2019-12-16 GC Agenda - Item 5 - Attachment 1 - Noosa Spit Shoreline Erosion Management Plan-Part 2

Backscatter Data
Although backscatter data wasn’t a focus of this project the data were logged and selected
regions processed to create mosaics. The sidescan-type backscatter data produced by the
ET6205 provide finer detail of riverbed features than the bathymetry data, and can be used to
make inferences about seabed types (e.g., the bathymetry was gridded at a 50cm bin size
whereas the sidescan sonar data was gridded at a 10cm bin size). In general, finer sediments
that absorb signal strength appear as darker pixels and coarser sediments that return more
signal appear as lighter/brighter pixels.
The example below comes from an area along Hilton Terrace. The sidescan imagery extends
to the shoreline and shows a rock-strewn area amongst softer sediments. In this case the
mosaic doesn’t show pronounced changes in backscatter strength, but the textural
information suggests may be used to show more cemented or consolidated areas relative to
soft sediment areas.




              Figure 21: Example backscatter mosaic along Gympie Terrace shoreline.



A more extensive analysis of the backscatter data is intended prior to further geophysical
work involving a subbottom profiler (SBP) system. The SBP data should allow identification of
sand regions in advance of a dredging program.




22                             Noosa Council - Noosa River Survey                     20.06.2019