Lidar (also called LIDAR , LIDAR , and LADAR ) is a survey method that measures distance to a target by illuminating the target with a pulsating laser beam and measuring the reflected pulse with the sensor. The laser return time difference and the wavelength can then be used to create a 3-D digital representation of the target. The name lidar , now used as an acronym light detection and range (sometimes light imaging, detection, and range ), was originally a portmanteau light and radar . Lidar is sometimes called laser scanning and 3-D scans , with terrestrial, air, and mobile applications.
Lidar is commonly used to create high resolution maps, with applications in geodesy, geomatics, archeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guides, air laser swift mapping (ALSM), and laser altimetry. This technology is also used in control and navigation for some autonomous cars.
Video Lidar
History and etymology
Lidar originated in the early 1960s, shortly after the invention of lasers, and laser-focused combined imagery with the ability to calculate distances by measuring time for signals to re-use appropriate sensors and electronic data acquisition. His first application came in meteorology, where the National Center for Atmospheric Research used it to measure clouds. The general public became aware of the accuracy and usefulness of the lidar system in 1971 during the Apollo 15 mission, when astronauts used laser altimeters to map the lunar surface.
Although now most sources treat the word "lidar" as an acronym, the term originates as a "light" and "radar" portmanteau. The mention of lidar was first published, in 1963, made this clear: "Finally a laser can provide a very sensitive detector of a certain wavelength of a distant object, while it is used to study the moon with 'lidar' (light radar).. "The Oxford English Dictionary supports this etymology.
The interpretation of "lidar" as an acronym ("LIDAR" or "LiDAR") came later, beginning in 1970, based on the assumption that since the basic term "radar" originally started as an abbreviation of "Radio Detection And Ranging", "LIDAR" "Detect Light And Start", or for "Laser Imaging, Detection And Start". Although English no longer treats "radar" as an acronym and printed text that universally presents the word uncapitalized, the word "lidar" is capitalized as "LIDAR" or "LiDAR" in several publications beginning in the 1980s. There is currently no consensus on capitalization, which reflects the uncertainty about whether or not "lidar" is an acronym, and if it is an acronym, whether it should appear in lower case, like "radar". Various publications refer to the lidar as "LIDAR", "LiDAR", "LIDaR", or "Lidar". USGS uses "LIDAR" and "lidar", sometimes in the same document; New York Times is predominantly using "lidar" for staff writing articles, although contributing news feeds like Reuters can use Lidar;
Maps Lidar
General description
Lidar uses ultraviolet light, visible, or near infrared to the image object. It can target a variety of materials, including non-metallic objects, stones, rain, chemical compounds, aerosols, clouds and even single molecules. A narrow laser beam can map physical features with very high resolution; for example, the plane can map a field with a resolution of 30 centimeters (12 inches) or better.
Lidar's essential concept came from EH Synge in 1930, which illustrates the use of powerful floodlights to investigate the atmosphere. Indeed, Lidar has since been widely used for atmospheric and meteorological research. Lidar instruments mounted to planes and satellites carry out surveys and mappings - the latest example is. NASA has identified lidar as a key technology to enable autonomous landing of landing vehicles in the months to come.
The wavelength varies according to the target: from about 10 micrometers to UV (about 250 nm). Usually light is reflected through back scattering, as opposed to pure reflections that may be found with a mirror. Different types of scattering are used for different lidar applications: Rayleigh scattering most often, Noodle scattering, Raman scattering, and fluorescence. The appropriate wavelength combinations enable the mapping of atmospheric contents remotely by identifying changes that depend on the wavelength on the intensity of the returned signal.
Design
In general there are two types of lidar detection schemes: detection of "incoherent" or direct energy (which essentially measures the amplitude change of reflected light) and coherent detection (best for measuring Doppler shifts, or reflected phase light changes). Coherent systems generally use optical heterodyne detection, which becomes more sensitive than direct detection, allowing them to operate at much lower power but at the expense of more complex transceiver requirements.
In both coherent and coherent lanes, there are two types of pulse models: micropulse lidar system and high energy system. The micropulse system using a dashed energy burst has evolved as a result of the ever-increasing amount of computer power available combined with advances in laser technology. They use less energy in the laser, usually on the order of one microjoule, and often "safe eyes", meaning they can be used without security precautions. High power systems are common in atmospheric research, where they are widely used to measure many atmospheric parameters: altitude, coating and cloud density, cloud particle properties (extinction coefficients, backscatter coefficients, depolarization), temperature, pressure, wind, moisture, and track gas concentration (ozone, methane, nitrogen oxide, etc.).
There are several major components to the lidar system:
- Lasers : 600-1000 nm lasers most common for non-scientific applications. They are not expensive, but because they can be focused and easily absorbed by the eye, the maximum strength is limited by the need to keep their eyes safe. Eye safety is often a requirement for most applications. A common alternative, 1550 nm lasers, is eye-safe at much higher power levels because these wavelengths are not focused by the eye, but the detector technology is less advanced and thus this wavelength is generally used over a longer range with more accuracy low. They are also used for military applications as 1550 nm is not visible in night vision goggles, unlike shorter 1000m infrared lasers. Topographic topographic scopes generally use a 1064moda pumped YAG diode laser, while bathymetry systems typically use 532 times the frequency of a diode pumped by a YAG laser because 532 mm penetrates water with much less damping than 1064 nm. The laser settings include a laser repetition rate (which controls the speed of data collection). Pulse length is generally an attribute of the laser cavity length, the amount of feed required through the gain material (YAG, YLF, etc.), and the Q-switch (pulsing) speed. Better target resolution is achieved with shorter pulses, provided that lidar and electronic receiver detectors have sufficient bandwidth.
