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« A *bit* of a tour of the Johnson Sea Link | Main | Good old-fashioned home-grown oceanography! »

Taking mapping to a whole new level

When you set out to drive somewhere, or to sail a boat, you put a lot of faith in maps.  You trust that things are where the maps says they are and that there’s nothing where the map says there’s nothing.  Can you imagine the chaos if the map didn’t sync up with reality?  It’s relaitvely easy to make faithful maps for roads because, for the most part, they’re man made, and someone planned and engineered them, so they have good survey data.  But for oceanic charts, its a bit different.  Charts are made by sounding (measuring the depth to the bottom at a specific point) and then joining up all the points of the same depths into contour lines (isobaths).  But because you can’t usually see the bottom over which you sail, you really have to trust that whomever made the chart did a decent job of it.

In this overlain image of two charts, you can see how one (the black lines) does not match the other (coloured lines)

Bill Baxley noticed that some of the charts for the area of the Abrolhos shelf where we are working don’t even match up with each other very well.  That means someone is right and someone is wrong, so Bill - the Harbor Branch director of technical operations for this expedition - is using downtime in between sub dives to better map the bottom.  At night, while the science crew grabs some much-needed shut-eye, Bill and the ship’s crew sail back and forth across the shelf break, taking super accurate readings of the depth using sonar equipment and precisely geolocating the soundings by GPS.  From all these data, he has not only created a much more reliable map for use on future research trips to this area, he’s even able to use GIS software to render the bottom in three dimensions.  In the movie below, Bill animated his map so that you can quite literally see the north shelf break of the Abrolhos platform rotating before your eyes.  He’s even put two submersible tracks on there.  The deeper of the two in red is the one where the bottle was seen, and on which this photo and video post was based.  If this isn’t just about the coolest thing ever, I don’t know what is!

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