LIDAR Light Detection and Ranging Technology

LIDAR Light Detection and Ranging Technology

LIDAR Light detection and ranging is a method of determining the topography of the surface using a laser These pulses generated are recorded which provide precise threedimensional information about the surface Today various platform LIDAR is available in the market and those are chosen based on the project requirement Eg terrestrial LIDAR which is fixed in ground airborne LIDAR which is placed on a flying platform like an airplane or helicopter and space borne Laser which is fixed on satellite platforms Two types of LIDAR are available topographic and bathymetric Topographic LIDAR use near infrared laser whereas bathymetric LIDAR us green light which penetrate the water

The use of airborne laser LIDAR for measuring the depth of near shore coastal waters and lakes from an aircraft is getting more popular in surveying industry The demand for faster and cheaper coastline survey can be replaced by using airborne LIDAR technology The Airborne LIDAR bathymetry was successfully tested by US Canada and Australia in the early 1970s The system built by Canadian Hydrographic Service CHS in 1986 the LARSEN 500 system was the first operational airborne LIDAR bathymetry system

Airborne LIDAR bathymetry has proven to be more accurate cost effective efficient and fast method of collecting shallow water bathymetry data than the sonar technology which is less efficient and hard to operate in many cases The airborne laser bathymetry involves the pulse laser transmitter which emits green and infrared beams The wave length of green laser is 532 nm which can penetrate coastal water with less attenuation and can be used for coastal bottom detection The infrared IR cannot penetrate the water and can be used for sea surface detection The bathymetry sensors consist of four major components the GPS receiver which records the aircraft position the inertial measurement unit IMU which gives the roll pitch and yaw of the aircraft the laser scanner which emits the signal and the receiver sensor which read the returning signal The LIDAR system can record the accurate measurements by knowing the position and orientation of all these components These sensors can measure thousands of points per seconds

The transmitted laser pulse from the aircraft partially reflected from the water surface and the seabed back to the receiver By recording the time taken from the laser to reach the surface and back to the receiver and speed of the light in air and in water the distance to the sea surface and sea bed can be calculated This information is used to calculate the water depth The bathymetric LIDAR system also includes RGB cameras which acquire better color photo which is used as a quality check tool in identification of bathymetric features and aids to navigation Airborne LIDAR bathymetry has various advantages over other traditional water borne surveying techniques It has tendency to perform survey quickly efficiently within small operational window This can cover a very large area and all those areas where it would be difficult to survey using traditional surveying methods The ability of the airborne LIDAR to operate from the air gives the surveyor a flexibility that survey vessel surveyors could hardly imagine The modern airborne LIDAR now comes with oblique digital photography which can be merged with point cloud These georeferenced images are used during the validation process

There are numerous limitations of an airborne LIDAR bathymetry system The maximum depth the laser can penetrate depends on the clarity of water The maximum surveyable depths depend on several systems used and the environment condition The green laser penetrates and travel maximum depth if the water is clear water The maximum surveyable depths ranges from 50 meters in clean water to less than 10 meters in murky water The use of airborne LIDAR system is not appropriate for small target detection The spatial resolution obtained from the airborne LIDAR is not as good as for modern h

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