Ocean acoustic sensor installation at the South Florida Ocean Measurement Center

A tri-axial array of acoustic hydrophones has been installed off the South Florida coast in 145 m of water. The installation is one of a number of projects that have begun making use of the new South Florida Ocean Measurement Center facilities in Dania, FL. The arrays are linked to shore via a fiber-optic cable and powered from shore with a separate insulated copper cable. Two of the arms of the array are deployed on the bottom to the east and south of the origin. The third array is a sub-surface vertical mooring which includes a pressure sensor to monitor the depth of the top buoy. Each axis contains 32 hydrophones spaced in a nonlinear distribution to facilitate acoustic coherence measurements. Other sensor configurations are possible, including the replacement of hydrophones with other instruments such as current meters or temperature, pressure, or conductivity sensors. Small projectors are placed at the base of the vertical array and at the ends of the horizontal arrays, making it possible to determine the location of each sensor in real time via time-of-flight measurements. Computers running the Linux operating system control the projectors and process data from each leg of the array. Each of the three computers is connected via fiber-optic lines to a Fast Ethernet switch box and networked to shore. The computers can be accessed via TCP/IP connections and programmed from shore to suit new missions. A wireless link to the Nova Southeastern University network and the Internet makes it possible to access the system and conduct experiments from anywhere in the world. The current mission of this system is to study the coherence of shallow-water acoustic propagation. However, knowledge gained here will facilitate a variety of future projects-which include active and passive sonars, ambient noise study, high-frequency acoustic monitoring of fish migration, and acoustic tomographic monitoring of the Gulf Stream. Excellent data were obtained from several experiments. At the present time, only the vertical array is working but plans to restore the two horizontal arrays are actively pursued.