Matt Fowler, Research Assistant / Marine TechnicianThis post comes to us from Matt Fowler, Research Assistant and Marine Technician:

With the assistance of the U. S. Coast Guard, we deployed the Full Ocean Depth Hydrophone (FODH) at Challenger Deep, in the Mariana Trench. Challenger Deep has the greatest ocean depths known to exist on Earth. As the technician responsible for this deployment, I had a unique perspective as I observed the launch and descent of the FODH.

We had great weather during the two day cruise, just behind one typhoon and ahead of a second one. Perfect timing gave us a great weather window with a cool, calm 10-15 kt breeze and a gentle 3m swell for our otherwise sweltering 100 degree, 100% humidity deck operations. Overall, everything went well and the hydrophone was successfully deployed. The drop site, ~ 1 km NE of where we wanted it to land on the seafloor was chosen based on the little information we had regarding the deep-sea currents at Challenger Deep.

Top pair of floats going in.
Top pair of floats going in.
Full Ocean Depth Hydrophone and RBR
Full Ocean Depth Hydrophone and RBR














After the anchor was dropped, and our instrument began the long descent to the bottom, I was alone, tracking, as it slowly sank into oblivion. With my trusted acoustic ranging deck-unit at my side, I was constantly obtaining updated depth information every 20 seconds during the nearly 9 hour journey to the seafloor 6 miles below.

Somewhere about 8000m I realized the hydrophone was close to 25,000ft and still had a long way to go. As I continued to observe the descent, I flashed on the movie, “The Abyss” and the scene with Brinkman on his way to the bottom and his friends tracking his descent… I kept waiting for Big Geek to implode…

Deck unit reporting a depth of 8181m.
Deck unit reporting a depth of 8181m.
Deck unit showing a depth of 9460m and still going...
Deck unit showing a depth of 9460m and still going…

As the ‘phone passed 9000m, I realized it was approaching 30,000ft depth, and still going! I was far more interested in the 20 second updates with each new depth presented 3 times a minute, when I realized the hydrophone was deeper than the 8848m, Mount Everest is tall… AND STILL GOING! Hopefully, 2000m deeper!



Challenger Deep Screen Shot July 2015
After an 8hour, 40 minute descent, the hydrophone ended up on the bottom, about 600m N of our target. We won’t know the exact depth until we obtain the depth recorder with the mooring later this year, but based on the best bathymetry available, we may be deeper than 10800m or 35325ft. More than 6.5 miles deep! If all goes as planned this will be the deepest moored hydrophone data ever obtained.

After recovering the FODH on a subsequent cruise, we will find out soon if we were up to the “Challenge” of Challenger Deep.



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