standardization of environmental data and information - International ...

?? Classification of facies types should be verified by looking at their
surface with a video system.
?? Samples should be gathered and tested onboard for various
properties.
?? Finally, laboratory testing and modelling should be conducted.
In conclusion, he suggested that the large-scale and sediment
parameters he had described be used also as an environmental framework
for defining the benthic communities.
SUMMARY OF DISCUSSION
Sonar mapping anomalies
A participant from the Korea Ocean Research and Development
Institute (KORDI) said his organisation, using a 12 kHz side-scan sonar
system on a manganese nodule field, had found a substantially higher
backscattering strength than Wiedicke had reported. This was a standard
frequency used in Hydrosweep and many other deep-water systems. As
KORDI had generally found a greater abundance of nodules, his people had
thought at first that this might be due to reflection from the nodules
themselves. Another possible explanation, however, was that, because the
wavelength at 12 kHz was much bigger than the nodule, the effect might be
due to the physical property of the substrate 10 or 20 metres below the
nodules; thus, besides a reflection directly from the nodules, it was also
coming from the upper substrate.
Wiedecke-Hombach replied that similar observations had been
recorded in the Pacific Ocean with other kinds of side-scan sonar systems;
strange features had been found that could not be observed on the surface.
The effect had been ascribed to interference of the signal wavelength and
its penetration into the uppermost sediment layer. A side-scan sonar
system should be geared to the particular target; with small nodules, higher
frequencies might have to be used so that nodule distribution would not be
confused with sediment properties.
164 INTERNATIONAL SEABED AUTHORITY