The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-2, 2018 
ISPRS TC II Mid-term Symposium “Towards Photogrammetry 2020”, 4-7 June 2018, Riva del Garda, Italy 
This contribution has been peer-reviewed. 
https://doi.org/10.5194/isprs-archives-XLII-2-961-2018 | ©Authors 2018. CC BY4.0 License. 
967 
5.3 Comparison 
Overall, the effects predicted in the numerical simulation are con 
firmed by the experimental validation. Compared to the experi 
mental results the simulation tends to be too optimistic. The wave 
induced height and planimetry coordinate errors obtained from 
the experimental validation are 10 times larger than the values 
predicted in the simulation. The main reason is the limitation 
of the simulations to identical forward and backward laser pulse 
paths here. Effects of dispersion and diffuse reflections at the 
water bottom are neglected. 
Another reason is the difference between real and simulated water 
surface. The simulated wave pattern is characterized by smoother 
wave crests as shown in figure 4. Furthermore, the artificial char 
acter of the machine-made waves is not optimally reproduced 
with the oceanographic statistics based surface wave model for 
ocean waves, especially reflections of waves at the pool wall. 
Moreover, the distribution of the water surface points differs in 
simulation and experiment. The simulation is based on a homo 
geneous distribution with 1 respectively 10 points per square me 
ter. In contrast, the water surface representation used for the ex 
perimental validation is characterized by an inhomogeneous dis 
tribution of water surface points. Figure 8 shows an example for 
a typical point distribution present in the data sets. The point den 
sity varies from 0 to 8 points per square meter. The results of the 
experimental validation remain mean values for the whole inves 
tigation area averaging zones with high and low point density. 
Assessing the results of numerical simulation and experimental 
validation, furthermore, the different level of detail used for the 
ray path modeling has to be considered. In contrast to the simu 
lation, the refraction correction of the measurement data does not 
take into account the beam divergence, instead the laser pulse is 
treated as infinitesimal small line. 
6. CONCLUSION 
This contribution investigates the effect of wave patterns on coor 
dinate accuracy in airborne LiDAR bathymetry. For this purpose, 
a numerical simulation as well as an experimental validation was 
carried out for a real world scenario. The comparison of the er 
rors predicted in the simulation and the errors derived from real 
measurement data show a consistent tendency. However, the ex 
perimental validation reveals significantly larger errors than pre 
dicted in simulation. 
Furthermore, the results indicate that the effect of wave patterns 
is not sufficiently considered in common refraction correction 
methods. Therefore, a next step could be to model local wave 
patterns on the basis of real LiDAR bathymetry water surface re 
flections. As a final result, point-wise strict coordinate correction 
terms can then be applied in order to increase the accuracy poten 
tial of airborne LiDAR bathymetry. 
ACKNOWLEDGEMENTS 
The research work presented in this paper has been funded by 
the German Research Foundation (DFG). We would also like to 
thank Milan Geoservices for acquiring the LiDAR bathymetry 
data used in this study. Finally, our thanks goes to the operator of 
the swimming pool, sbf GmbH Radebeul, providing access to the 
swimming pool facility and controlling the wave machine. 
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