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Figure 3. Number of seabed points in several normalized seabed depth intervals.
In addition to the quantitative analysis, we investigate the point distribution with respect to the normalized seabed depth.
The result is presented in Figure 3, which shows the percentage of seabed points in several depth intervals. For the first
campaign the observed seabed points mainly lie in the range of up to 0.7/ Secchi depth, the curve then falls strictly
monotonously. For the second and third campaign most of the points lie in the range of up to 1.3 x Secchi depth. In
contrast to the first campaign maximum values appear at 0.5-1.0x Secchi depth. Of course, it has to be kept in mind that
the covered area per depth interval differs from campaign to campaign (see Figure 2, and also Section 4.3).
4.2 Point density
In this section we examine the density of the seabed points based on the normalized seabed depth. The results are given
in Figure 4 presenting the number of seabed points per m 2 at an interval of 0.1 x Secchi depth. For the calculations the
amount of points within one 5x5 m 2 grid cell is divided by 25 for normalization reasons. In contrast to Figure 3 the
influence of the varying area size of a particular depth level is eliminated in this case. As mentioned above the shallow
region between 0 and 0.2-0.5x Secchi depth is not complete. In the first campaign the point density decreases with
increasing depth. Up to 0.5 x Secchi depth the results of the first campaign provide a better point density than the other
campaigns, probably due to the higher measurement rate. The shapes of the point density distribution curves for the other
two campaigns are similar to each other. Their maxima are at approximately 2.4 points/m 2 and they decrease relatively
slowly.
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o
a.
Secchi depth
Figure 4. Point density of the seabed points with respect to the normalized seabed depth.
Proc. of SPIE Voi. 9638 96380Z-5
