LiDAR Survey

251

LiDAR Survey facilitates the acquisition of data of thousand points over the Earth’s surface within a fraction of a second accurately. LiDAR is one of the most important breakthrough in Optical Remote Sensing technologies. LiDAR means Light Detection And Ranging. LiDAR (Light Detection And Ranging) is the Remote Sensing technology that can find the range and other information about a particular distant object by the means of measuring the properties of scattered lights.

Mechanism of LiDAR Survey:

The LiDAR (Light Detection And Ranging) sensors emit 5,000 to 50,000 laser pulses per second in scanning array. In LiDAR survey, the informations about the objects are determined from the time interval of these LiDAR (Light Detection And Ranging) pulses. The time delay of these transmitted pulses and detected reflected signals are taken as a distance of an object or surface.

In LiDAR Survey, the sensor scans side to side as the aircraft flies over the survey area, by using a pulsed laser beam . It registers or measures 20,000 to 1,00,000 points per second. This raw LiDAR (Light Detection And Ranging) data area very important in building an accurate, high resolution model of the ground and the features present on it.

The LiDAR Surveying involves the simultaneous working of another three technologies. They are as follow:

Laser Scanner for scanning the survey area. Inertial Measurement Unit is there to determine the amount of pitch, roll and heading of the aircraft. This is done by establishing the angular orientation of the LiDAR sensor around their x, y and z axes of the flight. An airborne Global Positioning System works simultaneously with the LiDAR sensor in order to generate the x coordinate, y coordinate and z coordinate of each point.

In LiDAR Survey, the data are collected from individual points over the ground surface. The spacing of these points depend upon the flying height and scan angle.

Types of LiDAR Survey:

Depending on the purpose of the LiDAR Survey, it can be classified into three different categories:

• Bathymetric LiDAR Survey: The main purpose of this LiDAR Survey is to measure the depth of the moderately clear, near shore coastal waters and lakes. This is mainly done from a low altitude aircraft using laser beam.
• Topographic LiDAR Survey: In this LiDAR Survey, elevation data are collected by using laser lights. In this type of LiDAR Survey, the use of GPS is very important for locating the points on the Earth’s surface. This LiDAR technology can collect the data with an accuracy of 15 cm.
• Hydrographic LiDAR Survey: This LiDAR Survey scans the coastal waters, bottom relief of the sea or sea bed with accuracy. The time interval between two successive reflected pulses at different wavelengths are taken as a water depth. One pulses travel through the air water to the water bottom while another one is reflected from the water surface.

Uses of LiDAR Survey:

Now a days this LiDAR Survey, is getting importance in many fields. The field of application of LiDAR Survey comprises the following:

• Geological and seismological studies
• Glacier monitoring
• Measuring the speed of atmospheric wind
• Various application in forestry like: determination of canopy heights, measurement of biomass etc.
• Oceanography
• Defense
• 3-D imaging like DEM (Digital Elevation Model), TIN (Triangular Irregular Network), DTM (Digital Terrain Model) for Terrain Analysis.

Thus, LiDAR Surveying has opened a new horizon in the field of spatial analysis.