In: Wagner W., Sz6kely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
610 
5 
more detailed analysis, but the preliminary results partly 
presented here demonstrate the huge potential of discrete return 
technology, the evolution of which has achieved a level 
approaching in some aspects that of full waveform technology. 
The discrete return data analysis described above has much 
similarity with the procedures applied to full waveform data 
analysis, and might potentially be used in applications similar 
to those which to date have been considered as solely belonging 
to full waveform technology. 
The modeling of the discrete signal profiles for vegetation data 
presented above could be compared with the analysis of the full 
waveform data collected over similar vegetation targets 
(Wagner et al., 2004). An example of a coniferous tree profile 
with a total length of 35 ns recorded with a 1-ns sampling rate 
showed three Gaussian-shaped peaks with a target separation 
distance of 1.5 m. Comparing these numbers with the ALTM 
Orion data presented in Figure 3, one can conclude that the 
discrete return lidar data of enhanced quality can provide 
equivalent or in some aspects better representation of 
vegetation structure than the full waveform data. Another 
example (Wagner et al., 2004) of the full waveform data 
collected over a wheat field of 2.5 m height can be compared 
with the cornfield data collected by ALTM Orion (Figures 4 
and 7), where three discrete return data with excellent target 
separation characteristics provide equivalent or even better 
input for Gaussian modeling of the crop and ground signals. 
This may be considered an indication of a potential fusion of 
two types of airborne lidar data on the application side when 
similar approaches and tools can be used for the analysis of 
both data types. However, it is clear that the full waveform 
technology will continue to be essential and irreplaceable for 
applications requiring the analysis of very complex vertical 
targets including consideration of pulse-broadening effects 
associated with laser beam-target interaction and interception 
geometry (Schaer et al., 2007). In these cases, modeling and 
deriving physical parameters should be more reliable if based 
on full waveform technology. 
5. CONCLUSION 
The analysis presented above indicates that the evolution of 
discrete return airborne lidar technology has achieved a new 
level, with capabilities that can be considered equivalent to 
those of full waveform technology for many applications. The 
trade-off between the high complexity and cost associated with 
the handling of WFD data on the one hand, and the 
conventional discrete return data of enhanced quality on the 
other hand, has the potential to create a new application niche 
in the lidar industry. In this niche, top-quality dense point 
clouds, with fully recorded intensity information for each of 
multiple returns, may provide sufficient information for 
modeling the received waveforms. 
The fine pulse separation characteristics and vegetation 
penetration capabilities demonstrated by the ALTM Orion, the 
new advanced discrete return airborne lidar, is based on 
Optech's long experience with full waveform digitization and 
its recent leading-edge algorithm development. This real-time 
waveform analyzer enables users to consider new applications 
for discrete return data of sub-meter vertical resolution and sub 
centimeter precision. It has been demonstrated that discrete 
multiple return data with enhanced characteristics can provide 
information sufficiently rich in content for a waveform type of 
data analysis, applying similar methodology but without the 
high complexity and cost associated with the handling of full 
waveform data. 
Acknowledgements 
The authors are very thankful to Brent Smith, Eric Yang, Mike 
Sitar and Helen Guy-Bray for fruitful discussions. 
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