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DEVELOPMENT AND EXPERIENCES WITH A FULLY-DIGITAL HANDHELD MAPPING 
SYSTEM OPERATED FROM A HELICOPTER 
J. Vallet * ", J. Skaloud ° 
* EPFL, Laboratory of Photogrammetry, CH-1015 Lausanne, Switzerland — julien.vallet@a3.epfl.ch 
° EPFL, Laboratory of Topometry, CH-1015 Lausanne, Switzerland — jan.skaloud@epfl.ch 
Commission I, WG I/5 
KEY WORDS: Photogrammetry, Disaster, Mapping, CCD, GPS/INS, LiDAR, Integration, Acquisition. 
ABSTRACT: 
This paper presents a self-contained, light and flexible mapping system that can be quickly deployed into inaccessible areas. Although 
designed to measure wind-transported snow volumes and the avalanche mass balance over an experimental site, the system is suitable to 
any large-scale 3-D terrain mapping. The system is comprised of supporting electronics that is loosely linked to a light but ridged sensor 
block containing digital camera, Lidar, an IMU and a GPS antenna. The relatively small size and weight of the sensor block permits 
manual pointing of the camera and the Lidar either towards the mountain face or the valley bottom. Such hand-held steering allows 
mapping of the avalanche/land slides release and deposit zones during the same flight with an optimal geometry. At the same time it 
dampens the engine-induced vibrations on the sensors. The installation time of the system in a helicopter is less than 15 minutes and its 
re-installation does not require new calibration. The exterior orientation (EO) parameters of the camera and laser are determined directly 
by GPS/IMU integration. Optionally, the orientation performance of the navigation solution may be improved by integrating the data 
from the second GPS antenna placed on the helicopter tail. Once the system is calibrated (once per sensor assemblage) and with EO 
determined for both sensors, an automated DTM and orthophoto generation can be achieved. The practical experience with 
CCD/GPS/INS has demonstrated a mapping accuracy of 10cm and 15cm in the horizontally and vertically, respectively. The 
performance of recently added Lidar 1s under evaluations. 
1. INTRODUCTION 
1.1 Motivations 
Switzerland is making an effort to improve its preventative 
measures against natural disasters. In the cycle of integrated risk 
management, the steps of intervention and reconstruction 
following a disaster are studied, and then the phase of rebuilding 
is followed by implantation of prevention methods. Each of these 
phases attempts to reduce certain risks and impact of a natural 
catastrophe. 
In this context, observation methods for certain phenomena and 
their impact on the land and infrastructure are essential in order to 
optimize certain processes and to make correct decisions. 
Surveying instruments, photogrammetry and, more recently, laser 
and radar systems have been integrated into surveillance 
platforms in an effort to examine zones which are at particularly 
high risk. Including these observation methods in the process of 
integrated risk management demands systems of particularly high 
performance. For example, it is essential that the transfer of data 
(motion, coordinates, image, digital terrain model) occur quickly 
and without delay in order to ensure the smooth continuation of 
the entire data collection process. 
The objective of this research is to produce a cartographic system 
that can be rapidly deployed in the event of a catastrophe. This 
concept of near real-time cartography is very important for those 
attempting to intervene during such events. 
1.2 System Requirements 
The designed system aims to fulfil the following requirements: 
e Fast set-up and availability (minutes or hours) 
° Relative independence from a particular carrier 
e Possibility to map near vertical (mountain faces) and 
horizontal (valley bottoms) features during the same 
flight with uniform accuracy 
° High relative and absolute mapping accuracy («20cm) 
. No assistance of ground control points 
e Fast delivery time for DTM and orthophoto generation 
(few hours after flight) 
1.3 Evolution of a System Concept 
The modern mapping and remote sensing tools can be classified 
according to three basic criteria: 
e. Precision, resolution and sensitivity 
e Deployment speed, mapping speed and product delivery 
turn-around time 
e. Instrumentation cost and carrier dependence 
The trade-off between these conditions gave a rise to different 
systems as depicted in Figure 1. The development of the EPFL 
system called HELIMAP started in 1999 as a response to the need 
of SLF-Davos (Swiss Federal Institute for Snow and Avalanche 
Research) in mapping avalanches and snow transport (Issler, 
1999). The emphasis was placed on high resolution and accuracy 
(10-15cm), low cost and system portability (i.e. independence 
from a carrier, Skaloud and Vallet, 2002).