TABLE OF CONTENTS LIDAR is an acronym for light detection and ranging, sometimes also referred to as laser altimetry or airborne laser terrain mapping (ALTM). During the last decade, laser scanning turned out to be one of the most promising techniques in photogrammetry. Some photogrammetrists even say that laser scanning has caused a paradigm change in photogrammetry because of its big impact on methods like DTM generation or 3-D city model reconstruction. A LIDAR system basically consists of integration of three technologies, namely, inertial navigation system (INS), LASER, and GPS. LIDARs are classified as active digital sensors in that they emit energy and record a returned signal, and the recorded signal is immediately converted to a digital representation and stored directly onto a computer. As active sensors, they are not dependent on sunlight and can conceivably operate 24 hours a day.
The laser ranging unit contains the laser transmitter and the receiver. The two units are mounted so that the received laser path is the same as the transmitted path. This ensures that the system will detect the target it illuminates. The target size or footprint of the laser is a function of the flying height of the platform and the divergence of the light ray. The divergence of the light thus defines the instantaneous field of view (IFOV) of the sensor. For a spatially coherent beam of laser light, the IFOV is typically between 0.3 mrad to 2 mrad (Wehr and Lohr, 1999). At a flying height of 500m,...
