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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004
3. CAMERA OPERATION
The camera operation of a frame based digital camera like
the DMC is very similar to the operation of an analog
camera. The film magazine is replaced by a ruggadized mass
storage unit, which can be, in case of the DMC, exchanged
in the air during the flight to extend the capacity, like
swapping film rolls. A new generation of flight management
systems like the Z/1 ASMS Airborne Sensor Management
System controls the camera system and provides information
for the pilot on a display in the cockpit. The disk capacity of
the airborne mass storage is usually enough for a full day
mission. A big advantage is that the camera operator can
have access to the acquired image data between the flight
lines or during the flight back for the mission to the air field.
This is a huge benefit against film cameras because it allows
a real time image quality assessment. But this is only true for
frame sensor based cameras not for push broom or CCD line
sensors based cameras.
The camera operator can have access to the acquired image
data through the onboard computer equipment. A image data
post processing for one image can be done in a few minutes
even with limited computer performance, this is one of the
biggest advantages of frame based cameras against line
sensor cameras. For a first image quality check GPS and
IMU data are not required.
Frame sensor cameras are not depending on this technology,
it can be used optional. Although today modern professional
aerial photo flight will not be executed without the use of
precise GPS information.
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Figure 2 AOPV airborne on-board project viewer
To maintain the quality for a photo flight, information about
cloud coverage is very important. Therefore the ASMS (
Airborne Sensor Management System ) has an integrated
video camera. The video camera displays the image scene
during the time the exposure is taken. A video thumbnail
pertains to each exposure, the thumbnails can be mosaicked
to an overview to get an impression of the complete mission.
The camera operator can then easily identify each exposure
where the cloud coverage was to much and mark these
images for second shot.
12 micron 5
This new functionality is a huge benefit and cost saver for the
photo flight project. The crew can decide in "real time"
without leaving the mission area, if there is a need to repeat a
flight strip or to re-fly single images.
A huge benefit of modern aerial sensor management systems
is a high level of integration to reduce the number of external
devices for the aircraft. For example the ASMS hardware
includes the camera control interface, the control interface
for a gyro stabilized camera mount, a video frame grabber
board, a L1/L2 24 channel GPS receiver and an interface to
the POS 510 control electronic ( IMU for direct geo
referencing )
Figure 3 ASMS Aerial Sensor Management System
4. DMC DIGITAL MAPPING CAMERA
The Digital Mapping Camera DMC is a new frame based
large format aerial camera, designed for high precision large
scale engineering application as well as for small scale
mapping projects.
The DMC uses a CCD frame sensor with a 12 micron pixel
size, which means 144 square micron of light sensitive area.
CCD pixel element
6.5 micron 4
Figure 4 light sensitive area of a CCD pixel element
It is the nature of a CCD that the light sensitivity increases
straight linear with the light sensitive area, which means that
a 12 micron CCD is approx 3.5 times more sensitive
comparing to a 6.5 micron CCD.
