The almost annual Sirena sea trials began over 10 years ago. In each of these, the NRV Alliance has towed a two hydrophone array to receive the marine mammal acoustic sounds. This reliable equipment was supplemented with two newer arrays this year and they continue to collect sounds in the water for about 20 hours each day.
The entire array is actually made up of several pieces. First, the tow cable is firmly attached to a winch on the ship (orange in the attached picture). 220m of tow cable trail behind the ship and attach to the actual array – a 15m long piece of tubing, filled with oil in which two microphones (called hydrophones) are spaced 8m apart. The sounds are transferred from the hydrophones as electrical signals through wiring in the oil filled tubing, up the tow cable, through a deck cable and into the laboratory computer. The submerged array stays at about 18m deep in the water when the ship is traveling about 5 knots.
While we continue to test other pieces of equipment (smaller, different features, etc), this array continues to be the Cavallo vincente non si cambia