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 
Pulse is a signal model as a function of time. There are lots of 
pulse model designed according to shape, width and power. In 
this study, we adopted the modified pulse model (see Figure 10), 
as represented in Eq. (4). In Eq. (4), FWHM is Full Width at 
Half Maximum of the pulse (Carlsson ef a/, 2001). 
Figure 11 shows the generated return pulses by delaying the 
pulse model, which is resized in order that the integral of pulse 
is the received energy of sub-beam calculated in radiometric 
simulation, by the range computed in geometric simulation. 
Waveform, then, can be made by summing these return pulses, 
as you can see in Figure 12. 
_ FWHM 
, 
1\==e",T 
p T 3.5 (4) 
  
  
Figure 10. Modified Gaussian pulse model 
  
po 
Br 
  
eo 
Oh 
  
  
oo 
ant 
  
eo 
NM 
NI ME CM LE 
/ 
g Lada 
  
  
Energy [md] 
ex 
Ch 
LLLI S CELL] 
I L I I 1 I 4 s L 
4 5 8 10 12 14 16 18 20 
Time [ns] 
ro H 
Figure 11. Generated return pulses of 5 sub-beams 
  
Energy [md] 
  
  
  
  
Time [ns] 
Figure 12. Waveform generated by summation without noise 
Since a detector receives not only the transmitted laser pulse but 
also noise, waveform may include signal noise. Main noise 
sources are background sunlight, dark current, thermal and shot 
noise. Due to the many parameters that contribute to noise 
signal, it is difficult to perform the noise modelling precisely. 
Consequently, we generated the noise signal by random 
numbers that follows Gaussian distribution with the standard 
deviation of NEP (Noise Equivalent Power) (Blanquer, 2007). 
Figure 13 shows the generated noise signal by considering SNR 
determined properly. Lastly, waveform with noise, as shown in 
Figure 14, can be generated by combining the signals in Figure 
12 and Figure 13. 
9.15 
0.1 
e 
eo 
a 
Energy [mJ] 
> 
5 o 
à 
  
n 2 4 5 8 
10 12 14 16 18 20 
Time [ns] 
Figure 13. Pseudo signal noise generated by NEP 
0.3 
   
  
Energy [mJ] 
e 
hà 
  
  
  
Figure 14. Simulated waveform with noise signal 
For the pulse detection, we employed CFD (Constant Fraction 
Discrimination). It is able to detect the noisy pulse with good 
accuracy efficiently. The zero crossing points of the S-shaped 
profile in Figure 15 are the return times of backscattered echoes 
detected by CFD. Figure 16 show the simulated waveform and 
the detected times, which indicate near the peaks of the return 
pulses. 
ca Zero-crossing point 
    
Energy {m} 
  
$ RR 14 16 18 26 
Time {na} 
Figure 15. S-shaped profile by CFD 
Energy [mJ] 
  
  
  
02 BU 
Time [ns] 
Figure 16. Waveform signal and detected return times 
(blue star: return times detected by CFD)