lir direction,
: the interband
; for instance
the combina-
lired 9 bands
r and aft
:lly regis-
iplied off-line
;ize and for
The module
i be tilted
that a compact
to the total
'indow in the
atory air-
.ESAR camera
separation for
minimized by
void the intro-
room scan prin-
he object
a for sea ob-
em, the dy-
ld be deter-
ance, the
bserved, the
of the ima-
ptics and the
ty, band width,
addition the
role. For land
the required
lution of 0.5
of the mea-
emperature
calibration in
ontrol would
ents for the
he same
ervation
400-420 nm
435-455 nm
510-530 nm
555-575 nm
620-640 nm
675-695 nm
770-800 nm
990-1050 nm
ed twice)
£ 0,05% for
all bands
10 and 20 m
5.7°.
Fig. 1 Selection of spectral bands for land and
sea observation by CAESAR.
Fig. 2 CAESAR CCD camera module
The main components are the standard
objective, the spectral separation,
bandfilters and CCD detectors and the
selector electronics.
From a market survey executed in 1982, three manu
facturers of CCD's with 1728 detector elements were
selected on basis of a set of primary criteria. A
dedicated CCD testbench has been developed by the
TPD. A detailed test programme has been executed
with respect to the following characteristics: dark
current (non-uniformity and temperature dependence),
detector sensitivity, radiometric linearity and dy
namic range, detector cross- talk, efficiency of
signal conversion and charge transport. Finally one
type of CCD was selected.
DATA ACQUISITION AND REGISTRATION
The NLR has developed a family of airborne analog to
digital data conversion systems for different types
of sensors like Side-looking Airborne Radar, Infra
red line Scanner and Video camera. Based on the
approach of a dedicated analog to digital convertor
combined with a standardized programmable data for
matter and an airborne high bit rate recording system,
Fig. 3 Pushbroom scanning for land observation
with 3 co-registered (central) channels
of the modules; for sea observation all
9 channels (3x3 co-registered) are used.
for CAESAR the multichannel convertor "CEDIG" has
been developed.
The maximum input data rate for the HBR has been
upgraded to 8.4 Mbits per sec. The CEDIG system is
programmable with respect to the number of pixels
per scanline, the number of bits per pixel and the
integration time. The number of samples per line is
either 1280 or 1792. Electronic roll correction is
realized by positioning the 1728 pixels within the
1792 samples or by selection of 1280 pixels from the
1728 measurements.
By changing the integration time the number of scan
lines per sec with corresponding along-track spatial
resolutions can be changed stepwise. In such a way
trade-offs are possible between intensity resolu
tion, spatial resolution, swath width and number of
channels.
REALISATION AND FLIGHT TESTING
Figure 4 shows the configuration of the CAESAR sensor
system. Three identical CCD camera modules are moun
ted on a common base plate and are aligned in paral
lel in the optical laboratory of the TPD. The three
modules are protected by means of a box. This down
looking box is mounted in a support structure. The
baseplate can be adjusted at the selected tilt
angle. Beside the three modules, the forward-looking
module is mounted within the support structure. The
off-nadir direction can be varied with a number of
discrete steps.
The internal temperature of both modules can be
maintained at a nominal level by means of a flow of
dry cooled air. This is required in case of opera
tions in tropical regions.
The electronics, the inertial navigation platform
and the high density recorder are mounted in remo
vable racks inside the aircraft. The first in-flight
tests have been executed in 1984 for initial perfor
mance testing of the integrated system and for the
generation of image data required for the develop
ment and testing of the dedicated system correction
(preprocessing) software. Figure 5 presents an
example of one of the first images. No geometric and
radiometric corrections have been applied, except
the real time roll correction. After the first in
flight tests a series of environmental tests have
been executed, like vibration tests, temperature and
electromagnetic interference tests. Some mechanical
improvements of the support structure and modifica-