- Scanners and optics : How quickly images can be developed is also affected by the speed of scanning. There are several options for scanning azimuth and elevation, including a double oscillating mirror plane, a combination with polygon mirrors and a dual axis scanner (see Laser scanning). Optical options affect the resolution and range of detectable angles. Mirror hole or file splitter is an option to collect the signal back.
- Electronic photodetector and receiver : Two major photodetector technologies are used in lidar: solid state photodetectors, such as silicon longside photographs, or photomultipliers. Receiver sensitivity is another parameter that must be balanced in lidar design.
- Position and navigation system : Lidar sensors mounted on a mobile platform such as an airplane or satellite require instrumentation to determine the absolute position and orientation of the sensor. Such devices generally include the recipient of the Global Positioning System and the Inertial Measurement Unit (IMU).
3-D imaging can be achieved using a scanning and non-scanning system. "3-D gated viewing laser radar" is a non-scanning laser system that starts applying pulsed lasers and fast gated cameras. Research has begun to drive virtual files using Digital Light Processing (DLP) technology.
Lidar imaging can also be performed using a high-speed detector array and sensitive modulation detector normally made on a single chip using a metal-oxide-semiconductor (CMOS) melting and CMOS/Charge-coupled device (CCD) hybrid fabrication technique. In this device each pixel performs local processing such as demodulation or gating at high speed, lowering the signal conversion to video level so that arrays can be read like cameras. Using this technique, thousands of pixels/channels can be obtained simultaneously. High resolution 3-D lidar camera using homodyne detection with electronic CCD or CMOS shutter.
A coherent imaging uses a synthetic array of heterodyne detection to allow deactivation of one receiving element to act as if it were an imaging array.
In 2014, Lincoln Laboratory announced a new imaging chip with more than 16,384 pixels, each capable of photographing one photon, enabling them to capture large areas in a single image. Previous technology generation with a quarter of the number of pixels sent by the US military after the January 2010 Haiti earthquake; a trajectory by a business jet on 3,000 meters (10,000 ft) above Port-au-Prince was able to capture an instant snapshot of a 600-meter-high square in a city of 30 cm (12 inches), displaying the precise altitude of debris littered on the road -the city street. The new system is 10x faster. This chip uses indium gallium arsenide (InGaAs), which operates in the infrared spectrum at relatively long wavelengths allowing for higher power and longer range. In many applications, such as self-driving cars, the new system will lower costs by not requiring mechanical components to drive the chip. InGaAs uses less harmful wavelengths than conventional silicon detectors, which operate at visual wavelengths.
Sensor
Unlike the passive sensors that detect the naturally emitted energy of an object, the lidar uses an active sensor that emits their own energy source for illumination. The energy source hits the object and the reflected energy of the object is detected and measured by the sensor. Lidar is an example of an active sensor and uses a laser (light amplification by radiated emission radiation) radar to transmit light pulses and receivers with sensitive detectors to measure backscattered or reflected light. The distance to the object is determined by recording the time between the transmitted and backscattered pulses and by using the speed of light to calculate the distance traveled.
Application type
Lidar has a variety of applications that can be divided into air and terrestrial types. These different types of applications require scanners with a variety of specifications based on the destination data, the size of the area to be taken, the desired range of measurements, the cost of the equipment, and more.
Lidar air
Airborne lidar (also airborne laser scanning ) is when the laser scanner, when attached to the aircraft during flight, creates a 3-D cloud point model of the landscape. This is the most detailed and accurate method of creating a digital elevation model, replacing photogrammetry. One of the main advantages over photogrammetry is the ability to filter reflections from vegetation from cloud point models to create models of digital surfaces representing the soil surface, such as streams, pathways, cultural heritage sites, etc., hidden by trees. In the category of the air lidar, sometimes there is a difference made between the application of high altitude and low altitude, but the main difference is the decrease in accuracy and density of data points obtained at higher altitudes. Lidar air can also be used to create bathymetric models in shallow water.
The main constituents of the lidar include a digital elevation model (DEM) and a digital surface model (DSM). The points and points of the ground are discrete point vectors while DEM and DSM are discrete raster grid interpolation points. This process also includes taking digital aerial photos. To interpret landslides in seats, for example, under vegetation, scars, stress cracks or treetop trees are used lidar. The digital elevation model of the aerial can see through the forest cover canopy, perform detailed measurements of scarps, erosion and tilt of power lines.
Air lidar data is processed using a toolbox called Toolbox for Data Filtering and Forest Study (TIFFS) for data filtering software and field studies. Data is interpolated to digital field models using software. The laser is directed to the area to be mapped and the height of each point above the ground is calculated by subtracting the original z coordinates from the appropriate digital field model heights. Based on this height above the ground non-vegetation data is obtained which may include objects such as buildings, power lines, flying birds, etc. The rest of the point is treated as a vegetation and is used for modeling and mapping. In each of these plots, lidar metrics are calculated by calculating statistics such as mean, standard deviation, skewness, percentile, mean squared, etc.
