Lidar Surveys

Light Detection and Ranging (LIDAR) is an airborne mapping survey method which uses a laser to measure the distance between the aircraft and the ground surface, including buildings and other assets (above ground pipelines, highways, street furniture, power lines, railway tracks), as well as vegetation.

The aircraft also has a GPS (Global Positioning System) to record its position accurately. Commonly the laser takes a reading every 2m to produce a grid of data with an X co-ordinate (eastings), a Y co-ordinate (northings) and a height value.

The video clip below gives an idea of how LIDAR samples are obtained.

The actual laser works by sending out a pulse of light (laser beam). The system measures the time of flight, recoding how long ittakes for the beam to hit a surface and bounce back. Using mirrors the scanner calculates the beams vertical and horizonatal angles, giving actuate X,Y and Z co-ordinates (3D). The poin tis then recorded into a £D visualisation programme. All of this happens in seconds! This process is visualoised below.

Specialist software packages can take these grid files and produce digital terrain maps and present them in a three dimensional view.

This type of information is often used to identify flood risk areas but tends to provide a coarse guide that requires subsequent refinement. Insurance companies and the Environment Agency use this type of data for their initial flood risk assessments.