IS LiDAR Technology all we need in the future?
LIDAR technology (sometimes also written as “LiDAR“, “Lidar“, or “LADAR“) which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges to the Earth.
It is now also used as an acronym of “light detection and ranging” and “laser imaging, detection, and ranging”. LiDAR technology sometimes is called 3-D laser scanning, a special combination of a 3-D scanning and laser scanning.
A LiDAR instrument principally consists of a laser, a scanner, and a specialized GPS receiver. Airplanes and helicopters are the most commonly used platforms for acquiring lidar data over broad areas. Two types of LiDAR are topographic and bathymetric.
A point cloud generated from a moving car using a single Ouster OS1 lidar.
How is lidar data collected?
When an airborne laser is pointed at a targeted area on the ground, the beam of light is reflected by the surface it encounters. A sensor records this reflected light to measure a range.
When laser ranges are combined with position and orientation data generated from integrated GPS and Inertial Measurement Unit systems, scan angles, and calibration data, the result is a dense, detail-rich group of elevation points, called a “point cloud.”
Each point in the point cloud has three-dimensional spatial coordinates (latitude, longitude, and height) that correspond to a particular point on the Earth’s surface from which a laser pulse was reflected.
The point clouds are used to generate other geospatial products, such as digital elevation models, canopy models, building models, and contours.
To know more about what is LiDAR technology used for scroll below.
(Image source: National ocean service)
An animated visual on LIDAR showing how the laser works to collect data.
600–1000 nm lasers are most common for non-scientific applications. The maximum power of the laser is limited, or an automatic shut off system which turns the laser off at specific altitudes is used in order to make it eye-safe for the people in the ground.
Flash LIDAR allows for 3-D imaging because of the camera’s ability to emit a larger flash and sense the spatial relationships and dimensions of the area of interest with the returned energy.
This allows for more accurate imaging because the captured frames do not need to be stitched together, and the system is not sensitive to platform motion resulting in less distortion.
A phased array can illuminate any direction by using a microscopic array of individual antennas. Controlling the timing (phase) of each antenna steers a cohesive signal in a specific direction.
Phased arrays have been used in radar since the 1950s. The same technique can be used with light. On the order of a million optical antennas are used to see a radiation pattern of a certain size in a certain direction.
The system is controlled by timing the precise flash. A single chip (or a few) replace a $75,000 electromechanical system, drastically reducing costs.
Sensor and its use on smartphone:
Lidar uses active sensors that supply their own illumination source. The energy source hits objects and the reflected energy is detected and measured by sensors.
Distance to the object is determined by recording the time between transmitted and backscattered pulses and by using the speed of light to calculate the distance traveled.
3-D imaging can be achieved using both scanning and non-scanning systems. “3-D gated viewing laser radar” is a non-scanning laser ranging system that applies a pulsed laser and a fast gated camera. Research has begun for virtual beam steering using Digital Light Processing (DLP) technology.
What is LiDAR technology used for?
Airborne lidar (also airborne laser scanning) is when a laser scanner, while attached to an aircraft during flight, creates a 3-D point cloud model of the landscape. This is currently the most detailed and accurate method of creating digital elevation models, replacing photogrammetry.
One major advantage in comparison with photogrammetry is the ability to filter out reflections from vegetation from the point cloud model to create a digital terrain model that represents ground surfaces such as rivers, paths, cultural heritage sites, etc., which are concealed by trees.
Within the category of airborne lidar, there is sometimes a distinction made between high-altitude and low-altitude applications, but the main difference is a reduction in both accuracy and point density of data acquired at higher altitudes. Airborne lidar can also be used to create bathymetric models in shallow water.
Airborne lidar bathymetry:
The airborne lidar bathymetric technological system involves the measurement of the time of flight of a signal from a source to its return to the sensor. The data acquisition technique involves a seafloor mapping component and a ground truth component that includes video transects and sampling.
It works using a green spectrum (532 nm) laser beam. Two beams are projected onto a fast rotating mirror, which creates an array of points. One of the beams penetrates the water and also detects the bottom surface of the water under favorable conditions.
Terrestrial applications of lidar (also terrestrial laser scanning) happen on the Earth’s surface and can be either stationary or mobile.
Stationary terrestrial scanning is most common as a survey method, for example in conventional topography, monitoring, cultural heritage documentation, and forensics.
The 3-D point clouds acquired from these types of scanners can be matched with digital images taken of the scanned area from the scanner’s location to create realistic looking 3-D models in a relatively short time when compared to other technologies.
Each point in the point cloud is given the color of the pixel from the image taken located at the same angle as the laser beam that created the point.
Agricultural robots have been used for a variety of purposes ranging from seed and fertilizer dispersions, sensing techniques as well as crop scouting for the task of weed control.
Plant species classification
Controlling weeds requires identifying plant species. This could be done by using 3-D lidar and machine learning. Lidar produces plant contours as a “point cloud” with range and reflectance values.
Lidar has many uses in archaeology, including the planning of field campaigns, mapping features under the forest canopy, and overview of broad, continuous features indistinguishable from the ground. Lidar can produce high-resolution datasets quickly and cheaply.
Lidar-derived products could be easily integrated into a Geographic Information System (GIS) for analysis and interpretation.
Cruise Automation self-driving car with five Velodyne LiDAR units on the roof.
Autonomous vehicles may use lidar for obstacle detection and avoidance to navigate safely through environments. Point cloud output from the lidar sensor provides the necessary data for robot software to determine where potential obstacles exist in the environment and where the robot is in relation to those potential obstacles.
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