International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
2. DEVELOPMENT OF THREE DIMENSIONAL
CANOPY STRUCTURE MEASUREMENT SYSTEM
2.1 Canopy Crane as Measurement Platform
The canopy crane as our research platform was established on
March 2000 as a JST CREST Project entitled 'Mechanisms of
Atmosphere-Ecosphere Interaction in Tropical Forest Canopy'
(Nakashizuka et al, 2001) in cooperation with Forest
Department, Srawak. Figure 2 is the canopy crane.
Figure 2. Canopy Crane as Our Platform
This crane is about 80m tall height with 75m arm length. It is
equipped with observation stages at 4 levels (24, 43, 58 and
75m above the ground) and elevator to reach the control cabin.
Using the gondola of this canopy crane, it can make us possible
to access the canopy three-dimensionally.
The crane stands at the center of 4ha plot where all individual
trees (DBH: Diameter Blest Height > 10cm) have been mapped
on DEM which generated by ground survey, measured and
identified. This facility can solve the difficulty to reach the
forest canopy and prevent our studies.
2.2 Laser Profiler Based Measurement System and its
Configuration
Our developed laser profiler based measurement system mainly
consists of system operation PC, laser profiler, its mount system,
digital camera, and power supply equipments. PC is equipped
the specified software in order to control all of instruments
operations, measurement and data recording. The laser Profiler
mount system is used for fixing the laser profiler on the crane
gondola and operating laser beam in the perpendicular axis with
0.25 degree. Power supply equipments enable use to provide
stable and continuous electricity at any time.
3. MEASUREMENT AND DATA PROCESSING FOR
VIRTUAL FOREST RE-CONSTRUCTION
As the results of brief investigation of 4ha plot canopy structure,
the maximum, minimum and average distances from the crane
arm to the top of canopy surface had already obtained and they
are 58m, 27m and 45m respectively. Also this measurement
system confirmed to have a good enough performance under the
condition of less than 50m distance from scanner to the target
through our laser profiler capability examination.
3.1 Measurement Concept
Figure 3 is illustrated how the laser beam irradiates to the
canopy surface and measures the distance to the target canopy,
Here measurement system is introduced to one measurement
point by the crane arm swing and both forward-backward and
upper-lower moving of gondola (refer yellow lines). Blue
rectangle area in this figure corresponds to the area where the
developed system can observe at one time. In this case, the laser
beam is irradiating from -30 to +30 degree with 0.25 degree
resolution in both X, Y axes.
Figure 3. Concept of 3D Measurement using Canopy Crane
3.2 Measurement Geometry and Axes Adjustments
Figure 4 is illustrated the measurement geometry and its
overlook. (Point-i,i=1, 4) is a measurement point. The blue
dotted line is the global coordinate system and its coordinate
expressed by F(X, Y, Z). The black solid line at (point-i,i=1,4)
is an obtained scanner coordinate system (F(X;,Y;,Z;),i=1,4). In
order to integrate all independent measured coordinate systems,
the difference between global coordinate system F(X,Y,Z) and
each different coordinate systems (F(X;,Y;,Z;),i=1,4) has to be
adjusted as the pre-processing of scenes mosaic.
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Figure 4. Measurement Geometry
Here all errors have to be corrected by using the differences
between F(X, Y, Z) and F(X;, Yi, Zi) in X, Y, Z axes. And they
can be classified into two kinds of errors. One of errors is à
rotating error. It is defined by an angle (Ad) in Z axis. The
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