| Statement |
Three of the five dedicated surveys of the Cromer Shoal Chalk Beds rMCZ were commissioned to collect acoustic data. The first acoustic survey was undertaken during March and April 2012 by Titan Environmental Surveys Ltd on board the survey catamaran Titan Endeavour. A Geoacoustics Geoswathe system was used to collect detailed swathe bathymetry and acoustic backscatter data. Processing of the bathymetry data was carried out using the GeoSwath processing suite, GS+ 3.50. This survey targeted the foreshore area designated as Priority 1 for survey and partially covered the Priority 2 area, at its western extent (Jenner, 2012). The second acoustic survey was conducted by Cefas in January 2013 on board the RV Cefas Endeavour. This survey was originally intended to collect full coverage acoustic data from the entire site. However, due to time and weather constraints, this survey targeted the site area further offshore, to the north east of the site, and survey lines were conducted with a larger-than-intended line spacing of approximately 320 m (Ware, 2013). Multibeam bathymetry and backscatter data were acquired using the Kongsberg EM2040 system, operated at 300 kHz. Multibeam echosounder (MBES) data were processed using CARIS HIPS software. Backscatter data were processed with Fledermaus Geocoder Toolbox. The final acoustic survey was conducted in February and March 2014 by Gardline Geosurvey using a hull mounted Kongsberg Simrad EM3002 system on board the MV Confidante. Data were processed using CARIS HIPS/SIPS with fina lvisualisation deliverables processed with QPS Fledermaus. This survey targeted the Priority 3 area of the rMCZ (Januszewki, 2014). All bathymetry data were collected and processed in accordance with the International Hydrographic Organisation (IHO) Standards for Hydrographic Surveys - Order 1 (Special Publication 44, Edition 4).
Stations were selected for grab sampling if suitable sublittoral sediment was observed in at least 50% of the seabed images collected. Stations were avoided if rocky habitat and/or delicate epifauna were observed. Generally, a position fix from the mid-point of the drop camera survey line was used as the target for grab deployment. However, if a mixture of habitat types was observed during the camera transect, the most appropriate target position was chosen. A mini-Hamon grab, with a sampling area of 0.1 m2 , was deployed from the stern gantry of the vessels to collect sediment from the seabed, as described by Ware and Kenny (2011). Sampling positions were recorded using HYDROpro data acquisition software when the gear contacted the seabed. Once recovered, the sample was emptied into a suitable container, photographed, and the sample volume measured. A sub-sample (approx. 500 ml) of sediment was removed for particle size analysis (PSA). The remaining sample was washed over a 1 mm mesh sieve, photographed and preserved in a buffered 8% formaldehyde solution.
ArcGIS was used to perform an initial unsupervised classification on the acquired backscatter image. The single band backscatter mosaic was filtered and smoothed prior to the application of an Iso cluster/maximum likelihood
classification routine. Python scripting language was used to automate the workflow.
The vectorised output of the semi-automated process is reviewed manually to assign sedimentological classifications in accordance with the EUNIS habitat classification system. An appreciation of the geological characteristics of the area also means that the analyst can ÔÇÿsense checkÔÇÖ the outputs. Polygons can be amended, modified and merged to best represent the acoustic data, groundtruthing samples with the influence of geological judgement. The newly acquired acoustic data covered approximately 78% of the site area, mapping was therefore restricted to this area only. |
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