Lidar (Light Detection and Ranging) originated in the early 1960s, shortly after the invention of the laser. It mainly focuses on imaging, calculating distances of the target by illuminating a laser beam and measuring the time for a signal to return. The word “Lidar” was originally an acronym of “Emitting light” and “Radar”. Different types of scattering are used for different LIDAR applications such as: Rayleigh scattering, Mie scattering, Raman scattering, and fluorescence.
Lidar is popularly used to make high-resolution maps, includes applications in geodesy, geometrics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swath mapping (ALSM)and laser altimetry.
Its first applications came in meteorology, where the National Center for Atmospheric Research that was used to measure clouds.
How does LIDAR work?
The principle behind LiDAR is really quite simple.-Shine a small light at a surface and measure the time it takes to return to its source. When you shine a torch on a surface what you are actually seeing is the light being reflected and returning to your retina. Light travels very fast – about 300,000 kilometers per second, 186,000 miles per second or 0.3 meters per nanosecond so turning a light on appears to be instantaneous.
The actual calculation for measuring how far a returning light photon has travelled to and from an object is quite simple:
- Distance = (Speed of Light x Time of Flight) / 2
The LIDAR instrument fires rapid pulses of laser light at a surface, some at up to 150,000 pulses per second. A sensor on the instrument measures the amount of time it takes for each pulse to bounce back. Light moves at a constant and known speed so the LIDAR instrument can calculate the distance between itself and the target with high accuracy. By repeating this in quick succession the instrument builds up a complex ‘map’ of the surface it is measuring. With airborne LiDAR other data must be collected to ensure accuracy. As the sensor is moving height, location and orientation of the instrument must be included to determine the position of the laser pulse at the time of sending and the time of return. This extra information is crucial to the data’s integrity. With ground based LiDAR a single GPS location can be added for each location where the instrument is set up. Components of LIDAR system:
- Scanners and optics
- Photodetector and receiver
- Position and navigation system,
APPLICATIONS OF LIDAR :
Lidar has a wide range of applications which can be divided into airborne and terrestrial types. These different types of applications require scanners with varying specifications based on the data’s purpose, the size of the area to be captured, the range of measurement desired, the cost of equipment, and more.
- Agriculture: LIDAR helps the farmer to find the area that uses costly fertilizer. Both the layer information can be used to create high, medium and low crop production area. Extracted information will help farmer to save on the costly fertilizer.
- Forest Fire Management: LIDAR is becoming widely popular in forest fire management. Fire department is transforming from reactive to proactive fire management. LIDAR image helps to monitor the possible fire area which is called fuel mapping (fire behavior model).
- Precision Forestry: Precision Forestry is define as planning and operating the site specific forest area to increase the productivity of wood quality, reduce cost and increase profits, and maintain the environment. LIDAR and aerial photo is used to perform precision forestry.
- Environmental Assessment: Micro topography data generated form the LIDAR data is used in the environment assessment. Environment assessment is done to protect the plants and environment.
- River Survey: Under water information is required to understand depth, flow strength, width of the river and more. For the river engineering, its cross section data is extracted from LIDAR data (DEM) to create a river model, which will create flood way and flood fringe map.
- Modeling of the Pollution: LIDAR wavelength are shorter which operates in ultraviolet, visible region or near infrared. So LIDAR can detect pollutant particles of carbon dioxide, Sulphur dioxide and methane. This information helps researched to create pollutant density map of the area which can be used for better planning of the city.
- Mapping: Surface model created from LIDAR is used to add graphical value to maps. DEM (from LIDAR) is added underneath of all layers that shows the 3D view of the land.
- Management of Coastline: LIDAR data of the coastline surface and under the water surface can be combined by researches to analyze the wave’s behavior and area covered by them. If these data are captured periodically then marine scientist can understand the coastline erosion occurrence.
- Transport Planning: LIDAR data for road helps engineer to understand it and give a roadmap for the building it. As LIDAR are highly accurate technology it helps to technology it helps to understand width, elevation and length of the existing road.
- Mining: LIDAR is also used in the mining business in various task. It is used to measure the ore volume by taking series of photos of ore extraction space. These interval photos are used. These interval photos are used to calculate the volume.
- Glacier Volume Changes: LIDAR is used to calculate the glacier change over the period. LIDAR image are taken in time series to see the change happening. For example, LIDAR image was taken of Iceland from 2007-2009 and project was completed on 2012. These captured data will help scientist to know the amount of volume change
- Recording of Building: Ground based LIDAR can be used to record the inside of the house. It can be used to record the interior design too. This extracted data can be printed on the 3D printer to model it. Or when building is rebuild this when building is rebuild this recorded information can be used to restore the interior design.
- Vehicle Automation: LIDAR is becoming more popular in vehicles to make it automatic. LIDAR is used to grab the information on the road and it is passed to computerized system to make a human being like decision.
- Astronomy: In the exploration of MARS, LIDAR technology was used to create the topographic map of the red planet (the NASA Mars Global Surveyor). NASA\’s Phoenix Lander used LIDAR technology to the detect snow falling in the Mars atmosphere.
- Military: LIDAR has always been used by the military people to understand land. It creates high resolution map for the military purpose. They use LIDAR technology to understand the war place.
- COPS: It is quite common technology in the law enforcement department. Police uses LIDAR gun to detect the speed of the vehicle and also to understand the traffic flow. This technology is so precise that they can pick up the targeted vehicle from the cluttered traffic.
- Railway Infrastructure: Traditionally railway track measurement was done by regular survey system. Now LIDAR can quickly perform the measurements of the railway track and the topographical and surrounding area of the railway surrounding area of the railway path
- Tunnel Surveying: LIDAR is used to measure accurate and detailed measurements, used for analysis, assessment and modeling of the tunnel that is for railway track or road. This might be in the mountain, land or underwater.
- Tsunami Inundation Modeling: Tsunami is a well-known natural disaster and can takes thousand lives and damage infrastructure. LIDAR technology help scientist to understand the help scientist to understand the area that will be covered when Tsunami happens.
- Drones:These are now being used with laser scanners, as well as other remote sensors, as a more economical method to scan smaller areas. The possibility of drone remote sensing also eliminates any danger that crews of a manned aircraft may be subjected to in difficult terrain or remote areas.
Limitations of LIDAR on RADAR:
LIDAR’S are not really suited for small area surveys. LIDAR surveys are flown on slower aircraft and are typically a little less expensive to operate making them ideal for smaller areas. LIDAR systems are uniquely suited to low level, high accuracy surveys. Technology continues to evolve systems , LIDAR does not have a definite place in the market compared to RADAR Airborne RADAR surveys are suited to cover large areas quickly. Because they are also typically quite expensive to operate, they are not really suited for small area surveys.
#LIDAR does not provide superior penetration capability through any type of weather condition, and cannot be used in the day or night time.