Airimetric lidar technology
The bathymetric lidar air technology system involves measuring the signal breakout time from the source back to the sensor. Data acquisition techniques involve the component of ocean floor mapping and ground truth components that include video and sampling transects. It works using a green spectrum laser beam (532 nm). Two beams are projected onto a rapidly spinning mirror, which creates various dots. One of the beams penetrates the water and also detects the underwater surface under favorable conditions.
The data obtained show the surface area exposed on the seabed. This technique is very useful because it will play an important role in the major ocean floor mapping program. Mapping generates onshore topography as well as below water elevation. The reflection of the sea floor is another solution product of this system that can benefit the mapping of underwater habitats. This technique has been used for mapping three-dimensional images of California waters using lidar hydrography.
Drones are now used with laser scanners, as well as other remote sensors, as a more economical method for scanning smaller areas. The possibility of remote sensing of the drone also eliminates the dangers posed by the manned crew may be in difficult terrain or remote areas.
Terrestrial Lidar
The terrestrial lidar app (also terrestrial laser scanning ) occurs on the surface of the Earth and can be still or moving. Stationary terrestrial scans are most commonly used as survey methods, for example in conventional topography, monitoring, documentation of cultural heritage and forensics. The 3-D point clouds obtained from this type of scanner can be matched with digital images taken from the scanned area of ​​the scanner location to create a realistic 3-D model in a relatively short time compared to other technologies. Every point in the cloud point is given the pixel color of the captured image lying at the same angle as the laser beam that creates the point.
Mobile lidar (also mobile laser scanning ) is when two or more scanners connect to a moving vehicle to collect data along the path. These scanners are almost always paired with other types of equipment, including GNSS and IMU recipients. One example of the application is a survey of streets, where the power grid, proper bridge heights, bordering trees, etc. all need to be taken into account. Rather than collecting each of these measurements individually in the field with a tachymeter, a 3-D model from a cloud point can be made where all the necessary measurements can be made, depending on the quality of the data collected. This eliminates the problem of forgetting to take measurements, provided the model is available, reliable and has the right accuracy level.
Terrestrial lidar mapping involves the mapping process of the occupant map. This process involves an array of cells that are divided into grids that use the process to store elevation values ​​when the lidar data falls into each grid cell. Binary maps are then created by applying a certain threshold to the cell value for further processing. The next step is to process the radial and z-coordinate distance of each scan to identify which 3-D point corresponds to each particular grid cell that leads to the data formation process.
Data formation
For autonomous applications, LIDAR with 3-D scanners is used for barrier detection and avoiding collisions. The scanner measures the radial distance at different angular resolutions. The lidar emits a single laser beam and uses an interior spinning mirror to distribute a laser beam covering a wide field of view.
Object detection
The object detection procedure consists of three steps: Calculation of laser point feature and previous filtering, 3-D segmentation, object classification and 2-D position calculation. Features for segmentation are calculated around fixed radiial distances in 2-D and 3-D. These include:
Amplitude density
It involves the percentage points around it with an amplitude value below a certain threshold. Points with a lower density of threshold removed from segmentation and further processing.
Altitude above local minimum within 2-D search radius
In this case, dots that have a lower elevation than a certain threshold are removed. In cloud point segmentation, all segments that meet criteria by object are included in individual objects.
Benefits
The main advantages of object detection and data formation are high dot density and high spatial resolution obtained. Also the accuracy of the obtained data sets increases to a considerable degree.
Disadvantages
Although a large amount of research has been done for object classification of 3-D point clouds, direct extraction from individual points of lidar input has not been achieved.
Object detection for transport system
In the transport system, to ensure the safety of vehicles and passengers and to develop electronic systems that provide driver assistance, understanding the vehicle and the surrounding environment is very important. The Lidar system plays an important role in transport system security. Many electronic systems that add driver and vehicle safety assistance such as Adaptive Cruise Control (ACC), Emergency Brake Assist, Anti-lock Braking System (ABS) rely on vehicle environment detection to act autonomously or semi-autonomously. Lidar mapping and estimation achieve this.
Overview: The current lidar system uses a rotating hexagonal mirror that breaks the laser light. The top three beams are used for vehicles and obstacles in the front and the lower beam is used to detect road markings and road features. The main advantage of using lidar is that spatial structure is obtained and this data can be combined with other sensors such as radar, etc. To get a better picture of the vehicle environment in terms of static and dynamic properties of objects in the Living environment.
Apps
There are various applications for lidar, in addition to the applications listed below, as is often mentioned in the National lidar dataset program.
Agriculture
Autonomous robots have been used for various purposes in agriculture ranging from seed and fertilizer distribution, sensing techniques, and plant scouting to weed control tasks.
Lidar can help determine where to use expensive fertilizer. This can create a topographical map of the field and reveal the slopes and sun exposure of farmland. Researchers at the Agricultural Research Service used this topographic data with agricultural crop yields from previous years, to categorize the land into high, medium, or low yield zones. It shows where to apply fertilizer to maximize yield.
Other applications are plant mapping in gardens and vineyards, to detect foliage growth and other pruning or maintenance needs, to detect variations in fruit production, or to calculate crops.
Lidar is useful in GPS rejected situations, such as peanut and fruit gardens, where GPS signal beams come to precision agricultural equipment or unlicensed tractors. The Lidar sensor can detect line edges, so farm equipment can keep moving until the GPS signal is rebuilt.
