Saturday, February 21, 2009
It's true that many amazing discoveries have been made in Google Earth including a pristine forest in Mozambique that is home to previously unknown species and the remains of an Ancient Roman villa.How little we know, indeed. Is this Atlantis? The conspiracy doesn't interest me all that much. Instead, I'm struck by the impression: the stamp left by the "systematic" tracing, the residue of the surface-to-sea-floor method (a term others have smartly untangled it into meta-hodos or something like 'beyond ways', even 'ways beyond'; this etymological dig lingers with me). The deep blue grid of "bathymetric data" elicits questions: why don't we see these in the adjacent areas? What was it about this boat, this collection process, this translation from sound to image, that left behind the vivid trails?
In this case, however, what users are seeing is an artefact of the data collection process. Bathymetric (or sea floor terrain) data is often collected from boats using sonar to take measurements of the sea floor.
The lines reflect the path of the boat as it gathers the data. The fact that there are blank spots between each of these lines is a sign of how little we really know about the world's oceans.
Robert Sarmast elaborated on the image's trail-grid, noting:
The lines you're referring to are known as "ship-path artifacts" in the underwater mapping world. They merely show the path of the ship itself as it zig-zagged over a predetermined grid. Sonar devices cannot see directly underneath themselves. The lines you see are the number of turns that the ship had to make for the sonar to be able to collect data for the entire grid. I've checked with my associate who is a world-renowned geophysicist and he confirmed that it is artifact. Sorry, no Atlantis.
More provocations here: the grid's unevenness, its predetermination, the inability of the sonar devices to see (erm...hear) directly below. And yet, a telling illustration of method alongside method: seems to me a subtle allegory in the adjacency of ocean floor imagery with lines and without. Presumably, the surrounding ground was measured similarly. Why no lines?Posted by Derek Mueller at February 21, 2009 7:45 AM to Methods