What is LiDAR?
Airborne laser scanning is an active remote sensing method based on LiDAR (Light Detection and Ranging) technology. Airborne laser scanning produces detailed 3D description of the target object. Thus, it is well suitable for measuring forest structure and estimating timber related variables like mean stem volume, basal area and tree size distribution. The laser scanner emits laser pulses, which reflect from the target object. Some of the pulse’s energy is reflected from the object’s surface and some penetrates the object and reflects deeper. By measuring the time distance between the sending of the pulse and the backscattering echo, distance to target object can be calculated. The laser instrument’s precise position is known due to aircraft’s GPS and INS systems. This information combined with the time measurements results in a 3D point cloud with XYZ coordinates of every laser point. We can assume that the first echoes of the point cloud are from the canopy and the last echoes from the ground. The estimation of forest inventory variables is based on variables derived from the classified point clouds.
The vertical accuracy of point observations is 15 – 50 cm depending on terrain, flying height above ground level, used scanning system and the quality of post-processing. In forest inventory, Arbonaut uses low point density data (~1 pulse/m2) which is suitable for area based method. This method is developed for estimating area level (forest compartment or stand, or grid level) results as used by Arbonaut. The wall-to-wall forest inventory information provided by airborne laser scanning is very accurate and has high spatial resolution. LiDAR as sampling can be also used for example to improve accuracy in satellite based inventories when estimating biomass or carbon stock.
The high density data (over10 pulse/m2) allows for individual tree detection, is used for identify dangerous trees that will occur damages to infrastructures like powerlines or railways.
LiDAR based forest methods are improved all the time and research worldwide is very active in this field. For example use of terrestrial LiDAR and ALS with high density (over 3 pulses/m2) for Individual Tree Detection method are progressing all the time and will be used also in commercial production in the future.