Table 3. Distribution of the differences between a laser grid and echo sounding points in different intervals. 
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Difference 
First campaign 
Second campaign 
Third campaign 
±0.1 m 
12.4 % 
34.9 % 
58.0 % 
±0.3 m 
62.6 % 
86.1 % 
93.2% 
±0.5 m 
92.5 % 
96.8 % 
97.6 % 
±1.0 m 
99.3 % 
99.5 % 
99.5 % 
A negative sign of vertical differences as for the first campaign in Figure 6 indicates that most parts of the laser grid lie 
under echo sounding points. On the other hand, a positive sign like the second campaign shows the laser grid lying above 
echo sounding points. 
As depicted in Table 3, the seabed points of the third campaign are most similar to the echo sounding data. More than 
half of the differences are smaller than ±0.1 m. Additionally, the best results are also observed in the other three 
intervals. In contrast, the point cloud of the first campaign has the largest vertical deviation to the echo sounding data. 
Only 12.4% of the differences lie in the ±0.1 m interval and 62.6% in the ±0.3 m interval. However, most of the 
differences (over 92.5%) of each campaign are smaller than 0.5 m. 
Concerning the quality of the data, laser bathymetry must at least meet the constraints of the IHO Standards for 
Hydrographic Surveys (S-44), Order lb specifications to partly substitute ship-based bathymetry. These standards 
require one laser point every 5o nr (and even full sea floor coverage for Order la). The maximum allowable total 
horizontal uncertainty (THU) and total vertical uncertainty (TVU) at a 95% confidence level are defined by 
THU max = 5 m + 5 % depth, (1) 
TVU max = ±7(0.5 m) 2 + (0.013 * depth) 2 . (2) 
The thresholds are the same for Orders la or lb. In addition, to satisfy the requirements of Order la it must be possible to 
detect cubic obstacles of a size of larger than 2 m in depths up to 40 m. In this study the focus is only on TVU because it 
is more critical for ship navigation, and the horizontal accuracy is difficult to compute from our data due to missing 
prominent objects under water. The vertical quality analysis based on Order lb of IHO (S-44) is listed in Table 4. The 
cells highlighted in yellow represent depths upon one times the Secchi depth, light orange cells indicate depths between 
lx and 1.5x Secchi. 
Table 4. Vertical quality analysis in 1 m depth intervals. 95% must be reached to fulfill IHO Order la/b 
Depth [m] 
TVU max [m] 
Number of points within TVU nlax 
1. Campaign 
2. Campaign 
3. Campaign 
0-1 
±0.50 
88.5% 
93.1% 
91.8% 
1-2 
±0.50 
92.2% 
92.7% 
94.6% 
2-3 
±0.50 
92.6% 
90.4% 
94.4% 
3-4 
±0.50 
93.8% 
92.9% 
4-5 
±0.50 
94.8% 
5-6 
±0.51 
94.2% 
6-7 
±0.51 
91.7% 
7-8 
±0.51 
87.6% 
8-9 
±0.51 
82.7% 
92.2% 
9-10 
±0.52 
70.9% 
50.5% 
10-11 
±0.52 
64.3% 
0.0% 
11-12 
±0.52 
0.0% 
83.9% 
- 
Proc. of SPIE Voi. 9638 96380Z-7