LIDAR

LIDAR is the acronym of Light Detection and Ranging. It consists of a laser that scans a target. The target can be a topographic surface, a park, a building, a whole town, the bottom of some kind of water deposit or many pieces of bones. It can be used in scientific applications, in films or in civil Engineering between others. The imagination is the only limit.

The Principles

The LIDAR basically measures the range from the laser device to a target. The range is obtained after transforming the round-trip travel time of the laser pulse from the target to the laser device into a distance. This is obtained after multiplying that time by the speed of light. As the target can be many things, each with its own structure, each point of the target is scanned by the LIDAR. At the end, if the method consists in the recording of discrete returns of the pulse, a point cloud is obtained. If the method consists in the analysis of waveforms, which usually is applied in forested areas, the final product is their structure.

The LIDAR can be mounted on a tripod on the ground, on a truck, on a plane, satellite or any moving or fixed platform. All the system consists of an Inertial Measure Unit (IMU) which provides the orientation (roll, pitch and heading angles) of the laser in the frame of the object where the laser device is mounted. There must be also a GPS (Global Positioning System) antenna tied to the IMU. This configuration together with GPS reference points on the ground allows to geolocate each point of the point cloud.

The positioning error is cm to dm. It is limited by the accuracy of the GPS kinematic positioning and the altitude of the platform. As height increases, the errors in the determination also increase because of the uncertainties in the field of vision (FOV).

It is important to highlight that the system is nothing but a laser without a GPS.

References

Valerie Ussyshkin. 2011. New Airborne Light Detection and Ranging Sensors May Bridge the Niche Applications of Discrete Return and Full Waveform Technologies. SPIE Newsroom. DOI: 10.1117/2.1201105.003734

Jie Shan, Charles K. Toth (Ed.). 2009. Topographic Laser Ranging and Scanning. Principles and Processing. CRC Press.