On To Day 15Back To Day 13Day 14. Counting Craters

By Edwin Schiele

October 9, 1998. This ship is filled with computers of every size and shape. These computers contain software that processes the data, organizes information, and generates colorful maps of anything you can think of. Yet many of the most basic analysis techniques come down to one simple tool—the colored pencil.

Jen Mercer identifying features (L. Dolby)
Jennifer Mercer plots the location of cratered volcanoes and fissured terrain (L. Dolby)

Now that we have completed the final swath along the top of the ridge, it is time to take inventory of the volcanic features we are seeing on the sonar print-outs. Here is how it works. The DSL 120 (or fish) collects the sonar data and sends them up the cable into the control van. A computer immediately processes the data and the Raytheon thermal printer spits out a continuous picture of the ridge in real time. The Raytheon also records the time at various intervals along the printout. Anybody can then look at the printout and determine the exact time the fish passed over a specific volcanic feature on the ridge. The sonar print-out does not, however, tell you where on the ridge the volcanic feature is located.

Side-scan image overlain on bathymetry (D. Smith)
Shown in the bottom panel is a side-scan sonar image of a terrace - its shadow is on the right. On the top the same side-scan data are overlain on the colored bathymetric surface (D. Smith)

To find the location of the feature, the scientist relies on information that the watch leader provides. As the Raytheon is printing the picture of the swath, the watch leader is plotting the position of the fish on a bathymetric (contour) map every 15 minutes.

Here is where the colored pencils come in. A scientist scrolls through one of the sonar print-outs in search of an interesting volcanic feature. She or he notes the time that the fish passed over that feature, then finds the exact position of the fish at that time on the bathymetric map. The scientist then takes a colored pencil—yellow for craters, pink for fractured areas, and brown for fissures—and plots the feature on the bathymetric map.

Once the scientists have plotted all of the cones and fissures, they can search for patterns. Are the volcanic features clustered together? How do they compare to the features on the subaerial (above water) portions of Kilauea or on the Mid-Atlantic Ridge?

The scientists can also match the feature with the bathymetry. On the sonar images it is often difficult to tell whether a crater is located on top of a cone or whether it is on a flat surface. This distinction is important. The presence of a cone indicates that large amounts of lava erupted from that spot. By overlaying the bathymetry, the scientist can determine the true shape of the feature.

Finally, by plotting the location of particularly interesting features, the DSL group will know exactly where to lower ARGO II so that it can take photographs.

Ship Tracks October 7 through October 9

Ship Tracks Oct. 7-9

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