2.2 LUMOS
LUMOS is a cooperation project funded by German Ministry
of Education and Research.
On the basis of innovative sensor technology which is now
available, a system for the air-supported recording of the traffic
situation was designed, realized, and demonstrated within the
framework of the project (LUMOS 2004).
The whole chain of the system extends from the sensor
technology - including a stabilized platform and image
processing, via the data transmission to the ground - to a traffic
center for the further processing of images in which the
information will be refined with prognosis tools. An open
interface ensures a multi-facetted utilization of the information
by multiple user groups.
The central technological challenges were located in the
software area, ie. in the development of suitable image
processing procedures and the already above mentioned traffic
simulation and prognosis tools. The prognosis plays a key role
and serves the bridging of inevitably occurring time-gaps in the
recording by the airplane. lt thus contributes considerably to
added value and the acceptance of air-supported monitoring.
3. TECHNICAL CONFIGURATION
3.1 Airborne Platforms
Within the two above mentioned projects different airborne
platforms were applied. Their advantages and disadvantages,
the environmental conditions and the user specified traffic
parameters define a compliance matrix.
31.1. Zeppelin
From all available airborne platforms a Zeppelin (ZLT
Friedrichshafen / Germany, Figure 1) was chosen for the
project “Eye in the sky" firstly. The main advantages of the
airship in comparison to helicopters or airplanes are:
= large payloads possible
= highly manoeuvrable
= hovering for several hours
= low flying platform
= low vibrations
Disadvantages of the Zeppelin, including the special ground
based infrastructure needed and expensive flight hours, were
deemed insignificant in light of the overall goals of the project.
Figure 1. Zeppelin on a mobile anchor mast
3.1.2 Airplane
Airplanes are available almost everywhere and allow a quick
access in order to perform test campaigns. DLR used a Grand
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004
Commander 608 for its test flights. For scanning tasks (e.g
road survey) airplanes are well suited.
QS
3.1.3 Helicopter
Helicopters have almost the same positive properties
concerning traffic monitoring as Zeppelins, but the operating
time is significantly lower. For our test campaigns a Bell 206
was applied.
3.2 Camera systems
DLR used its competence on the field of opto-electronic
systems and applied a number of different camera systems in
order to evaluate their parameters and to define configurations
being able to satisfy user specified tasks. A combination of
different sensors seems to be very promising.
3.2.1 Visible Camera
Traffic monitoring requires high quality images. Therefore, a
set of camera parameters was defined in order to fulfil these
requirements.
One of the most important features is the radiometric dynamics
describing the number of bits per pixel per channel. As an
example, an 8 bit camera is able to distinguish between 256
grey values, while a 12 bit sensor can create 4096 different
grey values. The importance of these parameters becomes clear
from looking at aerial photos. Especially in urban areas, very
bright and very dark regions occur within one image due to
totally different reflection properties of the surface (e.g.
specular reflection from windows, drop shadows). An
additional automatic exposure time control is necessary.
The frame rate has to be determined according to the
application. For traffic density, a low frame rate (about 0.2 Hz)
velocity was found to be sufficient, while for car velocity
measurements frame rates in the order of 5 Hz have to be
realized (effectual by common car velocities in cities).
The number of pixels is a compromise between a number of
parameters, e.g. ground resolution, expected movement of the
platform (above all roll and pitch) and provided data transfer
rate.
Several scientific and commercial camera systems were
applied and tested (e.g. Kührt 2001). After defining traffic
density as the main parameter, a commercial camera system
was chosen. Table 1 shows a set of parameters of a typical
camera configuration.
Parameter Value
Detector CCH
Number of pixels 1980 x 1079
Field of view S02
Radiometric dynamics 12 Bit
Frame rate 0.2 Hz
Ground sampling distance, flight height | 0.3 m
1000ft
Swath width 594m
Table 1. Parameters of a typical visible camera configuration
In dependence on the platform, the cameras were mounted
directly on a ground plate (Zeppelin), on shock mounts
(helicopter, Figure 2) or on a stabilizing platform (airplane).
Two main demands had to be fulfilled: firstly, the target area
had to be observed reliably and secondly, the remaining
vibrations must not influence the image quality even for long
exposure times (blurring).
