October 1, 1998. It's an exciting time to be on board the ship. After a week of loading boxes, setting up computers, deploying transponders, and mapping transects, the data are finally pouring in.
At 4:00 this afternoon, Debbie Smith gathered us around a print-out of the sonar images from the first swath. Volcanic features on the ridge that were not apparent on the bathymetric maps leapt out of the sonar map. Laura Kong pointed out numerous volcanic cones with well-defined craters packed along the top of the ridge. Everybody was happy. As more data come in, they will be processed, put on the computer, and made available to all the scientists on board. Each scientist will then be able to identify features of the ridge they want to study in more detail.
The night before, we attempted what is called a crossing line. The ship turned off the line it was mapping and circled around until it was pointing perpendicular to the first line. It then mapped a swath that cut over the ridge and across the first line. We are particularly interested in the area where the two lines cross. By comparing the data from two different approaches over the same spot, we can get a much more accurate reading of the depth and of which features on the maps are real and which are artifacts.
Rough seas, however, complicated the effort to line up the ship and fish in the right position. I became aware of these problems as I lay in my bunk. At about 3:30 in the morning, my bed started shaking, Worse yet, a deafening grinding noise made falling back to sleep impossible. It took me a moment to assure myself that the ship was not falling apart. Instead the bow thrusters, which happened to be right outside my room, were working hard to keep the ship on course. The bow thrusters propel the ship by taking in water, then forcing it out through a grid. This grid can be rotated 360 degrees and push or pull the bow in any direction. In this case, they were being used to maintain the ship's heading.
There was a second complication. We were approaching the ridge from the north. The transponders that enable us to track the fish had landed on the south side. The top of the ridge blocked the signals traveling from the fish to the transponders. Therefore, the navigator had to guide the ship and the fish without the aid of the transponders.
Even when the ship got into the right position and started to map the cross line, there were complications. The rough seas bounced the ship up and down. The movement of the ship was transferred down the cable to the fish. As you remember, every time the cable pulls the fish up or down, the quality of the sonar data deteriorate. The printouts of the sonar images become streaky and hard to interpret. Unfortunately, that was the case for this crossing line.
Still, this crossing line provided important information. The magnetometer on the fish worked perfectly, and we got good views of the summit of the ridge for data comparison.