Mission Profile

Here is a quick overview of the work we will be doing on this mission. This is preliminary, based on my understanding from discussions with the other people, and may be not entirely accurate. I will try to fix it up as we go along.

Transit

First we will steam from Guam to the site of the wreck. This will take about three days or so.

Drop transponders

When we arrive on station, the first task is to drop several transponders (I think eight or nine). These are sonar buoys which sink to the bottom and sit on little anchors. They are yellow spherical things about 2.5 feet in diameter. When we send them a sonar "ping" signal, they transmit another signal, and the time delay gives a measure of distance. These will be used as navigation references for the rest of the operations. This will take less than a day.

Sonar survey

We will use sidescan sonar to make an overall map of the wreck site. (The previous survey generated a rough map, which we have as a starting point, but we will want a more detailed picture.) The sonar sled is towed on a cable, about 100 meters above the bottom, with a fiber optic tether to carry signals to and from the ship. It's about eight feet long, metal frame with stabilizing floats on top.

Sidescan sonar sends a narrow beam sideways from the vehicle (both sides, port and starboard) and uses the echo to get information about the contours of the bottom (in a narrow slice). As the vehicle is towed along, the slice paints a "swath" along the bottom. We will crisscross the site with several swaths, to cover the area of the wreck.

Once we have the sonar data, we need to post process it. (This is my job, or one of them.) The data will be cleaned up and filtered to remove noise and anomalies. The several swaths will be combined into a single map of the site. This process is called "mosaicking" and the result is called a "mosaic" because it's a collage or combination of little pieces, like tiles. All this will take maybe two or three days.

Imaging survey

Next, we will use Argo, one of our Remotely Operated Vehicles (ROVs) to collect visual data. Visual imaging is much more accurate and detailed than sonar, but much more time consuming. While the sonar swaths may be a kilometer or so wide, visual imaging can cover areas only ten to twenty feet or so across. (The water is murky, for one thing, and it's totally dark down there, so Argo has to have its own lights, for another.) It will take several weeks to collect visual data and generate a mosaic.

Like the sonar sled, Argo is towed by the ship, and will crisscross the area, in a pattern they call "mowing the lawn." Argo does have its own manuvering thrusters, which are used to stabilize it, mostly. (The motion of the ship on the ocean waves can pull on the tether and jerk the vehicle around, which is really bad for collecting good images.)

Argo also has its own sidescan sonar, which is used as a piloting aid, data is not collected from this sonar. As is the case with the sonar survey, the data (tens of thousands of images) needs to be post processed and assembled into a mosaic. This job alone will take a week or more.

Jason operations

The really interesting part of the mission begins when we send Jason down. Jason is another ROV, much more sophisticated than Argo. Jason is not towed by the ship, but navigates under its own power, under control of a pilot on board the ship (this is Will Sellers' job, he's my brother in law) with a tether to carry information back and forth. Jason doesn't have sonar, but does have several video cameras for live video, electronic and 35mm film cameras for still pictures, as well as a manipulator (robot arm). For this mission, we have added a high definition black and white camera and a color video camera, for close examination of material at the wreck site. What exactly Jason will do depends on what the first two surveys find. For example, there are plans to do close up examination of the edges of the metal frame (where it broke when the vessel sank), to look for signs of corrosion, metal fatigue, defects, and so on. Jason may even cut loose sections of the wreck and bring them back to the surface for testing. There are also plans to look at the wreck's deck hatches, to see if they are sealed, open, or broken off. The condition of the rudder and propellors, the pattern of dispersal of debris as the vessel sank, all will help determine what went wrong, to help avoid such accidents in the future.

Transponder recovery

Finally, when operations at the site are done, we will recover the transponders we placed at the beginning. When we send them a special signal, they release their anchors and float to the surface, where they can be retrieved.

Transit

We will steam from the site to Yokohama, which will take a couple of days. And there will be much rejoicing.

How this mission is unique

Most of the work that the Deep Submergence Lab (DSL) does is scientific, such as exploration of hydrothermal vents ("black smokers"). This mission, on the other hand, is forensic in nature. That means that the data types are simple (we won't be measuring temperature, magnetics, salinity of the water, and so on) but there is a LOT more data.

The people I'm working with are saying that this is one of the biggest things they've done, in terms of how much equipment we have to bring aboard and install, and how much data will be gathered. There are pallets full of video tapes, data cartridges, and video disks ready to be used, and a full shipload of people to do the work.

This page maintained by Wil Howitt
Last updated 30 March 98