Managing and processing LIDAR data within GRASS

TLDR

LIDAR is a recent technology used for surveying and mapping. LIDAR acquires elevation data by emitting infrared pulses from an aircraft‑mounted laser scanner, using GPS and an inertial navigation system to determine position and orientation, and computing ground elevations from time‑of‑flight measurements, producing DSMs with 5–20 cm accuracy and point densities of 0.5–3 m. The processing workflow has been implemented in GRASS.

Abstract

LIDAR (Light Detection and Ranging) is one of the most recent technologies insurveying and mapping. The LIDAR is based on the combination of three different datacollection 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 anInertial Navigation System (INS) to provide the orientation. The laser sends towards theground an infrared signal, which is reflected back to the sensor. The time employed bythe signal, given the aircraft position and attitude, allows us to compute the earth pointelevation. In standard conditions, taking into account the flight (speed 200- 250 km/hour, altitudes500-2000m) 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 pointevery 0.5-3 meters.The technology allows us therefore to obtain very accurate (5-20 cm) and high resolutionDigital 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 thefeatures (buildings, trees, …) present on the terrain. The elaboration procedure has beenimplemented within GRASS.