1. Lidar

How does a lidar work? (1/2)

On the previous page, we explained the schematic structure of a lidar showing the elements laser, telescope, spectograph and photodetector. On this page, we shall try to explain thoroughly how a lidar works. Take a close look at the animation on the right. It shows a lidar which is positioned from above towards a water surface:

1. The laser emits a short flash of light (a laser pulse)
2. The laser pulse is deflected by a mirror in front of the telescope, directing it towards the water surface along the optical axis (i.e., the line of observation) of the telescope
3. A fraction of the light is reflected by the water surface, but most of it is transmitted to the water column
4. The water column itself reflects light. This light is caused by light scattering on water molecules and suspended particles
5. The reflected light is collected by the telescope, analysed by the spectograph (or an optical filter) and then detected with the photodetector.
6. The outcoming signal is displayed in the little box on the upper right corner, whereby the x-axis shows the elapsed time (in relative units) from the moment the laser pulse was emitted, and the y-axis shows the intensity of the light detected.