LIDAR (Light Detection and Ranging) is a remote sensing method which uses light in the form of a pulsed laser to measure ranges of various distances of the earth. These light pulses along with the other combined data recorded through airborne systems like UAV (Unmanned Aerial Vehicle) can generate 3D information about the shape and surface of the environment. In a LIDAR system, light is emitted from a rapidly firing laser which is like light quickly strobing from a laser light source. The light travels to the ground and reflects off the objects like buildings or trees. The reflected light energy then returns to the LIDAR sensor where it is recorded.
A LIDAR system measures the time it takes for the emitted light to travel to the surface of the ground and returns to the source which is used to measure the distance of the light it traveled. Next, the distance is converted to the elevation through GPS identifiers such as identifying the X,Y,Z location of the light energy and an internal measurement unit (IMU) which provides the orientation of the aerial vehicle in the sky.
A LIDAR technology is a combination of a laser, a scanner, and a specialized GPS receiver. There are two types of LIDAR based on their functionality
1. Airborne LIDAR which is installed on a helicopter or UAV for data collection which is sub-divided into below two.
a. Topographic – uses a near-infrared laser to map the land.
b. Bathymetric – uses water-penetrating green light to measure the seafloor and riverbed elevations.
2. Terrestrial LIDAR- unlike Airborne, Terrestrial LIDAR systems are installed on moving vehicles or tripods on the earth surface for collecting accurate data points for the use of inside or outside of construction sites or building to collect point clouds or various analysis purpose.
Most LIDAR data points will have intensity values recorded by the sensor. Classification of the LIDAR point clouds is an additional processing step where the type of the object is classified. For an example, if the light does reflect off the tree, it will be classified as vegetation.
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