Classification of plant species
Weed control requires identification of plant species. This can be done using 3-D lidar and machine learning. Lidar produces plant contours as "cloud point" with range and reflectance values. This data is modified, and the feature is extracted from it. If the species is known, the feature is added as new data. Species labeled and its features were originally stored as examples to identify species in the real environment. This method is efficient because it uses low resolution petals and supervised learning. It includes easy to calculate feature sets with general statistics features independent of factory size.
Archeology
Lidar has many uses in archeology, including field campaign planning, mapping features under the forest canopy, and an overview of extensive and sustainable features that can not be distinguished from the ground. Lidar can produce high resolution datasets quickly and cheaply. Products derived from Lidar can be easily integrated into Geographic Information Systems (GIS) for analysis and interpretation.
Lidar can also help create high resolution digital elevation models (DEMs) from archaeological sites that can reveal micro topography that is otherwise hidden by vegetation. The lidar signal intensity can again be used to detect features buried beneath a vegetated surface as flat as the plane, especially when mapped using the infrared spectrum. The presence of these features affects plant growth and thus the amount of infrared light is reflected back. For example, at Fort Beausà © jour - Fort Cumberland National Historic Site, Canada, lidar discovered archaeological features associated with the Fort siege in 1755. The indistinguishable feature on the ground or through aerial photographs was identified by coating the hills. DEM is made with artificial lighting from various angles. Another example is working at Caracol by Arlen Chase and his wife Diane Zaino Chase. In 2012, lidar is used to locate the legendary city of La Ciudad Blanca or the "City of the Monkey God" in the La Mosquitia region of the Honduran jungle. During the seven-day mapping period, evidence is found from man-made structures. In June 2013, the rediscovery of Mahendraparvata city was announced. In southern New England, lidar is used to reveal rock walls, foundations of buildings, abandoned streets, and other landscape features obscured in aerial photographs by the dense forest canopy of the region. In lndar, lidar data is used by Demian Evans and Roland Fletcher to reveal anthropogenic changes to the landscape of Angkor. By 2016, Lidar was used to map the ancient Maya in northern Guatemala, discovering 17 elevated roads connecting the ancient city of El Mirador to other sites. In 2018, lidar archaeologists discovered more than 60,000 man-made structures in the Maya Biosphere Reserve, a "major breakthrough" that shows Maya civilization much larger than previously thought.
Autonomous vehicles
Autonomous vehicles can use lidar for barrier detection and avoidance to navigate safely through the environment, using a rotating laser beam. The cost map or the cloud output point of the lidar sensor provides the data needed for the robot software to determine where potential obstacles exist in the environment and where the robot is in relation to such potential hurdles. Singapore Singapore-MIT Research and Technology Alliance (SMART) is actively developing technology for autonomous lidar vehicles. Examples of companies that produce lidar sensors commonly used in robotics or automation of vehicles are Sick and Hokuyo. Examples of inhibition and avoidance detection products utilizing lidar sensors are Autonomous Solutions, Inches 3D Laser Systems and Velodyne HDL-64E.
The first generation of automotive adaptive cruise control system uses only lidar sensors.
Lidar data processing approach
Below are various LIDAR data processing approaches and use them along with data from other sensors through the fusion sensor to detect the environmental conditions of the vehicle.
GRID based process using 3-D lidar and fusion with radar measurement
In this method, proposed by Philipp Lindner and Gerd Wanielik, laser data is processed using multidimensional residential networks. Data from a four-layer laser is processed earlier at the signal level and then processed at a higher level to extract obstacle features. A combination of two- and three-dimensional grid structures is used and the space within this structure is tied to several discrete cells. This method allows large amounts of raw measurement data to be handled effectively by collecting it in spatial containers, cells from the evidence grid. Each cell is associated with a probability measure that identifies the cell occupation. This probability is calculated by measuring the range of lidar sensors obtained over time and the measurement of new ranges, associated with using the Bayes theorem. A two-dimensional grid can observe obstacles in front of it, but can not observe the space behind the obstacles. To counter this, the unknown state behind the obstacle is given a probability of 0.5. By introducing a third dimension or in other terms using a multi-layer laser, the spatial configuration of an object can be mapped into the grid structure to a level of complexity. This is achieved by transferring the measurement point into the three-dimensional lattice. The grid cells that are occupied will have a probability greater than 0.5 and the mapping will be color-coded based on probability. Unallocated cells will have a probability of less than 0.5 and this area will usually be a white space. This measurement is then converted to a grid coordinate system using the position of the sensor on the vehicle and the position of the vehicle in the world coordinate system. The coordinate of the sensor depends on its location on the vehicle and the vehicle coordinates are calculated using egomotion estimation, which estimates the movement of the vehicle relative to the rigid scene. For this method, the grid profile must be defined. Grid cells touched by transmitted laser beams are calculated by applying the Bresenham line algorithm. To obtain spatial expansion structures, analysis of the connected components of these cells is performed. This information is then passed to a rotating caliper algorithm to obtain the spatial characteristics of the object. In addition to lidar detection, RADAR data is obtained by using two short-range integrated radar to gain additional dynamic properties of the object, such as speed. Measurements are assigned to objects using a potential distance function.
