In comparison with echo signals between Japanese cedar and
Zelkova serrata, the initial slope of the first peak of Zelkova
serrata was steeper than that of Japanese cedar. Crown shapes
of Japanese cedar and Zelkova serrata are the conical- and the
bowled-shaped, respectively. We considered that the reason of
the difference was the shape of crown. As the results, we
considered that the developed simulator was able to simulate the
difference of shape of crown well.
7.2 The effects of the illumination angle and the slope of
the ground
Figure 3 is the effect of the illumination angle and the slope
of the ground. Figure (a), (b), (c) and (d) stands for scenario
no.l, no.2, no.3 and no.5, respectively. Full width half
maximum (FWHM) of (b) became wider than that of (a), since
optical paths between these were changed. In comparison with
between (a) and (c), the echo signal of (c) differed significantly
from (a). FWHM of the first peak of (c) was wider and the
second peak had two peaks. On the other hand, in case of (d),
the two peaks of the second peak in (c) disappeared in (d).
Folative tens:
Relative snc ty
(d)
Figure 3. The effect of the illumination angle and the slope of
the ground. (a), (b), (c) and (d) stands for scenario no.1, no.2,
no.3 and no.5, respectively.
7.3 Comprehend of the elementary process of the
generation of echo signal using the visualization tool
It is difficult to understand the elementary process between
the laser beams and the object using only the results of the echo
signal. For example, in case of scenario no.3, the second peak
had two. However, in case of scenario no.5, two peaks
disappeared. Then, the reason was considered using the
visualization tool. Figure 4 shows the results of visualization of
intersections derived from scenario no.2 (a) and no.5 (b). Sub
windows stands for view at different directions, respectively.
The upper left window is top view, the upper right window is
left view, the bottom left window is right view and the bottom
right window is perspective view. Dot symbol is intersections
between sub laser beams and objects. As a result of analysis of
intersections on the objects, two peaks corresponded to the
distribution of intersections (bottom left view of (a)). There
were two areas which had high density intersections on the
surface of the ground. On the other hand, in case of figure 4 (b),
high density area was one (bottom left view of (a)). The
visualization tool was able to help to comprehend the
elementary process of the generation of echo signal.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
TE Y
(b)
Figure 4. The results of visualization of intersections derived
from scenario no.2 (a) and no.5 (b)
8. CONCLUSIONS
A waveform simulation model for complex forest
environments using 3D object was presented in this paper.
Since the echo signal depends on the sensor configuration, the
target structure and terrain condition, we implemented these
features in the simulator. According to the simulation using
scenarios, these results indicated that the simulator was able to
generate the echo signal under various conditions. Moreover,
the visualization tool indicated that it was quite useful for
understanding the elementary process of the generation of echo
signal.
However, the simulator is preliminary result and we have not
evaluated the simulator by an actual data yet. Moreover, an
effect of noise has not been validated.
In our future work, we plan to evaluate the simulator by using
an actual data.
References
Clark, M. L., Clark, D. B., and Roberts, D. A., 2004. Small-
footprint LiDAR estimation of sub-canopy elevation and tree
height in a tropical rain forest landscape. Remote sensing of
Environment, 91, 68-89.
Goodwin, N R., Coops, N. C., and Culvenor, D. S., 2007.
Development of a simulation model to predict LiDAR
interception in forested environments. Remote sensing of
Environment, 111, 481-492.
Næasset, E., 2004. Effects of different flying altitudes on
biophysical stand properties estimated form canopy height and
density measured with a small footprint scanning laser. Remote
sensing of Environment, 91, 243-255.
Sun, G., and Ranson, K. J., 2000. Modelling LiDAR returns
from forest canopies. IEEE Transactions on Geoscience and
Remote Sensing, 38, 2617-2626.
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