Friday, March 20, 2015

Chagos 3.0 - Day 4

Day four, and we’re racing through our servicing work with 44 of 48 sites visited already, thanks to the support of a great crew on Vava and some of the calmest weather we’ve seen in Chagos. With flat seas and hardly a breath of wind, finding our monitoring equipment is proving easy, and the boat and diving work is a true pleasure!

Most of our monitoring array here is made up of submerged VR2W type acoustic receivers, which require diving on, but with new units ready to go in the water it take a two person team only minutes to remove the cable ties and hose clamp fastening the receiver to the mooring line, and fix the replacement in its place. We would probably all rather the dives took longer as there is always something to distract us down there, whether it is schools of fusileers circling you on a reef wall, or a carpet of garden eels stretching away across the sandy bottom of one of the channels.

Vava’s bosun, James, puts the finish touches
on a newly installed VR2W receiver
The other two types of receivers used in the Chagos array require very different approaches. The latest addition to the array in 2014, the four VR4-UWM (standing for UnderWater Modem) can be ‘talked’ to directly from the boat using a portable acoustic modem that instructs the unit on the seabed to transmit its data up to the surface. By holding station over or near the receiver, we can retrieve our data without even getting our feet wet!

Dr. Taylor Chapple enjoying some time
out of the sun while he downloads
 one of the Chagos underwater modem receivers
The last type of equipment used out here are our two VR4-Globals. These, as the name suggests, give us access to our data from anywhere in the world through an Iridium uplink build into a surface unit, connected to a hydrophone hanging below. The whole thing is fitted into a buoy that can be anchored in strategic positions to give us live data on shark detections. These are by far the most complicated to service, requiring a team tackling the surface components to coordinate closely with divers working on the hydrophone and cable. Add a ripping current and it makes for a challenging job, but it’s worth the effort to get real time feedback from our tagged sharks when we are back at our desks.

Taylor gets to work on the transmitter…
…while the dive team are busy below

With the vital servicing work nearly complete we are focussing the majority of our effort on catching and tagging sharks. More on that tomorrow.
   -Dave Tickler

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