Advantages and disadvantages
The geometric features of the object are efficiently extracted, from measurements obtained by the 3-D occupancy grid, using a rotating caliper algorithm. Integrating radar data into lidar measurements provides information about the dynamic nature of obstacles such as speed and location of obstacles with respect to the location of sensors that help the vehicle or driver decide what actions to take to ensure safety. The only concern is the computational requirement to apply this data processing technique. This can be applied in real time and has proven to be efficient if the size of the 3-D occupancy grid is very limited. But this can be increased to a wider range by using special spatial datastructures that manipulate spatial data more effectively, for 3-D grid representation.
3-D lidar blend and color camera for multiple object detection and tracking
The framework proposed in this method by Soonmin Hwang et al., Is divided into four steps. First, data from the camera and lidar 3-D are inserted into the system. Both the input of the lidar and the camera are obtained in parallel and the color image of the camera is calibrated with lidar. To improve efficiency, sampling of horizontal 3-D points is applied as pre-processing. Second, the segmentation stage is where all 3-D points are split into several groups per distance from the sensor and the local plane from the plane close to the remote plane are consecutively estimated. Local aircraft are estimated to use statistical analysis. A group of points closer to the sensor is used to calculate the initial field. By using the current local plane, the next local plane is estimated with iterative updates. The object proposal in the 2-D image is used to separate the foreground object from the background. For faster and more accurate detection and tracking of Binarized Normed Gradient for Objectness Estimation at 300fps is used. BING is a combination of normalized gradients and binary versions that accelerate feature extraction and testing processes, to estimate the objectivity of the image window. In this way the foreground and background objects are separated. To form objects after estimating the image objectivity using BING, the 3-D points are grouped or grouped. Clustering is done using the DBSCAN (Density-Based Spatial Clustering of Applications with Noise) algorithm that can be strong due to less-parametric characteristics. Using 3-D points, ie 3-D segments, a more accurate region-of-interest (ROI) is generated by projecting 3-D points in 2-D images. The third step is detection, which is broadly divided into two parts. First is the object detection in 2-D images achieved using Fast R-CNN because this method does not require training and also takes into account drawings and some interesting areas. Second is object detection in 3-D space which is done by using spin image method. This method extracts local and global histograms to represent a particular object. To combine 2-D drawing results and detection of 3-D space objects, the same 3-D region is considered and two independent classifiers of 2-D images and 3-D space are applied to the area under consideration. A calibration score was performed to obtain a single confidence score from both detectors. This single value is obtained in the form of probability. The final step is tracking. This is done by hooking moving objects in the current and previous frames. For object tracking, segment matching is adopted. Features such as averages, standard deviations, quantized color histograms, volume sizes and the number of 3-D points of a segment are calculated. Euclidean distance is used to measure differences between segments. To assess the look and disappearance of an object, a similar segment (obtained by Euclidean distance) of two different frames is taken and the physical distance and the inequality score are calculated. If the score exceeds the range for each segment in the previous frame, the tracked object is considered to have disappeared.
Advantages and disadvantages
The advantage of this method is to use 2-D images and 3-D data together, F l-score (which gives a measure of test accuracy), the average precision (AP) is higher than that when only 3-D data from lidar is a trace. This score is a conventional measure that assesses the framework. The disadvantage of this method is the use of BING for object proposal estimation because BING predicts a small set of object bound boxes.
Detection of obstacles and the introduction of a road environment using lidar
This method was proposed by Kun Zhou et al. not only focusing on object detection and tracking but also recognizing trajectory and path marking features. As mentioned earlier the lidar system uses a rotating hexagonal mirror that divides the laser beam into six beams. The top three layers are used to detect objects forward such as vehicles and objects on the roadside. Sensors are made of weatherproof material. Data detected by lidar are grouped into several segments and tracked by Kalman filters. The data groupings here are based on the characteristics of each segment based on the object model, which distinguishes different objects such as vehicles, signboards, etc. These characteristics include object dimensions, etc. The reflector on the rear edge of the vehicle is used to distinguish the vehicle from other objects. The object tracking is done using a 2-stage Kalman filter considering the stability of the tracking and the accelerated motion of the object. Lidar reflective intensity data is also used for distance detection by using strong regression to handle occlusion. Road marks are detected using the modified Otsu method by differentiating rough and glossy surfaces.
Advantages
Roadside reflectors that show boundary lines are sometimes hidden for various reasons. Therefore, other information is needed to recognize the border of the road. Lidar used in this method can measure the reflectivity of the object. Therefore, with the limit of the way this data can also be recognized. Also the use of sensors with weatherproof heads helps detect objects even in adverse weather conditions. High Canopy The model before and after the flood is a good example. Lidar can detect high detailed canopy height data as well as its road border.
Benefits of using lidar measurements
Lidar measurements help identify barrier spatial structures. It helps distinguish objects by size and estimates the impact of driving on them.
The Lidar system provides better coverage and a wide field of view that helps detect obstacles on the curve. This is one of the main advantages over a RADAR system that has a narrow field of view. The fusion of lidar measurements with different sensors makes the system powerful and useful in real-time applications, since dependar dependent systems can not estimate dynamic information about detected objects.
It has been proven that lidar can be manipulated, like self-driving cars are tricked to take evasive action.
Biology and conservation
Lidar has also found many applications in the field of forestry. The height of the canopy, the measurement of biomass, and the leaf area can all be studied using the air lidar system. Likewise, lidar is also used by many industries, including Energy and Railways, and the Department of Transportation as a way of faster survey. Topographic maps can also be generated easily from lidar, including for recreational use such as in making orientation maps.
