Journals 2003/2004

Sarah Quan
Narragansett High School, Narragansett, RI

Direct measurement of currents can be made in two ways: using the Eulerian method or the Lagrangian method. The Eulerian method collects data from a fixed point as the current passes by. Using the Lagrangian method a device collects data as it flows with the current. This method allows you to track the movement of a parcel of water. This study will utilize the latter method where the sound source will be moored and the RAFOS receiver will float freely in the current. We deployed the first RAFOS float today. The RAFOS float was developed by Dr. Thomas Rossby (the same Dr. Thomas Rossby with whom I'm on this cruise). It consists of a closed-end glass tube that is about 1.5 meters long. The glass is a borosilicate, the same material used in pyrex, which will not expand or contract with changes in temperature insuring the float will maintain a constant volume. Constant volume is important because the float needs to be neutrally buoyant on a specific density surface. The float contains a hydrophone so that it can listen to the "pongs" from the moored sound sources. It also contains a satellite radio antenna so that it can transmit data when it surfaces. Before a RAFOS is deployed its internal clock is calibrated and adjusted for the appropriate mission length. The six RAFOS we are deploying on this cruise have a mission length between 30 and 90 days. The short mission length is to insure that the system is working. After that point an additional 60 RAFOS will be deployed; 30 by the Marine Research Institute in Iceland and another 30 by the Marine Science Center in the Faroe Islands. These floats will have a mission length closer to two years.