The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Voi. XXXVII. Part B5. Beijing 2008
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Focal plane
ABC
Figure 5. Construction of focal plane and principle of stereo
imaging
3.3 Design of laser ranger
Laser module gave three footprints every other four
hyperspectral image lines, shown in figure 6. The laser
footprints were registered strictly with the hyperspectral image
pixels, which was fulfilled by opto-mechanical design as a
whole consideration and calibration in the lab.
g
P
n
g
s
B
8
a
a
a
a
P
direction
ti
Figure 6. Registration of laser footprints and hyperspectral
pixels
Laser module didn’t employ any scan components, but adopted
two beam splitters to obtain three desired points from a laser
beam, shown in figure 7. The original laser beam was divided
into three equivalent portions by energy. The right and left beam
were directed at ±11° with respect to central vertical beam.
The energy of laser emitter in our system is less than lOOmJ, the
divergence angle is better than 3 mrad, the repetition frequency
is 20Flz, and the central spectrum 1064 pm. The optical aperture
of receiving optics is 60 mm, and IFOV 4mrad, shown in figure
8. The left part emits laser beam, and the right part receives
reflection beam, then is converted into electronic signal through
APD (Avalanche Photodiode). A precise time interval
measuring board was deployed to arbitrate and calculate the
time interval between emitted pulse and received pulse, which
ensured the distance resolution of 7.5cm.
3.4 Stabilized platform and attitude & position
measurement subsystem
It is pretty common to deploy stabilized platform and attitude &
position device in photogrammetric and remote sensing system
nowadays. In virtually, this is not the best method, perhaps a
high enough precise three dimensional stabilized platform is
better in theory, however the former is still more reasonable and
flexible on account of current situation of research,
development and cost.
In our system, the stabilized platform, PAV30 of Leica
Corporation, was employed to stabilize imaging sensors.
Though the accuracy of PAV30, ±5°, is not very high, it is
enough for general airborne application and basically ensures
that there are no big gaps during and between flight strips,
which is very important for a successful application.
Moreover, we installed a start-of-the-art GPS/INS system, POS
AV/510, developed by Applanix Corporation. POS AV/510
device can provide real-time and post-processing delivery of
attitude and position with excellent accuracy and precision. It
operates using combined IMU (Inertial Measurement Unit) and
GPS (Global Positioning System) receiver. The position
information from the GPS system and the 3-axis attitude and
position data from IMU are combined in a tightly Kalman filter
to provide x, y and z position values as well as roll, pitch and
true heading. The stated accuracy is 5-30 cm in position, 18" in
roll and pitch, 28.8" in true heading when operated with
differential GPS and made a post-process.
Splitter 1 Splitter 2
Reflection minor
Figure 7. Drawing of laser beam splitting
Laser emitter
Beam splitters
.APD an as'
All sensors, including one of POS AV/510, are bolted directly to
platform frame, and must be prohibited from any relative
motions among them.
3.5 Data acquisition and storage subsystem
In this system, we employed a master control computer to
operate all sensors, as shown in figure 9. The connection
interface between the master computer and sensors is local
network. The operator interface controls work mode and status
of all sensors, and also receives some image data to monitor
through net cables. After commencing to acquiring data, all
sensor modules sent an event pulse, which marked the exposure
moment of every scan line, into POS AV/510.
Figure 8. Optical construction of emitting and receiving
Figure 9. Working flow of data acquisition and storage
The hyperspectral and laser data are can be stored in a 200GB
