EK60 Water Column Sonar Data Collected During PC1003

2010 ME70 Workshop (PC1003, EK60). The third leg of the 2010 SEAMAP Reeffish Survey, PC 1003, was originally scheduled as an experimental multibeam sonar workshop. However, on July 12, 2010, FSV Pisces was directed to participate in the response to the Deepwater Horizon (DWH) oil spill by monitoring the area around the well head using Simrad EK60 echo sounders while pressure testing of the cap installed on the well was conducted. This testing period was expected to last for 24 to 48 hours, after which the scheduled workshop would commence. Pisces monitoring effort was later extended and continued through July 20, precluding completion of almost all of the multibeam sonar workshop objectives.

Pisces departed Pascagoula at about 1800 CDT on July 14 and proceeded toward DWH. Clearance to begin operations near DWH was received at 2230 on July 15 and survey operations began at 0000 on July 16 and continued until 0000 on July 20 after which Pisces returned to Pascagoula. Acoustic surveys using Simrad EK60 split beam echo sounders at 18, 38, 120, and 200 kHz and ME70 multibeam echo sounder at 70-120 kHz were conducted along transects spaced 0.1 run apart in the area around DWH. The survey was completed in rectangular areas using north-south and east-west transects at ranges from 1500 m to 2.5 run from DWH. At ranges within 1500 meters of DWH, a free-form survey was conducted to maneuver around other ship traffic and stationary platforms and cover as much of the space around the well head as possible including a large number of passes directly over the well. Data were also collected along transects running from southwest to northeast in an area northwest of DWH where earlier seismic measurements had shown fault lines below the VERTICAL LOCATION > SEA FLOOR running in generally that same direction.

During the survey, the echo sounder systems were used to observe a number of sonar targets that are assumed to be locations where methane or other gas bubbles are being released from the seabed. These are known to occur naturally in this area and most of the observations can be attributed to natural seeps. Similar observations were made intermittently directly over the DWH well head and appear to indicate gas that was escaping from the well. Other sonar targets observed are believed to be riser pipes, ROV tethers, and other equipment associated with the DWH response activity as well as sunken wreckage of the DWH platform on the VERTICAL LOCATION > SEA FLOOR.