Data Acquisition and Processing Report (DAPR) - Center for Coastal ...

The EM1002 sonar system is controlled with a UNIX based operator system
(SUN Solaris 8) that utilizes the Common Desktop Environment and Kongsberg’s
MERLIN V 5.2.2 acquisition and control program. Before surveying commenced and
periodically thereafter, the EM1002 system self-test (BIST test) was performed to
confirm the sonar’s operating status. Sonar errors were not observed during the survey.
As per advice from the Kongsberg representative during the SAT, the automatic and
default parameters were used to control the sonar during data acquisition. The EM1002
backscatter default options were verified with Adel Sterling and the Hawaii Mapping
Resource Group who have extensive experience acquiring backscatter imagery with the
EM1002 system onboard the R/V KILO MOANA. The equidistant beam spacing mode
was chosen to give a uniform distribution of soundings on the seafloor. The ping rate
was set by the system and was automatically adjusted according to the depth below the
transducer. Only limited runtime parameters changed during the survey including the
maximum port and starboard angles, which did not exceed 60°.
A Reson 7125 multibeam echosounder was mobilized for this cruise to map the
shallow water habitats in water depths of less than 75 meters. The system was mounted
from the moon pool flange of the NANCY FOSTER. The 7125 is a dual frequency
system (200/400 kHz) that measures water depths across a 128° swath, consisting of 512
individual beams. The sonar was set to a maximum ping rate of 50 Hz. The ping rate
was reflected by the range scale set by the operator of the sonar, the shallower the range
scale, the faster the ping rate. A variety of ranges were used during acquisition, however
the 100m range or less dominated the majority of survey. A spreading loss of 30 log
decibels and absorption value of 50 decibels per kilometer were used as general values
recommended by Reson for working in seawater. The power was maintained at 220dB
and the gain varied between 33dB and 50dB. The sonar data (snippets and bathy) was
collected via ethernet with Reson PDS 2000 acquisition software. Unfortunately the
7125 did not operate as developed. Reson provided a sonar technician for the cruise and
she was unsuccessful in determining the reason behind numerous data quality issues
during the survey. These
issues included dropped pings,
beam steering inconsistencies
and wrong swath widths
reported from the sonar to the
topside unit. Fortunately the
data still meets the IHO
requirements for the survey.
These issues will be described
thoroughly with an explanation
from Reson in Appendix L.
Versions of all hardware and
software used for this survey
can be found in Appendix B.
Fig 3: 7125 Mulibeam w/moon pool flange mount
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