East Anglia Offshore Windfarm: Zonal Environmental Assessment Benthic Report
B.3 Seabed Imagery Acquisit ion and Assessment
B.3.1 Seabed Imagery Acquisition
Seabed imagery was targeted at 107 camera and grab stations across the EAOW zone, of which 82 stations were additional stations allocated as a result of CODA streaming of acoustic data. Video imagery and multiple still seabed images were acquired from each of these stations.
The positions of al l stills and th e start and end positions of a ll videos were recorded using dGPS with a nominal accuracy of 2m. All imagery was obtained using an underwater camera with a freshwater lens; this is a bespoke system developed specifically for obtaining images in turbid, low light conditions such as those encountered in the North Sea.
During deployment the c amera was sl owly lowered to the seabed whilst the u mbilical was tied to the wi nch wire at 10m i ntervals to prevent the cable from being pulled out by currents creating potential health and safety hazards. Once the camera reached the seabed, recording commenced, a fi x was taken and still images with fi xes were taken as the camera moved across the seabe d. Following capture the quality of each image was checked and re-sampling was undertaken where necessary.
Between 5 and 10 i mages and 5 and 10 minutes of vi deo were taken during each camera deployment. Examples of the seabed imagery acquired during the surve y are presented in EAOW GeoPDF.
Detailed observational notes were m ade on the character of the sedi ment and fauna witnessed for each sti ll image. These notes were entered into the s urvey log book and checked for consistency. The seabed imagery field notes are shown in Appendix Table 4.
B.3.2 Seabed Imagery Analysis
The seabed imagery acquired during the survey was i nspected on the ve ssel in ‘real time’ in order assess the pres ence, or otherwise, of important benthic habitats a t stations which were indicated as being of
possible importance following the completion of the ecol ogical geophysical review. Where potentially important habitats were discovered the seabed images were used to position the vessel at the fri nges of the habitat before grabb ing commenced. Following the compl etion of the fi eld operations the seabed images were reviewed in order to assess the status and importance of any ecologically sensitive habitats such as Sabellaria reefs.
