STEREO PROCESSING WITH ATTITUDE-DISTURBED IMAGE DATA
Anko Börner, Ralf Reulke, Martin Scheele, Thomas Terzibaschian
German Aerospace Research Establishment (DLR)
Institute for Space Sensor Technology
Rudower Chaussee 5, D-12484 Berlin,
Tel.: (+49) 30 69545518, Fax: (+49) 30 69545512
e-mail: Ralf.Reulke@dlr.de
KEY WORDS: remote sensing, stereo camera, CCD line scanner,DEM, attitude measurement
ABSTRACT
We are now on an intersection point of three developments leading to a new quality of stereo photogrammetry:
- development of metric large CCD-lines,
- highly accuracy attitude measurements and
- nearly unlimited processing and storage capabilities.
In this paper approaches and algorithms for 3-D processing of attitude-disturbed images are published. Therefore an
optical fibre gyro system was installed to overcome the problems of attitude inaccuracy.
Using attitude and camera calibration data the image strips can be geometrically corrected. The geometrically corrected
images are a necessary data product for further 3-D processing and allow also a simple coordinate measurement and
the generation of digital elevation models (DEM).
1. INTRODUCTION
The Wide-Angle Optoelectronic Stereo Scanner (WAOSS)
is one of the remote sensing instruments of the Mars-96
orbiter. The basic scientific objectives are the global imag-
ing of Mars' surface and atmosphere for the investigation
of meteorological, climatological and related surface phe-
nomena and changes.
These special mission objectives, a highly elliptical orbit
and the camera design require a very flexible concept of
sensor-signal processing and evaluation algorithms. The
development and tests of algorithms with current data are
necessary and for this purpose an airborne-sample of the
future satellite camera was manufactured and flown (see
[1]).
The use of WAOSS on board aeroplanes instead of satel-
lites causes changes in measurement and evaluation pro-
cedures, particularly the attitude instabilities of the aircraft
(roll, yaw, pitch, ground speed and altitude variation) which
are much more pronounced than those of the satellite. A
stabilizing aircraft platform was not used for reasons of
simplicity, size, weight and funding.
Concerning the data evaluation of an image strip recorded
from an airborne camera the principal disadvantage of a
line sensor is that the attitude parameters are necessary
for each row in the image.
Due to the inaccuracy of the inertial navigation system
(INS) conventional photogrammetric methods use addi-
tional control points on the Earth's surface to improve the
attitude parameters. The application of this approach to
images from a line sensor needs a model for the flight path
and an iterative improvement for the attitude parameters
with additional ground control points (GCP) (see [5]).
The algorithms described in this paper requires no or only
a small number of GCPs. Therefore an optical fibre gyro
system was installed to overcome the problems of attitude
inaccuracy. This measurement approach makes a platform
unnecessary.
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996
Using attitude and camera calibration data the image
strips of the nadir, the backward and the forward looking
line can be geometrically corrected assuming a flat
underlying surface. This image product is equivalent to
an undisturbed flight over a flat surface. If these strips
are processed on the same mean flight path the correc-
tion procedure is equivalent to the conventional interior
and exterior orientation and gives epipolar-like images.
The geometrically corrected images are a necessary
preprocessed data product for further 3-D processing
and allow also a simple coordinate measurement with a
photogrammetric workstation for example.
This procedure also increases the image quality (e.g.
streets become straight lines) and influences the
number of matched points. Two different ways for the
generation of digital elevation models (DEM) have been
analysed:
- matching and DEM generation with geometrically cor-
rected images
- matching and DEM generation using the attitude infor-
mation directly.
The independence of additional GCPs and straightfor-
ward algorithms make an on-line approach for DEM
generation or DEM improvement on board the aircraft
possible.
2. ATTITUDE DETERMINATION
Known methods are able to evaluate 3-D models from
line scanner data only if the attitude disturbances of the
aircraft are small compared with the instantaneous field
of view (IFOV) of the camera (e.g.[3]).
To overcome this problem it is necessary to measure
and incorporate exact attitude data in the retrieving
algorithm.This concerns especially the angular attitude
data.
The camera was rigidly mounted in the aircraft's tail and
the aircraft axis coincided with the camera axis. The
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