During assessment a sensor emits laser beams from an aeroplane scanning the area. A single emitted laser has more returns as during its spread it comes into contact with objects of various heights. Some of the laser’s energy is reflected from the nearest object, and the rest goes through and is reflected back later. In a forest, for example, a part of the impulse is reflected by the canopy, the rest goes through until reaching the soil, providing information from the surface as well.
If the sensor is built on the same platform (in this case the aircraft) as a digital camera, then the airborne laser scanning and a digital orthophoto production can be taken simultaneously during one flight.