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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004 
Airborne 
Laser 
scanning: 
New 
System 
FAST 1 1L. 
sii | AFFORDABLE 
Radar Se 
Airborne ; E Profilers 
IFSAR 4 — Remote 
sensing 
  
Figure 1: The spectrum of modern mapping tools. The system 
combines the best characteristics across different technologies. 
The sensor choice was a high-quality portable photogrammetric 
camera that is now replaced by high-resolution digital camera, 
with a quality similar to most commercial systems (Mostafa and 
Hutton, 2003). The enabling technology for achieving mapping 
autonomy is the integration of high-accuracy GPS receivers with 
inertial navigation system (INS) that allows tracking the 3D 
motion of the image sensor in space and time. 
In other words, thanks to GPS/INS, a pair of photographs is all 
that is needed to map scenery. The sensor block is light and small 
enough to be hand-held by an operator. Therefore, the installation 
on the helicopter is very quick and a flying mission can be quickly 
executed over any type of terrain. Although precise and quick in 
acquisition, the process of creating elevation models from 
photographs is relatively slow. The approach is therefore less 
suitable in applications where time matters, such as risk 
evaluation. 
Apart from other important benefits listed in Table 1, integrating 
an airborne laser scanner (ALS) into the actual system can 
effectively eliminate this setback. A combination of GPS/INS and 
Lidar data has the potential to provide an almost automated 
generation of the Digital Surface Model close to real-time. Other 
advantages, such as the spectral (intensity) observations, are 
independent of illuminations and are also of great value. 
  
CCD/GPS/INS CCD/ALS/GPS/INS 
  
Autonomous Automation of 3D map generation 
Uniform accuracy 24 hours operation 
Fine details, texture, Intensity image (spectral 
ortho-photo characteristics) 
Fast deployment Quick mapping (day or hours) 
Carrier (helicopter) Uses custom integration and of-the- 
independent shelf sensors — reasonable cost 
  
Table 1: Benefits of laser scanner inclusion 
No matter what the benefits are, the high acquisition cost of 
complete Lidar systems (>1000K USD) cannot be balanced by 
sporadic system use on small surfaces. Moreover, the portability 
of the traditional laser scanning system between different carriers 
is limited because of specific demands (e.g., floor view) and the 
long set-up time. Hence, the cost of maintaining à designated 
system carrier is therefore another prohibiting factor for such type 
of application. An alternative solution by mandating a third-party 
service provider is not suitable due to the need of system 
availability on a short-time notice. Finally, the accuracy in 
mountains, where generally disasters occur, is poor for fixed 
systems due to unfavourable geometry (Favey, 2001; Vallet, 
2002). 
To maintain the benefits of Lidar while keeping the total cost of 
sensor around 100K USD, a combination of a previously 
developed system (Vallet, 2002) with a medium range (~500m) 
Lidar has been undertaken. Moreover, the market release of mid 
format digital cameras in 2002 offered the possibility to create a 
fully digital mapping system of decimetre accuracy at reasonable 
cost. 
The choice of a helicopter as the system carrier is justified by its 
capability to fly close to the ground at low speed. This allows 
capturing photographs in large-scale and provides better flight 
line navigation. In the following, particularities of the system will 
be described together with an analysis of its performance. 
  
Figure 2: The handheld block composed of all the devices: digital 
camera, laser scanner, GPS antenna and IMU. 
2. SYSTEM DESCRIPTION 
Similarly to its former version (Skaloud and Vallet, 2002; Vallet, 
2002), the current system combines several sensors into a single 
block: a digital camera, an inertial measurement unit (IMU), a 
GPS antenna and recently, an airborne laser scanner (Lidar). The 
sensors are rigidly mounted on a light and compact carbon- 
aluminium frame. The block of sensors is handheld and thus offers 
large manoeuvrability while maintaining constant relative