In addition, Save-the-Redwoods League is undertaking a project to map high redwood trees on the coast of Northern California. Lidar allows research scientists to not only measure the height of previously uncharted trees, but to determine the biodiversity of redwood forests. Stephen Sillett, who works with the League on the North Coast lidar project, claims this technology will be useful in directing future efforts to preserve and protect ancient redwood trees.
Geology and soil science
High resolution digital elevation maps produced by air and stationary lanes have led to significant advances in geomorphology (geoscience branches related to the origin and evolution of Earth's surface topography). The ability of lidar to detect fine topographic features such as river terraces and river channel banks, to measure ground level elevations beneath the vegetation canopy, to complete better spatial elevation derivatives, and to detect elevation changes between recurrent surveys has enabled many new studies of physical processes and the chemistry that forms the landscape. In 2005 the Round Tour at Mont Blanc massif became the first high alpine mountain in which the lidar was employed to monitor the increasing occurrence of severe rock falls on the surface of large rocks allegedly caused by climate change and permafrost degradation at high altitudes.
In geophysics and tectonics, the combination of lidar-based aircraft and GPS has evolved into an important tool for detecting errors and for measuring lifting. The outputs of both technologies can produce highly accurate elevation models for terrain - models that can even measure the height of the soil through the trees. This combination is used most notably to find the location of the Seattle Fault in Washington, USA. This combination also measures the appointment at Mt. St. Helens using data from before and after the 2004 appointment. The lidar system monitors glaciers and has the ability to detect subtle amounts of growth or decline. The satellite-based system, ICESat NASA, includes a lidar sub-system for this purpose. NASA Airborne Topographic Mapper is also used extensively to monitor glaciers and perform coastal change analyzes. This combination is also used by soil scientists when making land surveys. Detailed terrain modeling allows soil scientists to see changes in tilt and landform changes that show patterns in the spatial relations of the soil.
Remote atmospheric and meteorological sensing
Originally based on a ruby ​​laser, lidar for meteorological applications was built shortly after the invention of the laser and was one of the first applications of laser technology. Lidar technology has grown enormously in capabilities and the lidar system is used to perform a variety of measurements that include cloud profiling, wind gauge, aerosol study, and measuring various atmospheric components. The atmospheric component in turn can provide useful information including surface pressure (by measuring the absorption of oxygen or nitrogen), greenhouse gas emissions (carbon dioxide and methane), photosynthesis (carbon dioxide), fire (carbon monoxide), and moisture (moisture). The atmospheric lidar can be ground, air or satellite based on the type of measurement.
The remote sensing of the lidar atmosphere works in two ways -
- by measuring the backscatter of the atmosphere, and
- by measuring the scattered reflections from the ground (when the lidar is in the air) or other hard surfaces.
Backscatter from the atmosphere directly gives the size of cloud and aerosol. Other derivative measurements of backscatter such as wind or cirrus ice crystals require careful selection of wavelength and/or polarization. Lidar Doppler and Rayleigh Doppler lidar are used to measure the temperature and/or wind speed along the rays by measuring the frequency of backscattered light. The Doppler expands the moving gas enabling the determination of properties through the resulting frequency shift. Scanning lidars, such as the NASA HARLIE LIDAR cone scanner, have been used to measure atmospheric wind speeds. The ESA ADM-Aeolus wind mission will be fitted with a Doppler lidar system to provide global vertical wind profile measurements. The lidar doppler system was used at the 2008 Summer Olympics to measure wind farms during yacht competitions.
The Doppler lidar system is also now beginning to be successfully applied in the renewable energy sector to obtain wind speed, turbulence, wind, and wind shear data. Both pulsed and continuous wave systems are used. The pulse system uses the signal time to obtain a vertical distance resolution, while the continuous wave system depends on the detector focusing.
The term, eolics , has been proposed to describe collaborative and interdisciplinary studies of the wind using a computational fluid mechanics simulation and Doppler lidar measurement.
The soil reflections from the air lane provide a measure of surface reflectivity (assuming atmospheric transmittance is known) at the lidar wavelength, however, soil reflection is usually used to make atmospheric absorption measurements. "Differential absorption lidar" (DIAL) measurements use two or more close-range (& lt; 1Ã,nm) wavelengths to factor out surface reflectivity as well as other transmission losses, since these factors are relatively insensitive to wavelength. When tuned to the proper absorption channel of a particular gas, DIAL measurements can be used to determine the concentration (mixing ratio) of a particular gas in the atmosphere. This is called the Integrated Path Differential Absorption (IPDA) approach, as it is an integrated sequestration measure throughout the entire lidar path. The IPDA tongue can be either pulsed or CW and usually uses two or more wavelengths. The IPDA tongue has been used for remote sensing of carbon dioxide and methane.
Array of synthetic arrays enables LIDAR imaging without the need for array detectors. Can be used for imaging Doppler velocimetry, ultra-fast frame rate (MHz) imaging, as well as for speckle reduction in coherent lidar. A broad lidar bibliography for atmospheric and hydrospheric applications is given by Grant.
Scheimpflug Principles
Another lidar technique for remote sensing of the atmosphere has emerged. It is based on the Scheimpflug principle called scheimpflug lidar (slidar).
