Coastal zone mapping 
26 
Hydrographische Nachrichten 
Use of læer bathymetry 
at the German Baltic Sea coast 
An article by WILFRIED ELLMER 
The German coastal waters are quite shallow. The idea arose to use airborne laser 
bathymetry (ALB) for hydrographic surveying of near-shore areasof the German Baltic 
Sea. Sncethesewatersare relatively turbid, it became necessary to investigate to what 
extent modern ALB systems could be of practical use in an area large enough for hy 
drographic purposes especially in the Baltic Sea. The basic questionsto be answered 
bythe project were: Which areascan be measured bythismethod?And how expensive 
will thisbe in relation to traditional methods?Ffom 0 to 0 ,fourtestsurveyshave 
been accomplished in 
an area north of the city ALB| laser bathymetry | Baltic Sea | Sbcchi depth 
of Wismar. During these 
surveys, many relevant 
questions were solved. 
Author 
Dr. Wilfried Blmerisdeputy 
head of the surveying and ge 
odesy section of the German 
Maritime and Hydrographic 
Agency (BSH) in Fbstock. 
wi If ried .ellmer(Sbdi .de 
1 The state of hydrography 
in Germany 
1.1 Hydrographic surveying in Germany 
The German Maritime and Hydrographic Agency is 
mandated to conduct hydrographic surveys in the 
coastal waters and the EEZ of two di erent areas: 
• North Sea, there are very busy approachesto 
Hamburg, Bemerhaven, and Wilhelmshaven, 
with large shallow areasshaped by strong 
tidal currents, the \Afodden Sea area Dueto 
these currentsthe water is very turbid, large 
partswith Secchi depthsof lessthan . m. 
The depthsof shallow areas are changing very 
much, so they have to be resurveyed very 
frequently, partly every year. The deeper areas 
of up to m are to be resurveyed once in 
years only. 
• Baltic Sea, also quite shallow, up to 50 m. The 
tidal range is lessthan cm, so the structure of 
the bottom is much lessdominated by strong 
currents Most parts will be resurveyed once 
in or yearsonly, but it is necessary to 
achieve full bottom coverage. The visibility of 
the water is much better than in the North Sba, 
sometimes better than m. 
Sjrveying isdone by single-beam and multibeam 
echo sounding. In areasof frequent resurvey activ 
ities, single-beam echo sounding is the standard 
procedure. 
Week search isavery important taskin German 
waters The obstructions database contains about 
, positions E/ery year nearly new obstruc- 
tionsare found, and positions have to berevis- 
ited in order to examine changes of the position 
and the least depth; espedally in the strong tidal 
currents of the V\fedden Sea, one has to take into 
account that even large objects may move. 
1.2 The question of 
airborne laser bathymetry 
In former times, airborne laser bathymetry (ALE^ 
was assumed to be unsuitable for hydrographic 
surveys in German waters due to the poor water- 
visibility conditions A test ight in showed 
poor results, and seemed to validate this assump 
tion. However, recent developments of new ALB 
systems may lead to better results, and made it 
necessary to investigate the potential of thistech- 
nology, and to verify, whether or not ALB has the 
potential to replace the traditional techniquesorat 
least to complement them. 
A project was started in order to answer this 
question, and to decide on further actions The ba 
sic questionsto be answered bythe project were: 
• Wiere does it make sense to use ALB for hydro- 
graphic surveys? 
• How expensive will thisbe in relation to tradi 
tional methods? 
The criteria for these answers are those of & 
(I HO ). 
2 The laser bathymetry project 
2.1 The structure of the project 
The project took place in the years to 
Each year one ight was planned and a call for 
tender was issued. The area to be surveyed was 
chosen north of the island of Fbel, an area with 
di erent structures, with some stones, and with 
depths from zero to a depth well exceeding the 
capabilities of modem ALB in order to reach the 
system’s maximum depth capability. 
The Institute of Fhotogrammetry and Geo- 
Information (IH) of Leibnitz University of Hannover 
took over a scienti c cooperation in the frame of 
the project. One person processed the ALB data 
and prepared a report (Niemeyer et al. ). Ad 
ditionally, some Bachelor and Master theses were 
written on special aspectsof the project. Attached 
to the project a board was installed with repre 
sentatives of some other German institutions in 
terested in that topic. The board met every year to 
exchange information on the project and on other 
activities pertaining to ALB Cbastal protection au 
thorities were especially interested in the project 
and gave input on their activities (Christiansen 
). This was very important since ALB cam-