International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
4. CONCLUSION 
This paper presents a wavelet-based detector to detect the 
responded echoes in LIDAR waveforms. Some simulated 
waveforms with noises are made to test the limitation of the 
detector. The detector treats an echo as an effective return only 
if its SNR exceeds a threshold. The experiments suggest that a 
weak echo can be detected as long as its SNR is greater than 16 
dB. Normally an echo has SNR lower than 22 dB will be missed 
in the online process of an ALS. The experimental results also 
show that the detector can resolve two distinct scatters as long 
as the echoes are separated with a distance larger than the range 
resolution of the ALS. In addition to the analysis on simulated 
data, the detector has also been applied to a set of waveform 
data captured with Leica ALS60 for a forested mountainous 
area. In addition to the total number of echoes provided by the 
instrument, the detector increasingly found 18% more of the 
original number of echoes. This result shows the ability of the 
proposed detector in finding weak and overlapped returns from 
waveforms. These extra echoes can potentially be used to 
improve the estimation of canopy height and ground surface for 
a forested area. 
REFERENCES 
Chauve, A., C. Vega, S. Durrieu, F. Bretar, T. Allouis, M. 
Pierrot Deseilligny and W. Puech, 2009. Advanced full- 
waveform lidar data echo detection: Assessing quality of 
derived terrain and tree height models in an alpine coniferous 
forest. International Journal of Remote Sensing 30(19), pp. 
5211-5228. 
Jiao, Long, Suya Gao, Fang Zhang and Hua Li, 2008. 
Quantification of components in overlapping peaks from 
capillary electrophoresis by using continues wavelet transform 
method. Talanta 75(4), pp. 1061-1067. 
Mallet, Clement and Frederic Bretar, 2009. Full-waveform 
topographic  lidar: State-of-the-art. ISPRS Journal of 
Photogrammetry and Remote Sensing 64(1), pp. 1-16. 
Mallet, Clement, Florent Lafarge, Michel Roux, Uwe Soergel, 
Frederic Bretar and Christian Heipke, 2010. A Marked Point 
Process for Modeling Lidar Waveforms. IEEE Transactions on 
Image Processing 19(12), pp. 3204-3221. 
Pirotti, F, 2011. Analysis of full-waveform LiDAR data for 
forestry applications: a review of investigations and methods. 
iForest - Biogeosciences and Forestry 4(1), pp. 100-106. 
Shao, Xueguang, Wensheng Cai and Peiyan Sun, 1998. 
Determination of the component number in overlapping 
multicomponent chromatogram using wavelet transform. 
Chemometrics and Intelligent Laboratory Systems 43(1-2), pp. 
147-155. 
Wagner, W., A. Ullrich, V. Ducic, T. Melzer and N. Studnicka, 
2006. Gaussian decomposition and calibration of a novel small- 
footprint full-waveform digitising airborne laser scanner. ISPRS 
Journal of Photogrammetry and Remote Sensing 60(2), pp. 100- 
112. 
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