jerefore an
y corrected
nent and
the image
ard looking
ning a flat
juivalent to
hese strips
the correc-
nal interior
«e images.
necessary
processing
nent with a
uality (e.g.
ences the
ays for the
have been
trically cor-
itude infor-
straightfor-
1 for DEM
the aircraft
N
odels from
1ces of the
neous field
0 measure
| retrieving
lar attitude
ft's tail and
axis. The
INS was placed in the nose of the Do 228. Deviations
between the aeroplane motion and the camera motion
were expected and the measurement were in the order of
a few arcminutes. To compensate for this a gyro block was
mounted directly on the camera base plate. As the attitude
angles given by the INS do not have the necessary accu-
racy, an optical fibre gyro system should be used instead
of the installed INS.
Supplementary measurements with GCPs, for example,
are necessary for the precise determination of camera ori-
entation in the aircraft and of angle offsets.
During the imaging the following attitude data was
recorded: The altitude (GPS and Inertial Navigation Sys-
tem INS of the aircraft), the ground speed (GPS and INS),
the flight path angle (GPS), yaw, pitch and roll angle (INS),
and the angular velocity (3 fibre optical gyros).
The gyro sampling rate was 1 KHz (compared to the INS
witch had a rate of 100 Hz). The possible measurement
range is 0 to 400 degree/s and the resolution 50 degree/h.
The angular are calculated from the velocities by integra-
tion of the angle velocity. The accuracy of the angles is
more precise than the IFOV of a sensor pixel.
The evaluation procedure was explained in [2]. The inte-
gration of the angular velocity leads to an unavoidable drift
rate caused by stochastical velocity errors, which was then
corrected off-line by comparing gyro data and INS data.
The usual drift rate for 1000 recorded lines is 15 pixel.
~~
ees ~
Figure 1 Image of the WAOSS camera
Figure 1 shows an image of the WAOSS camera, which
was recorded during a flight over the city of Berlin. The
image size is 5184x3000 pixels. The ground pixel size is
imxim.
The influence of the aircraft motion is obviously visible in
the left margin of the image. The three columns on the
right hand side of the figure show the roll, pitch and yaw
angular change.The interval for roll angle is [-0.5°,2.4°], for
the pitch [4.0°,4.4°] and for the yaw [86°,96°].
3. CORRECTION OF AIRCRAFT ATTITUDE
INSTABILITIES
With the knowledge of the attitude parameters a correction
of the image strip is possible. The algorithm is processed
in two steps:
1. Determination of the geometric relations in the object
space for each CCD-line pixel results from the disturbed
aeroplane movement
This task is equivalent to ray-tracing from real position and
direction into the digital elevation model (DEM). As the
original DEM is unknown, an ideal DEM is assumed as a
reference plane at z = z;.
The following calculation is made for the object-space.
Geometric relations are as follows:
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996
Xp ideal
\ Xo
t
kN 19) Uf. rea
l o Xq
terrain
y
ui. rT (Xj.Zi) "e
Figure 2 Aircraft attitude instabilities
The intersection point with the surface is
with
Xo current camera location
X; intersection point with reference plane at z,
687
