a
TLS and WAAC are new three CCD-line scanners for pho-
togrammetric applications. The cameras with 7500 (TLS)
and 5184 (WAAC) pixels per CCD line allow for recording
the scene with a ground pixel size of 10 cm (TLS) and 1.6 m
(WAAC). Both systems are using GPS and INS sensors for
continuous positioning and attitude determination.
The DPA sensor system is a combination of a photogram-
metric and a multispectral airborne instrument. We want to
discuss more details on the system in the next section. Our
task is to evaluate the system with respect to its potential
and efficiency for photogrammetric-thematic applications.
For that purpose a test flight experiment was carried out
(section 3). Results on georeferencing, image rectification
and multispectral image analysis are presented in section
4. Some expectations on work done next will be given in
the outlook.
2. THE DPA SENSOR SYSTEM
The DPA system is developed by the Daimler-Benz
Aerospace AG (DASA), formerly the MBB GmbH. The cam-
era consists of three panchromatic CCD line arrays for in-
flight stereo imaging (stereo module) and four CCD line
arrays for multispectral imaging using exchangeable filters
(spectral module). The fundamental idea of the system is
to get single-pass stereo coverage and multispectral cover-
age of a scene by recording all seven channels of stereo
and multispectral data simultaneously.
The stereo images are taken with a convergence angle
of +25° between the nadir-looking array and the forward-
looking or backward-looking arrays. All CCDs are Fairchild
sensors with 6 000 detector elements in each line. The
CCD arrays of the stereo module were optically buttoned
using double lenses which gives a wide-angle geometry
with a width of 12 000 pixels for the stereo channels. The
field of view of the spectral and the stereo module are the
same which is obtained by adjusting the focal lengths of
both modules. Some more basic camera data are summa-
rized in table 1.
Table 1: Basic camera parameter
Module Stereo Spectral
Focal length [mm]: 80 40
Line array [pixels/line]: 12000 6000
Data resolution [bit] 8 8
Field of view: +37° +37°
IFOV [mrad]: 0.125 0.250
Convergence angle: +25°
Spectral range [nm]: 515—780 440—525
520—600
610-685
770-890
Connected to the optic module is an INS containing turn
rate gyros and accelerometers. The synchronized registra-
tion of the line image data with the gyro and accelerometer
data is a prerequisite for measuring aircraft motion param-
eters. Processing the inertial data leads to position and
attitude of each image line with a high relative accuracy.
What was missing in DPA so far is the integration with GPS.
The current evaluation of the system was now the occasion
for adding a GPS receiver to the DPA recording system as
indicated in figure 1. Time synchronisation with the GPS
is solved by transmitting pulses of each multiple of 1024
recorded image lines. This time stamps send by the DPA
can be directly registered by the GPS receiver. To be more
flexible in linking further sensors, e.g. a classical aerial
camera, we added a multisensor synchronisation board us-
ing a PC laptop computer.
Another component of the DPA instrument is the stabiliza-
tion platform on which the camera together with the INS is
mounted. Here a SM2000 platform supplied by Carl Zeiss
Jena is used. For data storage of image and supplementary
data an AMPEX High Density Digital Tape (HDDT) recorder
with a data rate of about 110 Mbit per second is used.
The recording system is operated via a standard terminal
using menu input. There is a online display of recorded im-
age on a video screen which allows for checking of image
brightness, camera yaw correction and flight speed with re-
spect to line frequency.
‚The geometric and radiometric calibration of the system is
of general importance for all kind of digital photogrammetric
processing. A renewed geometric calibration of all seven
channels was performed in laboratory by DASA using a
collimator and a precision two-axis angular indexing table.
With that the channels can be co-registated and corrected
for lens distortions. For normalisation of the response of
each channel radiometric calibrations are performed. The
radiometric correction is directly taken into account during
data recoding.
Video monitor
Operating
terminal
m pans cams uam Gu peru nox uer mum uad!
HDDT
recorder
Figure 1: DPA recording system
3. TEST FLIGHT MÜHLACKER-VAIHINGEN
For the experimental evaluation of the DPA a test flight ex-
periment was carried out in 1995. Parameters of this flight
are listed in table 2. This test area Mühlacker-Vaihingen
was chosen because topography and land-use of this area
are well suited for photogrammetric and thematic investi-
gations. The small distance (20 km in northwest direction)
between the test area and Stuttgart (Germany) was benef-
ical for the organisation and field work of this test.
142
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
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