Light detection and ranging technology Seminar By: Md Hyder Hussain Pasha

 Introduction  LIDAR : what??? why??? how???  Ranging of LIDAR  Components  Basic principle of operation  Traditional photography Vs LIDAR  Advantages & Disadvantages of LIDAR  Application  Conclusion  References OUTLINE

 Light detection and ranging(LIDAR) is an optical Remote Sensing Technology that can measure the distance to an object or surface.  It is similar to Radar, but it incorporates laser pulses rather than radio waves. What is lidar???

 LIDAR uses Ultraviolet, Visible or near Infrared light to image objects and can be used with a wide range of targets, including non metallic objects, rocks, rain, chemical compounds, aerosals, clouds and even single molecules.  A narrow laser beam can be used to map physical features with very high resolution. Why lidar???

 It works similar to RADAR.  Each time the LASER(Light Amplification by Stimulated Emission of Radiations) generates an optical pulse.  This pulse is reflected off an object and returns to the system receiver.  High speed counter measures the time of flight from the start pulse to the return pulse.  Time measurement is converted to a distance. How???

Lidar systems collect height and elevation data using light from the near-infrared wavelength

 LIDAR systems can emit pulses at rate > 1,00,000 pulses per second referred to as Pulse Repetition Frequency.  A pulse of laser light travels at ‘C’, the speed of light.  The travelling time of a pulse of light ‘t’ is t = 2( R/C ) Ranging of lidar

 LASER  SCANNER AND OPTIC  PHOTODETECTOR AND RECEIVER  POSITION AND NAVIGATIONAL SYETEM components

 nm Laser are most common for non- scientific applications.  Air borne topographic mapping lidars generally use 1064 nm diode pumped YAG Lasers.  Better target resolution is achieved with shorter pulses, provided the Lidar Receiver Detector and electronics have sufficient bandwidth. LASER

 How fast images can be developed is also affected by the speed at which it can be scanned into system.  There are several options to scan the elevation, including Dual Oscillating Plane Mirror, a combination with a Polygon Mirror, a Dual Axis Scanner. Scanner and optics

Two main Photodetector technologies used in LIDARS are:-  Silicon Avalanche Photodiodes  Photo Multipliers photodetector

 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 (GPS)Receiver and an Inertial Measurement Unit (IMU). Navigational system

 Here pulses of light emitted into the atmosphere and scattered back by clouds, aerosals or air molecules.  Then light is collected by a telescope.  Thereafter Spectrometers or Interference filters isolate the wavelength concerned.  Time of flight gives the scattering altitude Basic principle Z = 2.c.t

Traditional PHOTOGRAPHY  Day time data collection only.  Complicated and sometimes unreliable procedures.  Planimetric accuracy is better than vertical accuracy. LIDAR  Day or night data acquisition.  Direct acquisition of 3D collection.  Vertical accuracy is better than planimetric accuracy. vs

 Higher accuracy.  Fast acquisition and Processing.  Minimum human dependence.  Higher data density.  Very cost effective for larger projects particularly in Speed, Accuracy and Density.  Better able to map bare earth elevations in forested or vegetated areas rather than other methods because only a single pulse can be able to reach between trees and ground. Advantages

 High operating cost.  Ineffective during heavy rain, low cloud/mist.  Degraded at high sun angles and reflections.  Unreliable for water depth (<2m) and turbulent waves.  Lack of foliage or vegetation penetration. disadvantage

 Flood Risk Mapping  Oil & Gas exploration surveys  Engineering or Construction surveys  Real Estate Development  Coastal Zone Mapping  Forestry  Undersea Cable Routing  Wreck Detection application

CONCLUSION LIDAR mapping is a maturing technology, and its application are still being detected. There are many ongoing initiatives to identify the areas where technology allows value added products to be generated or where it offers significant cost reduction over traditional survey methods. It is clearly evident that many within the GPS industry are looking at LIDAR as an economical and accurate means of collecting both feature and terrain data, indeed this technology is growing. LIDAR has revolutionized the surveying and mapping world, so it is safe to say that LIDAR will become an important data collection methodology available to the user community.

 Ferguson J. – Vegetation Identification and Classification using LIDAR data – ASPRS/ACSM Rhode Island Workshop, Providence Rhode Island, December  Smith, R.A., West, G.R. – Airborne LIDAR: A Surveying tool for the New Millennium Proceedings, Oceans ‘99 MTS/IEEE, Seattle Washington, September  Berg.R. and Ferguson. J. – Airborne Laser Mapping for Highway Engineering Application ASPRS/AGM 2001, St Louis MS, April REFERENCES