Environmental and resource applications
If available, additional data about each survey, such as reference gauge
levels, measurement techniques, assigned ship, date, and time, were
included into the relational GIS database. During evaluation and interpretation of the results this metadata turned out to be very important.
A systematic influence of different echo-sounding systems was found
with the help of that metadata (fig. 5).
Evaluations and data quality (examples
In this chapter some examples of the methods used for further evaluations
of the GIS database are described. To enable regional comparisons, evaluations were conducted for more than 5 000 km
2 along the shoreface of
the German Bight. All evaluations are based on the same GIS database.
Changes of depth
On the basis of the grid database changes in depth between two different
surveys can be calculated and represented spatially within the GIS.
With these changes of depth mass balances can be calculated for any
area. The result is a pattern with the routes of individual measurement
routes due to the low quality of the survey data. Deviations are as high
as ±50 cm and are mainly caused by an inaccurate reduction to the
reference gauge level. Some more causes of a number of inaccuracies was
found with the help ol the survey metadata. Moreover, calculations
yield an average increase of depth of approximately 70 cm within
20years. For the represented area (208.9 km
2 ), this corresponds to a
sediment loss of more than 146 million square metres. Because of the
obvious inaccuracies in the sea survey clata the result of such a sediment
loss is doubtftil.
Profiles vs. average change of depth
Figure 3 shows profiles which were calculated from the grid database.
Despite some oscillations, an increase of depth over time is observed.
Some of the oscillations can be assigned to inaccuracies in the survey
data. Because of the influence of these inaccuracies, the general suitability of profiles to describe changes in the shoreface elevation must be
questioned. To obtain a more reliable picture, average changes of depth
were calculated for various sub-areas of the shoreface extending over
several km
2 (fig. 4). From zones of a certain shoreface elevation (e.g.
-6 to -8 m), average changes of depth towards the most recent survey
campaign were calculated. Compared to the profiles in figure 3, the
influence of inaccuracies is reduced. In figure 4 an almost constant
increase of depth in the shoreface can be observed. Individual survey
campaigns deviating from the general trend can be identified and it can
be concluded that the increase of depth is remarkably larger in the
-6 m to -8 m zone than it is in adjacent, deeper areas. This is a general
observation for all studied areas which cannot be recognized from
elevation profiles of the type shown in figure 3.
225
If available, additional data about each survey, such as reference gauge
levels, measurement techniques, assigned ship, date, and time, were
included into the relational GIS database. During evaluation and interpretation of the results this metadata turned out to be very important.
A systematic influence of different echo-sounding systems was found
with the help of that metadata (fig. 5).
Evaluations and data quality (examples
In this chapter some examples of the methods used for further evaluations
of the GIS database are described. To enable regional comparisons, evaluations were conducted for more than 5 000 km
2 along the shoreface of
the German Bight. All evaluations are based on the same GIS database.
Changes of depth
On the basis of the grid database changes in depth between two different
surveys can be calculated and represented spatially within the GIS.
With these changes of depth mass balances can be calculated for any
area. The result is a pattern with the routes of individual measurement
routes due to the low quality of the survey data. Deviations are as high
as ±50 cm and are mainly caused by an inaccurate reduction to the
reference gauge level. Some more causes of a number of inaccuracies was
found with the help ol the survey metadata. Moreover, calculations
yield an average increase of depth of approximately 70 cm within
20years. For the represented area (208.9 km
2 ), this corresponds to a
sediment loss of more than 146 million square metres. Because of the
obvious inaccuracies in the sea survey clata the result of such a sediment
loss is doubtftil.
Profiles vs. average change of depth
Figure 3 shows profiles which were calculated from the grid database.
Despite some oscillations, an increase of depth over time is observed.
Some of the oscillations can be assigned to inaccuracies in the survey
data. Because of the influence of these inaccuracies, the general suitability of profiles to describe changes in the shoreface elevation must be
questioned. To obtain a more reliable picture, average changes of depth
were calculated for various sub-areas of the shoreface extending over
several km
2 (fig. 4). From zones of a certain shoreface elevation (e.g.
-6 to -8 m), average changes of depth towards the most recent survey
campaign were calculated. Compared to the profiles in figure 3, the
influence of inaccuracies is reduced. In figure 4 an almost constant
increase of depth in the shoreface can be observed. Individual survey
campaigns deviating from the general trend can be identified and it can
be concluded that the increase of depth is remarkably larger in the
-6 m to -8 m zone than it is in adjacent, deeper areas. This is a general
observation for all studied areas which cannot be recognized from
elevation profiles of the type shown in figure 3.
225