A discussion over the importance of lidar in mapping industry

LIDAR is becoming an important mapping tool that is finding a growing audience in GIS. Here you will know the principles of LIDAR and the capabilities that this new technology offers the mapping professional. LIDAR systems will be described and accuracy issues will be discussed. Examples of LIDAR projects will be presented to see how terrain detail can be extracted from LIDAR measurements. 

LIDAR is a relatively new technological tool that can be used to accurately georeference terrain features. LIDAR is an acronym for LIght Detection And Ranging and in some literature it is referred to as laser altimetry. While the system is new, the underlying technologies that comprise a system have been around for a number of years. A LIDAR system (see figure 1) is composed of a laser scanning system, global positioning system (GPS), and an inertial measuring unit (IMU).

Lasers (Light Amplification by Stimulated Emission of Radiation) have been used for years in the geospatial sciences. The laser basically consists of an emitting diode that produces a light source at a very specific frequency. The signal is sent towards the earth where it is reflected off a feature back towards the aircraft. A receiver then captures the return pulse. Using accurate timing, the distance to the feature can be measured. By knowing the speed of light and the time the signal takes to travel from the aircraft to the object can back to the aircraft, the distance can be computed using the basic relationship
                                                  D = v/t
where D is the distance from the aircraft to the object (this is one-half the total distance that the laser signal actually traveled), v is the velocity or speed of light, and t is the time between emitting and receiving a particular signal.