International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
signal ampliutde
-10 -5 0 5 10 15 20
time (ns)
Figure 6. High-resolution sampled transmitter pulse of RIEGL
LMS-Q560. Temporal resolution 50 ps, calculated from
samples on 2000 consecutive transmitter pulses.
Figure 7 shows an example of the echo signal obtained on a
coniferous tree at a distance of about 260 m. Three separate
targets can be identified which can be attributed to different
twigs.
140
120 F
100 F
80 F
60 F
signal ampliutde
40 -
20 F
0 ae. pling. r1 A n A A.
1760 1765 1770 1775 1780 1785 1790 1795 1800 1805
time (ns)
Figure 7. Example of received echo signal of the RIEGL LMS-
Q560 on a coniferous tree in about 260 m distance showing
three distinct targets with distance differences of about 1.5 m.
Digitisation and recording of part of or even the full return
signal by commercial full-waveform airborne laser scanners
like the one sketched above will provide additional information
about the structure of the illuminated surface. This offers the
option of classifying the acquired data based on the shape of the
echo (e.g. separating narrow return echoes from horizontal
terrain surfaces from wide echoes with more than one peak in
wooded areas) Another important advantage is that the
detection of the stop (trigger) pulses can be applied after data
capturing, thus allowing to use different detection methods or
even a combination of methods in order to extract the most
interesting information for a specific application. An end user
who wants to model the vegetation structure has different
requirements on the detection method than a user who is
interested in terrain modelling.
Unfortunately, current systems do not provide any information
about the echo detection method and offer no quality feedback,
even though this information could be very useful for further
modelling steps. In contrast, future systems with full-waveform
206
recording capability will allow to apply one of several pulse
detection methods after data acquisition. By local analysis of
the backscattered signal, it should also be possible to determine
quality parameters for a given range measurement, which can
be used as a direct input into further processing steps.
It appears that full-wave systems will much enhance our
capability to map natural and artificial objects, but this comes at
a cost: Instead of having one or a few trigger pulses the whole
discrete signal must be stored. Major research and development
efforts will be needed in order to develop algorithms and
software that can efficiently transform the recorded waveform
clouds into geo-spatial data sets.
ACKNOWLEDGEMENTS
The contribution of Christian Briese was supported by the
Austrian Science Foundation (FWF) under grant no. P-15789.
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