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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
However, assessment criteria of fusion results obtained from 
different sources have so far only been established in a few 
cases. Therefore, it is necessary to develop quality standards to 
facilitate the comparability of the derived fusion products. Thus, 
the aim of this work was to provide an overview of systems, 
techniques and applications of sensor and data fusion as well as 
to identify algorithms and products for sensor fusion. Moreover, 
it had to be investigated whether such approaches are suitable 
for standardisation. At the same time, the scientific basis for the 
development of a working document for a draft standard for 
requirements for geometric fusion methods had to be 
established. 
This paper results from the standardization of digital 
photogrammetric cameras within Germany (German Institute 
for Standardization DIN, 2007). However, research into fusion 
products needs to be extended with respect to the number of 
different sensor types. This is why a comprehensive research 
into current photogrammetric and remote sensing sensors was 
conducted. The sensors under investigation were systematized 
according to their supporting platform (airborne or spacebome) 
as well as subdivided in active and passive systems to facilitate 
their comparability (see table 1-4). Moreover, the sensor types 
were described and their technical specifications were outlined. 
Concerning the objective - to extract the information relevant 
for standardization - fundamental sensor systems and 
approaches were juxtaposed to aid comparison at the end. 
The paper is organized as follows. The second chapter contains 
an overview of common sensor systems. After a brief 
introduction of fusion principles a number of applications for 
data fusion obtained from different sensors are considered in 
chapter three. Furthermore, some examples of techniques, 
methods and procedures for the fusion of geometric data have 
been identified, correspondingly arranged and differentiated. 
In the fourth chapter some important requirements for fusion 
products are derived. Finally, the paper ends with some 
conclusions and an outlook. 
2. SENSORS 
The tables below show an overview of selected sensors (see 
table 1-4). The sensors are highly sophisticated and deployed 
for production tasks in photogrammetry and remote sensing. 
They can be devided into passive and active sensor systems. 
Active sensors are able to operate at night. Depending on the 
platform (aircraft or satellite) these sensors are classified as 
digital cameras, laser scanners, multi- and hyperspectral 
scanners and radar systems. This list is not exhaustive. However, 
the most relevant sensors from the photogrammetric point of 
view are specified. A more comprehensive overview of high- 
resolution satellite imaging systems can be found in (Jacobson, 
2005). 
airborne 
spacebome 
system 
manufacturer 
system 
manufacturer 
ADS40 
Leica 
Geosystems 
IKONOS 
GeoEye 
DMC 
Intergraph 
QuickBird-2 
Digital Globe 
UltraCam 
X™ 
Microsoft 
Photo 
grammetry 
RapidEye 
RapidEye AG 
Table 1. Passive systems - digital cameras 
airborne 
spacebome 
system 
manufacturer 
system 
manufacturer 
AVIRIS 
NASA 
EnMap 
Kayser- 
Threde, 
GFZ, DLR 
HyMap 
Integr. 
Spectronics 
Landsat 
NASA, USGS 
ARES 
DLR 
GeoEye1 
GeoEye 
CASI 
ITRES 
Table 2. Passive systems - multi- and hyperspectral scanner 
airborne 
system 
manufacturer 
ALTM 
Optech 
ALS50 
Leica 
LMS 
Riegl 
LiteMapper 
IGI 
Table 3. Active systems - laser scanner 
airborne 
spacebome 
system 
manufacture 
r 
system 
manufacture 
r 
E-SAR 
DLR 
A-SAR 
ESA 
ARTINO 
FGAN 
SAR-Lupe 
OHB 
PAMIR 
FHR/FGAN 
TerraS AR-X 
DLR 
AIRSAR 
JPL 
X-SAR/ 
SRTM 
NGA, 
NASA 
EMISAR 
DCRS 
PiSAR 
NICT/JAXA 
RAMSES 
ONERA 
Table 4. Active sensor systems - radar 
2.1 Digital optical high-resolution sensors 
The following approach was taken for quantitative sensor 
classification: High-resolution spacebome sensors have a 
spatial resolution better than 1 m to 2 m, high-resolution 
airborne sensors better than 10 cm to 20 cm. Thus, a resolution 
about ten times higher with reference to the Ground Sample 
Distance (GSD) is assumed. This is related to typical 
applications and sensors deployed in the past. The number of 
measured pixels per image exceeds 100 mega pixels. They have 
a radiometric dynamic of 12 bit to 14 bit and a signal-to-noise 
ratio (SNR) better than 8 bit. Apart from the high-resolution 
panchromatic band, optical airborne and spacebome sensors 
have another four (mostly lower-resolution) multispectral bands. 
2.2 Laserscanner (LIDAR) 
The surface is sampled by a scanning laser beam and the period 
of time between the emission of the laser impulse and the 
receiving of the reflected beams is measured (Time of flight - 
TOF). A more accurate approach is based on evaluation of the 
phase shift between the emitted and received modulated light 
beam. A disadvantage of this approach is the phase unwrapping 
procedure (Wehr, 2005).