m as
GPS
1024
| DPA
more
aerial
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rected
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Table 2: Parameters of the test flight Mühlacker-Vaihingen
Area: 4.5 km x 7 km
Flying height above ground: 2300 m
Velocity of aircraft: 70 m/s
Scan frequency: 235 Hz
Ground pixel size of
stereo images: 0.30 m
multispectral images: 0.60 m
Date of flight: 26.07.1995
The test flight was performed together with Kirchner and
Wolf Consult, Hildesheim. An aircraft equipped for carry-
ing two camera systems simultaneously was used which
allowed for taking DPA images and aerial images with the
RMK TOP 15 during the same flight. For our investiga-
tions this gives us the opportunity to compare the quality of
photogrammetric restitution using the DPA with the results
found by the classical photogrammetric techniques using
aerial images. For having ground truth data about 200 sig-
nalized points have been spread out in the test region. For
that purpose white PVC-plates have been used and white
paintings are drawn on ground with a size of 1 x 1 m?. The
scene is captured by three strips flown in east-west direc-
tion and three strips in north-south direction. The neigh-
bouring strips have a side overlap of 60 percent.
The scheme for processing the DPA data of this flight exper-
iment is shown in figure 2. Computations with the 1 Hz GPS
data are carried out using standard software packages. Po-
sition and attitude determination from the INS data is solved
within the DPA system which also serves for HDDT conver-
sion of the recorded data. The other two boxes in figure 2
deal with GPS-INS integration and image rectification. For
these tasks software has been developed. The results of
this processes are presented in the next section.
(=) (a) (= ) (os. )
aus
RMK
Time Stamp DPA ape DPA
Synchroni-
Y sation System
conl
oordinates
GPS ad A Time Stamp | HDDT
Processing Y
Camera GPS Time HDDT
Position y Conversion
Original
GPS-INS mí an
Ÿ
INS Dat
Integration SD
| > Image
Camera Orientation Rectification
(without DTM)
fr nr nr gon mn ps fs gon ton pean pp ts on nts nt we nem — e— nn
Rectified Images
Y y i
DTMs.
Digital ; GIS,
rthoi y
Photogrammetric ono rap es Thematic
Stations Mapping Mapping
Figure 2: DPA test flight processing scheme
The intersecting line between DPA specific data processing
with the upgrade of raw data and the application depen-
dent further use of processed data is currently drawn at
the end of the image rectification process. The rectified
images can be introduced into Digital Photogrammetric
143
Workstations where stereo viewing supports the measure-
ment processes. Stereo impression is quite bad with the
directly recorded image data even though a stabilized plat-
form is used. The rectified image data can be processed
further with line triangulation modules for 3D recovery or
with DTM packages, for example, the MOMS algorithms
(Fritsch et al., 1995) for DTM reconstruction. The geo-
referenced multispectral and panchromatic images are of
increasing importance as a source for GIS. Our interest is
in topographic and thematic mapping with the DPA data
where a lot of research has to be done in fusing the data
and the evaluation and interpretation techniques to exploit
the potential of the DPA sensor.
4. PHOTOGRAMMETRIC-THEMATIC PROCESSING
In this section we present experiences with georeferencing
and image rectification of DPA stereo images and discuss
first results obtained by multispectral analysis of the spec-
tral DPA channels.
4.1 GPS-INS Integration
The INS is required to measure the high frequency transla-
tional and rotational motion parameters of the airborne sen-
sor. Because the optic module is put on a stabilized plat-
form only angular movements are recorded which are not
compensated by the platform. A plot of the attitude rates is
shown in figure 3. Quite easy to see are a few sharp peaks
with an amplitude of 0.015? at 235 Hz or 3.5? /sec. This high
changes of the attitudes can only be explained by rotational
aircraft motion passing over the compensation interval (of
around £5°) in which the platform is fully operational.
Roll [degree/ine]
Pitch [degree/ine]
Figure 3: Attitude rates (roll and pitch) of one strip
For georeferencing of airborne sensors the GPS-INS inte-
gration is considered to be the most powerful technique.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