"The implication of the Scheimpflug principle is that when a laser beam is transmitted to the atmosphere, the back scattering echo from the entire volume of the illuminated probe is still in focus simultaneously without reducing the aperture as long as the object plane, the image area and the lens plane intersect each other ". Two-dimensional CCD/CMOS cameras are used to resolve the back scattering echoes of transmitted laser beams.
So as in the case of conventional lidar technology a continuous wave light source such as a diode laser can be used for remote sensing rather than using a second elaborate nanoscale light source. The SLIDAR system is also a powerful and inexpensive system based on compact laser diodes and array detectors.
Law enforcement
The lidar speed gun is used by the police to measure the speed of the vehicle for the purpose of speed limit enforcement. In addition, it is used in forensics to assist in crime scene investigations. Scene scanning is taken to record details of object placement, blood, and other important information for review later. This scan can also be used to determine the bullet trajectory in case of shooting.
Military
Only a few military applications are known to be in place and classified (such as measuring the speed of the AGM-129 ACM stealth missile cruise missile), but a large amount of research is being done in its use for imaging. Higher resolution systems collect enough detail to identify targets, such as tanks. Examples of lidar military applications include the Air Laser Mine Detection System (ALMDS) for mine-fight warfare by AretÃÆ'Â © Associates.
The NATO report (RTO-TR-SET-098) evaluates potential technologies for direct detection of biological warfare discrimination. Potential technologies evaluated were Long-Wave Infrared (LWIR), Differential Scattering (DISC), and Ultraviolet Laser Induced Fluorescence (UV-LIF). The report concludes that: Based on the results of the lidar systems tested and discussed above, the Task Group recommends that the best option for the application of short-term dead detection systems (2008-2010) is UV-LIF However, in the long term , other techniques such as Raman stand-off spectroscopy may prove useful for the identification of biological war agents.
Lidar's short-range compact spectrometric based on Laser-Induced Fluorescence (LIF) will address the presence of bio-threats in the form of aerosols over important indoor, semi-closed and outdoor places such as stadiums, subway and airports. This near-real time capability will allow rapid detection of bioaerosol release and enable timely implementation of measures to protect occupants and minimize contamination levels.
The Remote Biological Lie Detection System (LR-BSDS) was developed for the US Army to provide the fastest initial hostage warning against biological attacks. It is an air system carried by helicopters to detect synthetic aerosol clouds that contain biological agents and chemicals over long distances. The LR-BSDS, with a detection range of 30 km or more, deployed in June 1997. Five lidar units produced by German company Sick AG were used for short-range detection at Stanley, an autonomous car that won the DARPA Grand Challenge 2005.
The Boeing AH-6 robot made a fully autonomous flight in June 2010, including avoiding obstacles using lidar.
Mine
For ore volume calculation is achieved by periodic (monthly) scanning in the ore removal area, then comparing surface data with the previous scan.
The Lidar sensor can also be used for barrier detection and avoidance for robotic mining vehicles such as the Komatsu Automobile Transportation System (AHS) used at Rio Tinto's Future Mine.
Physics and astronomy
An observatory network around the world uses lidar to measure the distance to reflectors placed on the moon, allowing the position of the moon to be measured by millimeter precision and general relativity tests to be performed. MOLA, Mars Orbiting Laser Altimeter, uses lidar instruments on Mars orbiting satellites (NASA Mars Global Surveyor) to produce a spectacular global topographic survey of the red planet.
In September 2008, NASA Phoenix Lander used lidar to detect snow in the atmosphere of Mars.
In atmospheric physics, lidar is used as a remote detection instrument to measure the density of certain elements of the middle and upper atmosphere, such as potassium, sodium, or molecular nitrogen and oxygen. This measurement can be used to calculate the temperature. Lidar can also be used to measure wind speed and to provide information about the vertical distribution of aerosol particles.
At the JET nuclear fusion research facility, in the United Kingdom near Abingdon, Oxfordshire, lidar Thomson Scattering is used to determine the profile of plasma electron density and temperature.
Mechanics bar
Lidar has been widely used in rock mechanics for rock mass characterization and slope change detection. Some important geomechanical properties of rock mass can be extracted from 3-D point clouds obtained by using lidar. Some of these traits are:
- Orientation of discontinuity
- Distance discontinuity and RQD
- Aperture discontinuity
- Persistence discontinuity
- The roughness of discontinuity
- Water infiltration
Some of these properties have been used to assess the geomechanical quality of rock mass through the RMR index. Moreover, since the discontinuity orientation can be extracted using the existing methodology, it is possible to assess the geomechanical quality of the slope of the stone through the SMR index. In addition, different 3-D point cloud comparisons from the slope obtained at different times allow the researcher to study the changes generated at the scene during this time interval as a result of rain stones or other landslides processes.
THOR
THOR is a laser designed to measure Earth's atmospheric conditions. The laser enters the cloud cover and measures the thickness of the halo back. The sensor has a fiber optic aperture with a width of 7.5 inches which is used to measure back light.
Robotics
Lidar technology is being used in robotics for environmental perception as well as object classification. The ability of lidar technology to provide three-dimensional elevation maps of terrain, high precision distance to the ground, and speed of approach can enable safe landing of robots and manned vehicles with a high degree of precision.. Lidar is also widely used in robotics for localization and mapping simultaneously and well integrated into the robot simulator. See the Military section above for more examples.
