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. 
966 
dZ [m] 
0.090 FI 
0.056™ 
0.022 
-0.011 
-0.045 
-0.079 
-0.113 
-0.146 
-0.180 
(a) M[ 
dZ [m] 
0.0901 I 
0.056n 
0.022 
-0.011 
-0.045 
-0.079 
-O.loM 
-0.1461 
-0.18o| 
(b) M 2 
25m 
dZ [m] 
0.0901 I 
0.056™ 
0.022 
-0.011 
-0.045 
-0.079 
-0.113 
-0.146 
-0.180 
(C) M 3 
Figure 7. Deviation dZ between refraction corrected ALS point 
clouds (colored) and TLS point cloud (grey ) at the pool bottom. 
3 
(a) Mi 
3 
(b) M 2 
3 
(c) M3 
dXY [m] 
0.156 fl 
0.087 
0.0181 
dXY [m] 
0.156 fl 
0.087 
0.0181 
dXY [m] 
0.156B 
0.087 
0.0181 
Figure 9. Deviation dXY between refraction corrected ALS 
point clouds (colored) and TLS point cloud (grey) at the 
concrete base in meter. 
Figure 8. Water surface point density in points per square meter. 
Figure 7 shows the comparison between the corrected ALS point 
clouds and the TLS reference point cloud at the pool bottom for 
one flight strip at a height of 500 m. Bottom points near the pool 
wall are eliminated from the evaluation to ensure that only areas 
with natural wave movements conforming to the oceanographic 
wave model are included in the analysis. Furthermore, shallow 
water areas are excluded, where the water depth is not sufficient 
for a meaningful investigation. The deviations demonstrate that 
the depth errors decrease with increasing complexity of the water 
surface representation. The main improvement results from the 
consideration of the local height of the water surface elements. 
The local surface tilt is less relevant for the depth coordinates. 
The differences between the ALS point cloud corrected with the 
simplest correction method Mi and the TLS reference point cloud 
clearly displays effects of the local wave pattern on the water 
body bottom (Fig. 7 (a)). The other two correction methods leave 
some remaining errors as well, but less distinctive. The compar 
ison with the density and distribution of the water surface points 
visualized in figure 8 shows that the largest deviations to the ref 
erence data occur in areas with less water surface information. 
The investigation of the lateral deviations between corrected ALS 
point clouds and TLS reference point cloud is limited by the small 
number of usable ALS points solely available for the 500 m flight 
strips. Figure 9 presents the results for the different refraction 
correction methods. The deviations vary between 1.8 cm and 
15.6 cm. Overall, the lateral errors decrease with increasing water 
surface complexity. 
Table 3 summarizes the results for all flight strips. The root mean 
square error (RMSE) of the lateral coordinate displacement varies 
in the range of 8.24% to 11.01 %. The depth displacements are 
comparatively small (RMSE 1.08 % to 2.20 %), whereas the dis 
placements decrease with increasing water surface complexity. 
Effects due to the different flying heights are not recognizable. 
dXY RMSE 
dZ RMSE 
500 m 
600 m 
700 m 
500 m 
600 m 
700 m 
Ml 
11.01 
- 
- 
3.54 
3.65 
3.68 
M 2 
8.30 
- 
- 
2.02 
2.33 
1.83 
M3 
8.24 
- 
- 
1.80 
2.20 
1.73 
Table 3. RMSE of the discrepancies between refraction 
corrected ALS data and terrestrial reference data in percent of 
the water depth.