In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
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technology with a 1-ns sampling rate would provide much more 
detailed information about the complex vertical structure of 
vegetation. It is for this reason that, in the last decade, full 
waveform technology has been the only choice for lidar 
applications requiring analysis of complex vertical targets with 
fine structure. However, the introduction of the ALTM Orion, 
representing a new breakthrough in discrete return lidar 
technology, has changed this situation. 
3. ALTM ORION: NEW-GENERATION AIRBORNE 
LIDAR 
The ALTM Orion system represents a radical departure from 
previous generations of airborne lidar instruments. First, the 
physical form factor—size, weight and displacement—has been 
reduced by a whole order, making the Orion the first ultra 
compact complete lidar solution, with the volume reduced by 
factor of 7 compared to the previous ALTM 3100 and Gemini 
models (Hussein et al., 2009). Second, the lidar data produced 
by the Orion has established a new benchmark in the industry 
for data quality, accuracy and precision (Ussyshkin and 
Theriault, 2010). It was shown that the outstanding 
performance characteristics of both ALTM Orion models, 
Orion-M and Orion-C, include a highly efficient system design 
that provides the best combination of maximum area coverage 
rate, exceptional ground data accuracy and precision, and the 
sub-centimeter precision of data comprising small-size complex 
targets such as the thinnest wires in power line corridors. 
The third radical advantage provided by both ALTM Orion 
models is the revolutionary small minimal pulse discrimination 
distance, which is of particular importance in complex target 
mapping applications such as urban and low-canopy vegetation 
mapping. Figure 3 shows an example of ALTM Orion-M data 
collected over 6-m high vegetation, with four returns for one 
emitted laser shot with a minimum pulse separation of 73 cm. 
Such a small sub-meter pulse separation has never been 
achieved before by any discrete return airborne lidar, and in 
combination with the excellent ability of the system to detect 
weak partial signal returns from low-canopy layers of 
vegetation, it provides unprecedented data quality with 
exceptionally rich content. 
Figure 3. ALTM Orion-M: An example of a four-return 
record for one emitted laser pulse with a minimum pulse 
separation distance of 0.73 m. 
Figure 4 shows another advantage of the exceptionally small 
pulse separation distance of the ALTM Orion. The data 
presented in this example was collected over a dense cornfield 
2.2 m in height, and yet the lidar system was still capable of 
detecting three consecutive pulse returns, with the last showing 
strong intensity representing the ground return. The unique 
capability of the ALTM Orion to generate data so rich in 
content with fine sub-meter elevation resolution from dense 
cornfields enables the user to take data analysis to a different 
level with highly accurate biomass calculations. This was not 
previously possible with discrete return lidar data without using 
full waveform technology. 
Figure 4. ALTM Orion-M: Three consecutive pulse returns 
with a minimal sub-meter pulse separation are detected over 
dense cornfield, while the last return represents the signal 
penetrated from the ground. 
Figure 5 illustrates the even more impressive pulse separation 
capabilities of the ALTM Orion-C with a minimal pulse 
separation distance of 68 cm. As one can see, these sub-meter 
vertical target discrimination characteristics would provide the 
quality of mapping of complex vegetation structures similar to 
that usually expected only for full waveform digitizer data. 
Thus, looking at the evolution of the discrete return airborne 
lidar technology presented in Figure 5, one can see a clear trend 
towards the sub-meter scale of vertical discrimination distance, 
which bridges the capabilities of advanced discrete return lidar 
and full waveform technology to map complex 3D targets. 
Moreover, it will be shown in the next section that, by 
combining range and intensity data information from an 
advanced multiple return lidar, a simplified waveform analysis 
can potentially be applied to discrete return data in a way that is 
similar to that done for full waveform data. 
ALTM 3100 
AR1.2 
AR1.2 
AR2.3 
AR3.4 
Figure 5. Evolution of minimal pulse separation for discrete 
return airborne lidar systems. 
4. DISCRETE RETURN ANALYSIS 
4 Range ■ 2.14m 
ALTM Gemini 
ARange = 1.45m 
ALTM Orion-M 
ARange = 0.73m» 
ALTM Orion-C 
ARange » 0.68m 
1 st Return H 2nd Return ■ 3rd Return Ml 4th Return §§ 
The simplified analysis of discrete multiple returns presented in 
this section is based on the approach used for full waveform 
data analysis described by Chauve and co-authors (Chauve et