The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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3.1 Parameter Setting 
To generate the simulated LADAR data, we need to set up the 
parameters such as the sensor parameters, the flight path of the 
platform, and the systematic errors associated with the sensors. 
The system parameters used for the simulation are presented in 
Table 2. The pulse rate is the number of laser pulses transmitted 
per second, and the scan rate is the number of scans per second. 
The number of laser pulse per one scan is then derived from the 
scan rate and the pulse rate, which is 600 times. The scan angle 
indicates the scan range. In this case, the 20 degree of scan 
angle means that the system scans -10 ~ 10° range with 
respect to the vertical line at the center. 
Parameter Name 
Unit 
Value 
Pulse Rate 
kHz 
30 
Scan Rate 
Hz 
50 
Scan Angle 
deg 
20 
Table 2. The systematic parameter of the LADAR system 
The Flight Path of the Platform: The flight path in the 
simulation is assumed as a strip starting from (-150, 550, 1500) 
to (150, -550, 1500) with the flight speed of 30 m/s. 
The systematic errors associated with the sensors assumed in 
this simulation are described in Table 3. These parameter values 
are carefully determined by considering the error range of a 
typical airborne LADAR system. The other parameters not 
specified in Table 3 among the error parameters incorporated 
into Eq. (2) are negligible comparing to the specified ones and 
thus assumed to be zero. 
Bias 
Symbol 
Unit 
Value 
GPS bias, X 
^WG w 
m 
2 
GPS bias, y 
m 
1 
GPS bias, z 
m 
0 
INS bias, omega 
deg 
0.1 
INS bias, phi 
deg 
0.2 
INS bias, kappa 
deg 
0 
Range bias 
A r 
m 
0.0 
Table 3. The systematic errors associated with a LADAR 
system 
3.2 Input DEM 
The input DEM (Digital Elevation Model) used for the 
simulation is shown in Figure3. This DEM has a variety of 
terrain slopes. Its grid spacing is 10m. It covers an area of 1.2 
km by 2.0 km. This area is enough to include the flight path 
above. 
Figure 3. The input DEM used for simulation 
3.3 Simulation Results 
The simulation methods have been programmed with the C++ 
language and run on a standard Pentium desktop computer. The 
simulator generates about 1,140,600 points for the running time 
of 38.02 seconds. The ground coverage area of the simulated 
LADAR data is shown in Figure 4. The central bold solid line 
of the ground coverage indicates the flight path. The point 
density of the simulated LADAR data is 0.664 points/m 2 ; its 
point spacing is 1.774 m; the range of its x-coordinate value is - 
344.759 ~ 361.978 m; the range of its y-coordinate value is - 
609.839 ~ 604.533 m. 
1000 
800 
600 
400 
200 
0 
200 
•400 
-600 
800 
-1000 
-500 0 500 
* [mj 
Figure 4. The flight path and the coverage of simulated data 
Figure 5 shows the simulated LADAR points on the input 
DEM; and Figure 6 shows only the simulated LADAR points. 
As one of the verification processes, the elevation differences 
between the simulated LADAR points and the input DEM are 
computed. Their distributions are shown in Figure 7. The above 
histogram shows the error distribution of the simulated data 
without any systematic error. As expected, the elevation 
differences are relatively small since it does not consider any 
error. These small errors are mainly caused from not the 
systematic errors but the interpolation of the input DEM. 
However, as shown in the below one, the simulated data with 
systematic errors naturally include more errors.