• LIDAR (Light Detection And Ranging, also LADAR) is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser..
The term "laser radar" is sometimes used, even thoughLIDAR does not employ microwaves or radio waves andtherefore is not radar in the strict sense of the word.LIDAR uses ultraviolet, visible, or infrared light toimage objects and can be used with a wide range oftargets, including non-metallic objects, rocks, rain,chemical compoundsA narrow laser beam can be used to map physical featureswith very high resolution.
This animation shows a LIDAR witha single beam scanned in one axis.The top image shows the scanningmechanismthe middle image shows the laserspath through a basic scenethe bottom image shows the sensorsoutput, after conversion from polar toCartesian coordinates.
What can we measure with lidar? • Clouds • Aerosol • Water vapour • Minor constituents e.g. ozone, hydrocarbons • TemperatureLidars can be used from the ground, aircraft or from space
Components used in lidar…1) Laser2) Scanner and optics3) Photodetector and receiver electronics4) Position and navigation systems
Laser• 600–1000 nm lasers are most common for non-scientific applications.• Better target resolution is achieved with shorter pulses, provided the LIDAR receiver detectors and electronics have sufficient bandwidth.
Scanners and optics• How fast images can be developed is also affected by the speed at which they are scanned.• Optic choices affect the angular resolution and range that can be detected. A hole mirror or a beam splitter are options to collect a return signal
Photodetector and receiver electronics• Two main photodetector technologies are used in From atmosphere Receiver lidars: solid state photodetectors, such as silicon avalanche photodiodes, or photomultipliers.• The sensitivity of the receiver is another parameter that has to be balanced in a LIDAR design.
Position and navigation systems- LIDAR sensors that are mounted on mobile platforms such as airplanes or satellites require instrumentation to determine the absolute position and orientation of the sensor.- Such devices generally include a Global Positioning System receiver and an Inertial Measurement Unit (IMU).
Applications..• Agriculture- LIDAR also can be used to help farmers determine which areas of their fields to apply costly fertilizer to achieve highest crop yeild. LIDAR can create a topographical map of the fields and reveals the slopes and sun exposure of the farm land.• Biology and conservation- LIDAR has also found many applications in forestry. Canopy heights, biomass measurements, and leaf area can all be studied using LIDAR systems. Similarly, LIDAR is also used by many industries, including Energy and Railroad, and the Department of Transportation as a faster way of surveying. Topographic maps can also be generated readily from LIDAR,
Continued..• Wind farm optimization-Lidar can be used to increase the energy output from wind farms by accurately measuring wind speeds and wind turbulence. An experimental lidar is mounted on a wind turbine rotor to measure oncoming horizontal winds, and proactively adjust blades to protect components and increase power.• Law enforcement- LIDAR speed guns are used by the police to measure the speed of vehicles for speed limit enforcement purposes
Advantages of LIDAR technologyThe other methods of topographic data collection are landsurveying, GPS, inteferrometry, and photogrammetry. LiDARtechnology has some advantages in comparison to these methods,which are being listed below:1) Higher accuracy2) Fast acquisition and processing3) Minimum human dependence- As most of the processes areautomatic unlike photogrammetry, GPS or land surveying. 4) Weather/Light independence- Data collection independentof sun inclination and at night and slightly bad weather.5) Canopy penetration-LiDAR pulses can reach beneath thecanopy thus generating measurements of points there unlikephotogrammetry.
Continued..6) Higher data density - Up to 167,000 pulses per second. More than 24 points per m2 can be measured. n Multiple returns to collect data in 3D.7) Cost - Is has been found by comparative studies that LiDAR data is cheaper in many applications. This is particularly considering the speed, accuracy and density of data.
Disadvantages• High operating costs (> £10k / hour)• Ineffective during heavy rain and/or low cloud/mist• Degraded at high Sun angles and reflections• Latency data not processed locally• Unreliable for water depth (< 2m) and breaking/turbulent waves• Lack of foliage/vegetation penetration• Precise alignment must be maintained
Future scopeThe lidar technology is now planned for a wide range of applications that canenable NASA’s achievement of its scientific and space exploration goals. Theseapplications fall into four general categories:a) Earth Science: long-duration orbiting instruments providing globalmonitoring of the atmosphere and landb) Planetary Science: orbiting or land-based scientific instruments providinggeological and atmospheric data of solar system bodiesc) Landing Aid: sensors providing hazard avoidance, guidance and navigationdatad) Rendezvous and Docking Aid : sensors providing spacecraft bearing,distance, and approach velocity
Summary• Lidar technique allows continuous monitoring of profiles with good height resolution• Different scattering mechanisms permit different kinds of measurement• New technology offers more compact sources and development of transportable and mobile systems