Ts
nd
Ta
a;
or
in
ill
ar
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV , Part B6. Istanbul 2004
arrays with geometric characteristics similar to a film camera,
and line scanners using linear arrays with a different geometry.
Five different digital sensors are considered here, two multi-line
scanners (ADS40, HRSC), two multi-lens frame cameras
(DMC, UltraCamD) and one-lens camera (DSS).
The Leica Geosystems ADS40 Airborne Digital Sensor was
developed in co-operation with the German Aerospace Centre
(DLR) in Berlin using an extended three-line concept. A verti-
cal panchromatic (465 — 680 nm) image is obtained using two
linear CCDs each having 12000 6.5 um large pixels; an offset
of 3.25 um yields a useable length of 24000x3.25 jim = 78 mm.
A lens angle of 64? translates into a focal length of 62.8 mm.
The camera achieves stereo capability by means of two
additional single linear CCDs taking panchromatic images, one
looking forward 28.4? and one looking backward 14.29, the
look angle difference of 42.6? corresponds to that of a normal
angle aerial film camera with c = 305 mm. The data transfer
rate from the CCDs is up to 800 Hz; combining this with a
(minimum) aircraft speed of 370 km/h = 200 knots = 102.8
m/sec yields a (smallest) pixel size on the ground of 15x15 ¢cm?,
a (minimum) swath width of 3600 m, a (lowest) flying height
above ground of 2880 m (9449") and a (largest) image scale of 1
in 46154. Smaller ground pixel sizes and larger image scales
can be achieved by using slower aircraft; it has been reported
that one owner uses the camera routinely at a flying height of
1500 m yielding an image scale of 1 in 30769 and a swath
width of 2.4 km. In addition to the panchromatic arrays, three
linear arrays located at 14.2? off nadir are used to capture blue
(430 — 490 nm), green (535 — 585 nm) and red (610 — 660 nm)
images with perfect co-registration. One near infrared line (835
— 885 nm) located at 2? off nadir is also provided.
The HRCS High Resolution Stereo Camera was originally de-
veloped for (failed) Mars missions by the Institute of Planetary
Exploration of the German Aerospace Centre DLR in Berlin-
Adlershof. First experiments were carried out with an airborne
version (HRSC-A) in early 1997; their success prompted the
further development (HRSC-AX). A vertical panchromatic (520
— 760 nm) image is obtained using one linear CCD having
12000 6.5 um large pixels yielding a useable length of 78 mm.
A focal length of 150 mm translates into lens angle of 29°. The
camera achieves stereo capability by means of two additional
single linear CCDs taking panchromatic images, one looking
forward 20.5? and one looking backward 20.5°, the look angle
difference of 41° corresponds to that of a normal angle aerial
film camera with ¢ = 305 mm. A shortest exposure time of 0.6
msec and an aircraft speed of 300 km/h = 162 knots = 83.3
m/sec yield a (smallest) pixel size on the ground of 5:15 cm?, a
(minimum) swath width of 600 m, a (lowest) flying height
above ground of 1153 m (3786') and a (largest) image scale of 1
in 7692. In addition to the panchromatic arrays, two linear
arrays located at +2.3° and -2.3° off nadir are used to capture
green (530 — 570 nm) and red (635 — 685 nm), and two linear
arrays located at +4.6° and -4.6° off nadir are used to capture
blue (450 — 510 nm), and near infrared (770 — 810 nm) images.
The camera includes two further panchromatic arrays located at
* 12.0? and at -12.0? enabling 5-line stereo evaluation in critical
areas.
The DMC from Z/I Imaging uses four CCD arrays of 7168x
4096 pixels? (probably Philips Icam28, 111x86 mn», pixel size
12x12 jum?, readout time 2 sec/frame, 12 bit radiometric reso-
lution) to take high-resolution panchromatic images; the four
images with slightly diverging optical axes are afterwards com-
211
bined to one image with 13824x7680 pixels? (Fig. 1). The lar-
ger dimension of the 166x92 mm? image area is oriented per-
pendicular to the flight direction. A focal length c = 120 mm
results in a field of view of 69.3° perpendicular to and of 42° in
flying direction, the latter corresponds to that of a normal angle
aerial film camera with c = 305 mm. A maximum frame rate of
two images per second allows extremely large image scales;
hence, rather small pixels can be obtained. In addition to the
four panchromatic cameras, four cameras with arrays of
3072x2046 pixels capture blue (400 — 580 nm ?), green (500 -
650 nm ?), red (590 — 675 nm ?) and near infrared (675 — 850
nm ?) images using a focal length of c = 25 mm. Hence, the
pixel size ratio pan to colour amounts to 1 to 4.75.
The UltraCamD from Vexcel Imaging uses nine CCD arrays of
4008x2672 pixel? (pixel size 9x9 un^, readout time 1.3 sec per
frame, 12 bit radiometric resolution) to take high-resolution
“synoptic” panchromatic images through four lenses in flight
direction with slightly diverging axes and small time delays; the
images are afterwards combined to one image with 11500x7500
pixels? (Fig. 2). The larger dimension of the 103.5x67.5 mm?
image area is oriented perpendicular to the flight direction. A
focal length ¢ = 100 mm results in a field of view of 55°
perpendicular to and of 37° in flying direction. A maximum
frame rate of 1.3 images per second allows extremely large
image scales; hence, rather small pixels can be obtained. In
addition to the four panchromatic cameras, four cameras with
arrays of 4008x2672 pixels capture blue, green, red and near
infrared images using a focal length of c = 28 mm.
The DSS Digital Sensor System from Applanix is a ready-to-
use, directly geo-referenced, medium format, airborne digital
sensor using a single three-colour CCD array of 4077x4092
pixels?. À focal length c = 55 mm (optional 35 mm) results in a
field of view of 37°, the latter nearly corresponds to that of a
normal angle aerial film camera with c = 305 mm. The DSS is
available as true-colour or as false-colour version. In the latter
case, the filters integrated into the sensor form a basic 2x2 ma-
trix: one element sees infrared (720 — 920 nm) radiation, two
elements see green (510 — 600 nm) and infrared radiation and
one element sees red (600 — 720 nm) and infrared radiation.
4. PROJECT AREA
The extended area of the confluence of the Elbe and Mulde
rivers was selected as project area. This area was subject to
extended flooding in August 2002 resulting from almost con-
current extremely high water levels of both rivers. The damages
to valuable vegetation partly non-native to Germany were high.
At this time the lack of available digital terrain data with
sufficient point density and elevation accuracy to predict the
effects of further water level rises and of dam breakages be-
came apparent. Expectations to gain financial support for the
project from the state government of Saxony-Anhalt were not
fulfilled.
This area is part of the UNESCO biosphere Mid-Elbe which
contains the largest floodplain forest in central Europe. Bio-
sphere reserves are large-scale, representative sites of natural
and cultural landscapes. They are not simply schemes to protect
the environment but model concepts of conservation, de-
velopment and management are developed under the UNESCO
Man-and-Biosphere program.
