The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008 
and to understand how the pulse interacts with the surface, a 
theoretical knowledge of the influence of the geometric and 
radiometric properties of the illuminated surface (i.e., the 
differential laser cross-section) on the shape of the waveforms is 
required. Quantifying specifically both geometric and 
radiometric influence of a object on the received waveform is 
undoubtedly the most promising line of research for that purpose. 
5. FUTURE RESEARCH DIRECTIONS 
Researches on full waveform data are still at their beginnings, 
but seem very promising in terms of automatic data extraction. 
However, if the technology seems well managed by 
manufacturers, many questions will arise for future work. 
Whatever the scenario type will be, if it is clear that full 
waveform LiDAR data provide range information, it is still 
expected to be fully proved that they contain physical 
assessments of the backscattering properties of the illuminated 
surface. Among other interesting points, two of them seem 
essential and have to be investigated in priority: 
• The influence of the surface geometry and radiometry 
onto the shape of the waveform. 
• The influence of the lasers wavelength onto the 
measurement itself. 
Answering these points needs a modelling step that could be 
based on a ray-tracing model or even more complex, a 
electromagnetic model, which bases on the wave characteristic 
of the light, e.g. to investigate speckle effects. Such approaches 
will consider the LiDAR footprint size, the beam divergence, the 
sensor FOV, the wavelength, the direction of the laser beam 
propagation etc., but also the characteristics of the scenario (tree 
species, building geometry...). It also necessitates an 
experimental step to build a data base of optical responses in 
various optical wavelength over various features. 
Furthermore, most of topographic LiDAR systems work with 
a single wavelength. The recording of several waveforms, each 
of them emitted at a different wavelength could enhance the 
object description. These so called hyperspectral laser systems 
could deliver for instance multiple intensity information of 
surfaces instead of only monochromatic information. Finally, 
scientists of the ISPRS community would take high benefit of 
having a better knowledge of commercial LiDAR systems, 
particularly of its system specifications, which is usually 
different for each sensor and most of the relevant information is 
kept secret by the manufacturers. 
The extensive use of full waveform LiDAR data leads to think 
of a new data format and data management system as LAS 
format and TerraScan© for point clouds. The format could be 
based on a multiple layer structure in the sensor geometry, each 
of them linked to the others by pointer arrays (Figure 3). Among 
important layers, there are a raw data layer containing all 
waveforms, a georeferencing layer containing the trajectory 
and sensor information interpolated at each measurement and a 
modelling layer containing the parameters of the analytic 
description of the waveform. A XML meta file could describe 
each layer. An orthorectified geometry should be generated in 
terms of GUI and linked to the sensor geometry. 
6. CONCLUSION 
We have presented in this article the main lines of researches on 
full waveform LiDAR data performed, especially in the ISPRS 
community. Even if these data have been used for only a short 
time now, it seems that fruitful and promising results have come 
out in the recent years. Many problems have to be sorted out 
before using these data as multi-echo LiDAR data are. 
Nevertheless, the tasks are extremely challenging since it is a 
new and wide research area, which begin to deals with physical 
remote sensing. 
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