The 2002 season for Sound in the Sea has begun and we face the same challenge faced by ocean explorers throughout the centuries: foul weather! We are on the French research vessel, Le Suroit, which sailed from Ponta Delgada in the Portugese Azores on Saturday, May 18^th and plan to deploy six underwater hydrophone moorings in the North Atlantic to explore the region acoustically.  Although not in the path of any large storm, the westerly winds have been sustained at 25-35 knots for the entire period building up sea of 5-8 meters.  Le Suroit is relatively small (52 meters, or 160') so that we are being tossed about.  Last night we recorded a 35 degree roll. In spite of the weather, we have succeeded in deploying three moorings already and are enroute to the fourth site.

As we sailed from the Azores, we spent a few hours mapping some of the volcanic features of the Azores using the ships EM300 multibeam mapping sonar.  Portugese geologists onboard have been compiling a map of the Azores based on similar opportunities from multibeam capable vessels.  We also have been sighting marine mammals for comparison the hydrophone records and encountered a large pod of mixed fin whales and blue whales near the Azores. Rita Bento, a student at the University of the Azores who has been working with Sound in the Sea, is on board to record such observations.

The team and the effort are truly international. The French government, through its ocean agency IFREMER, are providing all of the ship time and support.  We have four French earth scientists on board, including Dr. Jean Goslin of the Universite de Bretagne Occidentale in Brest, who is our Chief Scientist for the mission.  There are three technicians provided by IFREMER to operate the multibeam sonar.  Besides the three Portugese scientists already mentioned, and myself (American), Dr. Haru Matsumoto, our senior engineer from Sound in the Sea is here and is a citizen of Japan!  NOAA’s Ocean Exploration Program is supporting our participation including the costs of constructing the hydrophone instruments.

The procedure to deploy a hydrophone mooring is as follows: We must first identify an area of the seafloor which is relatively flat for 5 - 10 km diameter. This is necessary so that we can be certain of the length of mooring required to suspend the hydrophone into the overlying SOFAR channel.  Once a site has been identified, we measure the water properties using an eXpendible BathyThermograph (or XBT) and determine the precise depth of lowest sound speed (the axis of the SOFAR channel).  Knowing the water depth and the depth that we want to suspend the hydrophone, we can construct a mooring of just the proper length.  Next we position the ship downwind 3-4 km and begin slowly moving toward our desired deployment site as we pay out the mooring into the water.  First a large yellow float, with strobe light, flag and floating line to aid in the eventual recovery of the mooring next year.  Then the hydrophone instrument, which has been checked out onboard and programmed to begin recording usually the next day. Next 2,500 -4,500 meters of special mooring line design not to stretch or vibrate (strum).  Finally, an acoustic release device that can be commanded to release the mooring and a large anchor composed of surplus aircraft carrier anchor chain.  When the ship reaches the desired point, the anchor is released and the mooring in sent to the bottom to record for a year until we return to pick it up.  The final procedure is to acoustically “ping” to the release above the anchor from various directions to determine it’s exact location.  This effort has been especially difficult this year due again to the high seas which make the ship less maneuverable and generate significant acoustic noise into the environment.

So far, we have deployed the two hydrophones closest to the Azores and the middle hydrophone on the western side.  We are now steaming north to deploy the northwest instrument.  This order is different that the original plan, but due again to the westerly winds, we did not want to have to transit east to west more than once!  I will file another report on the way into France next week.