The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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At VITO, the Pegasus project was proposed as early as 2000, 
aiming to use a High Altitude Long Endurance (HALE) UAV 
for remote sensing. The UAV, called Mercator, is related to the 
QinetiQ Zephyr systems (Fransaer, 2004). 
In May 2007, the US Defence Advanced Research Projects 
Agency (DARPA) announced the VULTURE Air Vehicle 
Program. This is aimed at developing a heavier-that-air 
platform that can maintain an airborne payload on station for 
an uninterrupted period of over 5 years. In April 2008, first 
phase contracts were awarded to three contractor teams headed 
by Aurora Flight Sciences, Boeing and Lockheed Martin. 
(DARPA, 2008) 
3. REMOTE SENSING INSTRUMENTS 
Low altitude UAVs are used to carry light-weight instruments. 
In most cases, these consist of off-the-shelf component such as 
consumer digital cameras (Eisenbeiss, 2006; Haarbrink, 2007, 
Martinez Rubio, 2005)). At low altitude, it is possible to 
achieve very high resolution, and it has been shown that 
consumer grade SLR cameras offer sufficient precision and 
stability to allow photogrammetric extraction of information 
(Shortis, 2006). Other instruments include (combinations of) 
imaging systems covering visible to thermal spectrum, with 
multi- or hyperspectral sampling, miniature RADAR, passive 
microwave radiometers, and LiDARs (Vierling, 2006; Sugiura, 
2005; Sugiura, 2007; Martinez-de Dios, 2006; Archer, 2004). 
On the other hand, UAVs are also used as a test bed for new 
instruments or integration of instruments (Colomina, 2007) 
This is of significant importance, as it allows research groups 
that specialize in instrument design to test prototypes on a 
regular basis. 
At VITO, a high resolution wide swath digital camera is under 
development for flight on Mercator within the Pegasus project. 
This camera uses extremely light-weight subsystems to reduce 
the total mass to less than 2.5 kg and still generate 30 cm 
ground sampling distance from 18 km altitude (Delaure, 2007). 
In short, UAVs have carried instruments that cover the whole 
range of the spectrum that remote sensing has addressed. 
Usually, however, it is not possible to carry the instruments 
that have been conceived for larger manned platforms, so 
innovative solutions have been found. 
4. APPLICATIONS 
Many remote sensing applications have benefited from the use 
of UAVs. In most cases, this was due to the cost of the mission, 
the need for rapid response or the fact that observations need to 
be carried out in an environment that may be harmful or 
dangerous to an aircrew. 
A striking example is the adoption of remote sensing using 
UAVs in archaeology (£abuk, 2007; Eisenbeiss, 2006; 
Martinez Rubio, 2005). The main purpose is to document 
archaeological sites, and to provide ‘a bigger picture’. The 
accuracy requirements are not very high, although it has been 
shown that e.g.; elevation accuracy using a helicopter UAV and 
a consumer digital cameras (Canon EOS-D60) yields elevation 
models that are comparable to ground laser scanner 
measurements. 
Vegetation monitoring has also been successfully done using 
UAVs. A HALE UAV, Pathfinder Plus was used to 
demonstrate this on a coffee plantation in Hawaii (Herwitz, 
2004); others have studied rangelands (Rango, 2006), and in 
Japan these systems are considered to be an integral part of 
farm equipment (being catalogued as ‘flying ploughs’; 
Newcombe, 2007). 
Rapid response imaging using UAVs has received a lot of 
attention as well. This has been demonstrated for road accident 
simulations (Haarbrink, 2006) and in many cases of forest fire 
monitoring (Restas, 2006; Martinez-de Dios, 2006; Casbeer, 
2006). UAVs have also been proposed as platforms to monitor 
volcanoes (Buongiomo, 2005). 
A final example of the flexibility of UAVs is their use in traffic 
monitoring (Puri, 2007; Doherty, 2004) 
5. CONCLUSIONS AND OUTLOOK 
The number of UAV systems used in remote sensing and 
mapping have soared in the past four years. Coming in almost 
all possible forms and sizes, they have flown a multitude of 
remote sensing instruments for many applications. Much of 
this work is still in the research phase, and there are few “off- 
the-shelf’ systems that offer complete solutions to a user. 
UAVs have given remote sensing a new appeal for scientists, 
who will now be able to conduct research in a much more 
flexible way. It is easy to foresee that, when all aviation 
regulations have been adapted to include these systems into the 
general airspace, UAVs will rapidly become the preferred 
platform for development of remote sensing instruments and 
applications. 
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