Tuesday, July 17, 2012

Geomorphology/Shallow Shelf Seafloor Mapping Cruise - July 2012

DAY 7 (July 17, 2012) 

1330Z – our final survey day arrives and all is well. We are heading for the C transect off Choctawhatchee Bay which we will survey going northward. The systems have been running remarkably well. 

A little insight on the behind-the-scenes technical issues. I noticed a small calibration issue with the pressure sensor that gives us depth of the towfish. The way we know total water depth for accurate bathymetry is to combine the towfish depth with the depth measured below the fish that we get from the sidescan. As we are using GeoDAS acquisition software from Oceanic Imaging Consultants I have corresponded with them to confirm we can make any adjustments/calibrations to the data in post processing, they have a handy utility built into the acquisition software just for this. Good thing we have internet on the boat now days. We will do other calibration checks later today when we run a “patch test”. The patch test is a small survey of crossing lines that shows us the alignment of the heading, pitch, and roll sensors in the towfish. Why? – all this allows us to plot the imagery in the correct location on a map. Enough technical. 

Seas are 1-2 ft, with whitecaps. 

We passed south of these high-relief mounds near the Madison Swanson Marine Reserve. Dark is strong return and the white areas are shadows behind the mounds.

The north-south distance across this single swath is 500 m. 

Our final student guest blog comes from Anastasia Nienow, Valdosta State University. 

“I don’t think I was home for a full month before I found myself on the Bellows again. So far out of all the trips on the Bellows (once before with Stan and several times with Dr. Snyder) this one is the most relaxing. Most of the time on watch is spent watching the computer to keep an eye out for paleoshorelines and to make sure that data is still being recorded. The only difficult thing to do on watch is to make sure that the cable is placed neatly on the winch. Off watch I mainly read, trying to put a dent in my list of books to read. The Bellows feels less “cozy” this trip since there are only 8 scientists on board instead of 10. I think this cruise has spoiled me for any future cruises with Dr. Snyder’s group. –Anastasia” 

Thanks for going again Anastasia! – I really needed an experienced hand. 

Actually, that’s Alex operating the C3D winch.
2030 UTC – We finished the C transect about half an hour ago and slowed to recover the C3D sonar. After putting equipment in the water and towing it around the Gulf for a week you hope that everything comes up in one piece. That cables aren’t beat up and nothing came loose. Also, sometimes the most dangerous part for the equipment, and people, is getting it back on the deck safely with the boat rocking around. We were recovering in 2-3 ft seas, so the Bellows was moving, randomly heaving 2-3 feet and rolling. As soon as the fish is lifted out of the water it starts swinging and we have to move quickly to snag it and get it on deck. It requires a lot of teamwork. With Captain Boomer and Dave on the 01 deck holding the ship steady, moving the A-frame in, and controlling the block our cable runs through, Alex on the C3D winch controlling the C3D cable in/out (all these are moving and need adjusting together), Shane and I on a tag line snagging the towfish, and Ryan standing by, we landed the fish safe and sound!

The C3D sonar home on deck.

Anastasia and Alex cleaning up.

Raising the tracking hydrophone.

Final track line coverage. There is a method behind the weird pattern.

Post Author:
Dr. Stan Locker

No comments:

Post a Comment