Managing and processing LIDAR data within GRASS

LIDAR (Light Detection and Ranging) is one of the most recent technologies in surveying and mapping. The LIDAR is based on the combination of three different data collection tools: a laser scanner mounted on an aircraft, a Global Positioning System (GPS) used in phase differential kinematic modality to provide the sensor position and an Inertial Navigation System (INS) to provide the orientation. The laser sends towards the ground an infrared signal, which is reflected back to the sensor. The time employed by the signal, given the aircraft position and attitude, allows us to compute the earth point elevation. In standard conditions, taking into account the flight (speed 200250 km/hour, altitudes 500-2000m) and sensor characteristics (scan angle 10-20 degrees, emission rate 2000 – 50000 pulses per second), the earth elevations are collected within a density of one point every 0.5-3 meters. The technology allows us therefore to obtain very accurate (5-20 cm) and high resolution Digital Surface Models (DSM). For many applications the Digital Terrain Model (DTM) is needed: we have to automatically detect and discard from the previous DSM all the features (buildings, trees, ...) present on the terrain. The elaboration procedure has been implemented within GRASS.