May 7, 2010

TowCam - The Right Tool

TowCam – the Right Tool for the Job Exploring the NE Lau Basin
Bob Embley

The state-of-the-art maps we make using the R/V Kilo Moana’s hull-mounted sonar systems provide us with a great view of the major seafloor features such as volcanoes and fault zones. However, even the best maps of the seafloor require interpretation that is limited by the resolution of the map (the maps we have out here have data points about every 25 meters (~85 feet). Although we can make basic interpretations using these maps such as the presence of hard rock and the type of seafloor landforms, we still have to have images of the seafloor to make finer observations such as composition of the seafloor and the seafloor biological communities. Robotic vehicles and human occupied submersibles are being increasingly used to provide this need but they are expensive and difficult to deploy on short notice. Another lower tech yet very effective way to image larger areas of the seafloor is the deep-towed camera.

Preparing the TowCam for deployment from the stern of the R/V Kilo Moana (left to right: Justin Smith, Susan Hannemann, Ken Feldman). The large fin stabilizes the fish during towing. Orange objects are batteries used to power the digital camera strobe.

The “TowCam” we are using is one of several designed and built at Woods Hole Oceanographic Institution by D. Fornari and M. Schwartz for use by the scientific community. It has evolved from earlier systems developed in the 1960s and 1970s to locate hydrothermal vents and to photographically map the seafloor. The well-designed TowCam includes a digital camera, a light strobe, a sonar designed to monitor the height of the sled off bottom which provides warning of steep topography along its path, a pressure gauge to record depth, and various other sensors to precisely measure temperature, water turbidity etc. The “TowCam” also has six bottles that sample water over hydrothermal vent fields. These instruments are all mounted within a sturdy frame to protect them from accidental contact with the seafloor. The entire system is connected to one of the ship’s deep-sea cables and lowered to about 15 feet off the seafloor where it is towed at slow speed (1/4 knot) over features of interest. The slow tow speed is critical for maintaining maximum control of the camera and ensuring a high spatial density of photographs. On this expedition we have been collecting 2000 high resolution photographs, snapped every 10 seconds over a tow path of about 2 miles.

TowCam photograph of coral hanging on for dear life on unstable volcanic slope of Mata Fitu volcano. Depth approximately 2440 meters (~8000 ft.). Two green dots just above coral are lasers with separation of 15 centimeters (~6 inches).

The progress of the camera is monitored by the scientists on the ship. On this trip we are dependent on the technical expertise of Ken Feldman who has not only kept the system operational but is a master at “flying” the camera near the seafloor using the ship’s winch. Susan Hanneman has volunteered her long expertise and enthusiastic support of the TowCam operation on this expedition and we are also dependent on the expertise of Susan Merle to provide the detailed seafloor maps of the camera tracks.

Scene in lab of Kilo Moana during TowCam operation. Front: Susan Hanneman (left) and Ken Rubin (right) Back: Ken Feldman (left) Craig Harvey (right). Large monitor displays seafloor map of area being towed and control for winch is seen just to left of Ken Feldman.