May 13 2008
May 13 2008
This morning’s beautiful sunrise, one of the perks of the night shift! (photo by Dann Blackwood).
Marshall Swartz and Dann Blackwood make the final checks before the towcam is deployed.
It’s been a great day on the Nathaniel B.Palmer. We just finished the second Towcam flight. I call it a flight because it gently flies over the seafloor and takes digital photographs every 10 seconds. It is launched and recovered from the sea by a large hydraulic winch linked to around 7000m of steel cable. The path the Towcam travels is totally controlled by the ship’s motion, the bridge crew carefully move the ship about a quarter to a half of a knot per hour to get continuous photographic coverage for up to 5 hours at a time. From just these first two Towcam flights we have over 3000 images of the seafloor. While trawls and dredges bring samples up from the bottom, the Towcam shows us how these rocks and fauna exist in their environment. The images allow us to see what animals are present and how they are living. It also shows us what the seafloor itself is like, whether it is covered in sediment or rocky. When controlling the Towcam, we try to keep it around 4m off the seafloor to provide quality photos. To help us analyze the photographs, there are three green lasers that shine on the sea floor to provide a sense of scale in the photo.
The Towcam weighs in at about 1000 pounds, but it is relatively easy to control. However, in rough weather the pitch and roll of the ship can cause the Towcam to move up and down from the seafloor making it difficult to take good photos. Above 7 m from the seafloor, the strobes can no longer illuminate the bottom, but conversely if you go too close you run the risk of crashing Towcam into the seafloor. So, the pilot has to keep a close eye on the instruments and a steady hand on the winch control to ensure high quality photographs and the safety of the Towcam.
The actual camera of the Towcam is cradled in the middle of the aluminum frame and points straight down. We have two cameras on board each configured to handle different lighting situations, so we have to take an educated guess as to the reflectivity of the seafloor. There are two big downward facing strobe lights, one in the front and one in the back. All the systems are powered by four large oil filled batteries that are designed to work under water and under large amounts of pressure. These batteries are enough to power all of the Towcam’s sensors and camera for up to 6 hours. In the middle of the frame is a CTD which stands for Conductivity, Temperature and Depth sensor. The CTD continually measures the water conditions around the Towcam and sends us data back up the cable about how deep the Towcam is. In addition, there are sonar ranging altimeters mounted on the front and back to tell us precisely the distance between the Towcam and the sea floor and to tell us if we’re about to collide with something. All the data from the CTD, altimeters and how often the strobes are firing are logged on a computer for the whole time it is in the water. The big white fin on the back acts like the feather on an arrow to keep the Towcam pointing in the right direction.
The grey tubes on the top of the Towcam are water sampling bottles which are deployed with their end caps held open. When a sample is needed at a particular location or depth, an electrical signal is sent down the cable that trips a switch holding a lanyard that releases the end caps, which snap shut. There are six of these five-liter bottles, each of which can be fired individually by the Towcam pilot when needed. The water samples collected from this trip will be analysed by Laura Robinson, Tina van de Flierdt, Taryn Noble and Kate Hendry for nutrients, carbonate chemistry, stable isotopes and radioisotopes.
Towcam was created by Dan Fornari, Marshall Swartz and other members of Woods Hole Oceanographic Institution. We look forward to more successful Towcams in the future!
Dann Blackwood and John Swartz
Towcam in full glory, being deployed into the water.
After a successful deployment the towcam is brought back onboard.
A picture taken from 500m depth on the seafloor of the Antarctic Peninsula.
This octopus and shrimp were spotted at 2000m.
What are the purple things in the top right hand corner? They are this purple soft coral called Bayergorgia.
Recognise this coral from the seafloor? This is a soft coral called Thouarella both in life and after being collected by a trawl.
Marshall Swartz plans the Towcam deployment using multibeam data collected by the Nathaniel Palmer.
Kate Hendry and Tina van de Flierdt sample water collected by Towcam.