Spaceflight
Lidar is increasingly used to calculate the rangefinding and orbital elements of relative speed in proximity operations and the arrangement of spacecraft stations. Lidar has also been used for atmospheric studies from outer space. Short pulses of laser light emitted from the spacecraft can reflect tiny particles in the atmosphere and return to a telescope that is aligned with the spacecraft's laser. By precisely regulating the 'echo' time, and by measuring how many laser beams are received by the telescope, scientists can accurately determine the location, distribution and nature of the particles. The result is a revolutionary new tool for studying atmospheric constituents, from cloud droplets to industrial polluters, which are hard to detect in other ways. "
Survey
Water lidar sensors are used by companies in the field of remote sensing. They can be used to create a DTM (Digital Terrain Model) or DEM (Digital Elevation Model); this is fairly common for larger areas because the aircraft can get as wide as 3-4 km in one overpass. Vertical accuracy larger than 50 mm can be achieved with a lower flyover, even in the forest, where it is able to provide canopy height and ground elevation. Typically, GNSS recipients configured via georeference control points are required to connect data with WGS (World Geodetic System).
LiDAR is also used in hydrographic surveys. Depending on the water clarity LiDAR can measure depth from 0.9 m to 40 m with a vertical accuracy of 15 cm and a horizontal accuracy of 2.5 m.
Kehutanan
The Lidar system has also been applied to improve forest management. Measurements are used to carry out inventories in forest plots as well as calculate the height of individual trees, crown width and crown diameter. Other statistical analyzes use lidar data to estimate total plot information such as canopy volume, average, minimum and maximum altitude, and estimated vegetation cover.
Transportation
Lidar has been used in the rail industry to produce asset health reports for asset management and by the transport department to assess their road conditions. CivilMaps.com is a leading company in its field. Lidar has been used in adaptive shipping control system (ACC) for cars. Systems such as those of Siemens, Hella, and Cepton use lidar devices mounted on the front of the vehicle, such as bumpers, to monitor the distance between any vehicle and vehicle in front of it. If the vehicle in front slows down or gets too close, the ACC applies the brakes to slow down the vehicle. When the road ahead is clear, the ACC allows the vehicle to accelerate to the speed set by the driver. See the Military section above for more examples. A lidar-based device, Ceilometers are used at airports around the world to measure cloud altitude on the runway approach path.
Window optimization
Lidar can be used to increase the energy output of wind farms by accurately measuring wind speed and wind turbulence. The experimental lidar system can be mounted on a nacelle from a wind turbine or integrated into a rotating spinner to measure the coming horizontal wind, wind behind wind turbines, and proactively adjust the blades to protect components and increase power. Lidar is also used to characterize incident wind sources for comparison with the production of wind turbine power to verify the performance of wind turbines by measuring the wind turbine power curve. Wind farm optimization can be considered as a topic in applied eolics .
Optimization of solar photovoltaic use
Lidar can also be used to assist planners and developers in optimizing photovoltaic solar systems at the city level by determining the exact roof tops and for determining shadow losses. Recent air lashing scanning efforts have focused on ways to estimate the amount of sunlight that affects vertical building facades, or by incorporating more detailed shading losses taking into account the effects of vegetation and the larger surrounding areas.
Video game
Recent simulation racing games such as iRacing, Assetto Corsa and Project CARS increasingly feature reproducible racing tracks from 3-D point clouds obtained through the Lidar survey, which produces replicated surfaces with millimeter precision in the 3-D environment in the game.
2017's Scanner Sombre exploration game, by Introversion Software, uses Lidar as a fundamental game mechanic.
Other uses
The video for the song "House of Cards" by Radiohead is believed to be the first use of a real-time 3-D laser scan to record music videos. The range data in the video is not entirely from a lidar, since a structured light scan is also used.
Alternate technology
The latest development of Structure From Motion (SFM) technology enables the delivery of 3-D images and maps based on data taken from visual and IR photography. Elevation or 3-D data is extracted using multiple parallel passes over the mapped area, producing visual light images and 3-D structures of the same sensor, which are often specially selected and calibrated digital cameras.
See also
References
Further reading
- Heritage, E. (2011). 3D laser scanning for inheritance. Advice and guidance to the user about laser scanning in archeology and architecture. Available at www.english-heritage.org.uk. [2]
- Inheritance, G., & amp; Large, A. (Eds.). (2009). Laser scanning for environmental science. John Wiley & amp; Children. ISBN: 1-4051-5717-8
- Maltamo, M., NÃÆ'Â|sset, E., & amp; Vauhkonen, J. (2014). Application of Forestry Aeronautical Scanning: Concepts and Case Studies (Vol 27). Springer Science & amp; Business Media. ISBNÃ, 94-017-8662-3
- Shan, J., & amp; Toth, C. K. (Eds.). (2008). Laser and topographic scanning: principles and processing. Press CRC. ISBN: 1-4200-5142-3
- Vosselman, G., & amp; Maas, H. G. (Eds.). (2010). Scanning the air and ground lasers. Whittles Publishing. ISBNÃ, 1-4398-2798-2
External links
- USGS Center for LIDAR Information Coordination and Knowledge (CLICK) - A website intended to "facilitate data access, user coordination and remote sensing lidar education for scientific needs."
- Free online lidar data viewer
- Lidar Industry News and Education
Source of the article : Wikipedia
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