Lidar (“Light Detection and Ranging” or “Laser Imaging, Detection and Ranging”) was developed in the early 1960s. It was quickly adopted by researchers, from archaeologists to atmospheric scientists. The article “LIDAR AND LOST CITIES IN CENTRAL AMERICA” posted on Past Horizons May 12 2013 (Past Horizons, 2013) shown the favourite of the archaeologist for Lidar technology. It not only proved that Lidar was a useful tool to allow archaeologists to “see” through the forest canopy to the ground surface and reveal the evidence of ancient settlements or human-engineered landscapes, but also stated that researchers in this team championed the use of Lidar as a scientific revolution that would fundamentally change the way that archaeologists do fieldwork. Without a doubt, Lidar had become a popular technology for the direct acquisition of topographic information.
Now, the Lidar system classifies into three main areas based on their platform: Airborne Lidar System (ALS) – aircraft or satellite, Mobile Lidar System (MLS) – moving vessel or vehicle and Terrestrial Lidar System (TLS) – the ground. The characteristic of ALS and TLS makes them only be able to view the target area in long-range resolution and point view resolution. However, for the complex spatially urban environments usually requires data collection from multiple viewpoints. Hence, Mobile Lidar System is considered to fill the gap i.e. short range resolution.
As a new generation of Lidar technology, Mobile Lidar System attracts many researchers from government agencies, companies and universities to study its capability, improvements and applications. Several vehicle based laser scanning systems have been built in recent years (e.g. Talaya et al.2004, Grinstead et al.2005, Pfaff et al. 2007, Kremer & Hunter 2007, Barber et al 2008).The basic principle of MLS is similar to the principle of ALS. The main challenge to transfer the MLS data into a ground coordinates is to work out the mathematic relationships between different sensors’ coordinates systems, such as the most critical errors -- boresight errors which are the angular deviations between the sensors and leverl-arm error that are the offsets between origins of the coordinates systems of sensors as the following figure shown. The errors are variable due to vary of sensor type and the different system structure design. Boresight errors can be introduced from re-assembling the equipment after shipment. Thus, it is necessary to do a boresight calibration survey prior to or after the data acquisition so that boresight errors could be eliminated in the post-processing.