe, posing no danger to anyone. Construction, self-driving vehicles, road surveys, city surveys, etc. are some of the applications of terrestrial LiDAR. Mobile and Static LiDAR are the 2 divisions of terrestrial LiDAR technologies.
Mobile
A sensor, a global positioning system (GPS), an inertial navigation system (INS), and a couple cameras make up a mobile LiDAR setup. The LiDAR unit is mounted on top of a moving vehicle and continues to shoot out laser pulses in all directions and read the reflections to obtain the data. The obtained point clouds (data points) are then analysed to determine the state of roads and railway tracks, as well as detect undesired road impediments. An advanced rotating LiDAR sensor installed on top of the car identifies the presence of pedestrians and other vehicles on the road in self-driving automobiles.
Static
In some applications, having the LiDAR unit stationary at one location rather of moving around is preferable. Static LiDAR is used in such applications. The LiDAR unit is mounted on a stationary object, which is commonly a tripod, in this setup. The complete apparatus, including the tripod, can be transferred to a new place if necessary. In essence, this unit is entirely portable, despite the fact that it is not mobile. From a fixed place, a static LiDAR unit continues to deliver laser pulses to the surrounding region. The information is then utilised to deduce the features of the environment. This feature is extremely useful in a variety of applications, including construction, mining, engineering, wind speed prediction, and so on.
Airborne LiDAR
When a LiDAR unit is airborne, it indicates the device is installed in an airplane or a helicopter that hovers above the earth’s surface, emitting laser pulses downward as it moves. Airborne LiDAR systems can scan for as long as the aircraft is in the air, giving you the ability to investigate miles and miles of land with no real-time constraints. As a result, for scanning projects spanning broad areas, this form of LiDAR is frequently the best solution. It can be more expensive to use an aircraft — especially a larger aircraft — than to use terrestrial LiDAR. Airborne LiDAR, on the other hand, may be more cost-effective for larger projects as more area can be covered in a short time period.
Airborne LiDAR can be further classified into 2 main types: topographic and bathymetric. While the functioning principle of both are similar, their working capacities differ.
Topographic
Topographic LiDAR systems scan surfaces, collecting elevation measurements to calculate how high above sea level different spots on the ground are. This laser scanning technique collects data for urban planning projects such as highway or railroad design, housing developments, and infrastructure. Topographic maps of the scanned area can be created using the point cloud data gathered from topographic LiDAR. Topographic maps use lines and colours to depict the surface contouring. They can show where land or man-made structures rise and fall to create an accurate landscape picture.
Bathymetric
While topographic LiDAR can detect any type of land from a distance, it struggles when scanning water features. Another sort of airborne LiDAR technology, known as bathymetric LiDAR, is employed to do this work. A bathymetric LiDAR sensor has all of the components of a topographic LiDAR with the addition of the ability to send green laser pulses. These pulses can pass through water and back to the airborne vehicle. The depth of the water bodies can be estimated using the data acquired in this manner. These units can more clearly identify shorelines and elevations when used in conjunction with topographic sensors. These LiDAR systems are commonly used in coastal engineering and marine sciences.
LiDAR devices can also be installed in spacecraft orbiting the planet. It is now possible to scan larger areas of the globe, as well as the airspace above it, using satellite LiDAR systems. NASA has deployed a variety of space-borne LiDAR systems to study cloud positions above the planet, vegetation, the state of the ice at the two poles, and other topics. More improved satellite LiDAR devices that can read particles in the atmosphere are being developed.
Although the underlying operating concept of most LiDAR systems is similar, particular applications demand the use of unique LiDAR units. Some types of LIDARs based on application include: Differential Absorption LiDAR (DIAL), Wind LiDAR, Raman LiDAR and High Spectral Resolution LiDAR (HSRL).
DIAL systems can be both terrestrial and airborne. The major applications of DIALs are measuring gas concentrations in the atmosphere and monitoring ozone levels. They can also determine the level of pollution. Measuring the flow of wind with any type of remote sensing technology can be difficult, partly because the wind changes direction quickly. Wind LiDAR was created specifically for this purpose. Water vapour and aerosol levels are detected and measured using Raman and HSR LiDARs. In contrast to terrestrial Raman systems, HSRLs are airborne.
Because LiDAR is still being effectively employed in a variety of applications, understanding the many forms of LiDAR gives consumers an advantage when choosing the proper system. LiDAR units are grouped into several different varieties based on their numerous functionalities, technology, setup, and applications. LiDAR units can be employed in a variety of ways, from the air to the ground, and from mobile to static. LiDAR has the potential to be employed in a wider range of applications in the future, thanks to advancements in technology such as differential absorption and inelastic scattering.