Cartographie floue : le fond de l’Océan Indien
BBC News - Malaysia Airlines MH370: Searching in an ocean of uncertainty
The map is about 1,750km across. Ocean Shield’s detections have been made at about 20 degrees South
Look at the map at the top of this page. It shows the topography of the Indian Ocean bottom, west of Australia.
The star marks the rough location where the search vessel ADV Ocean Shield has been working this week, making encouraging pinger detections that could be the black boxes of MH370.
It’s on the northern edge of a small oceanic plateau, sometimes called Wallaby Plateau or Zenith Plateau.
But look again at the map, at the black lines that criss-cross back and forth.
The thick bands indicate tracks surveyed by modern acoustic echosounders, which map a swath of area along the path of the ship, and these are very accurate (to about 2%).
The thin tracks indicate older, low-tech echosoundings, which are not as reliable. They are, though, “direct” measurements.
That cannot be said for everything else you see. This is mapping conducted by satellites that infer the shape of the ocean bottom from the shape of the water surface above.
This kind of fuzzy mapping is pursued by satellites fitted with radar altimeters. Most of our maps of the gross outlines of mountains on the seafloor were produced this way - thanks to a 1985-86 US Navy satellite campaign and a 1994-95 European Space Agency effort.
Fuzzy mapping is a good phrase. The best resolution is about 20km. It’s thought there are somewhere between 50,000 and 100,000 seamounts that rise a kilometre or more above the seafloor, but which are invisible in these kinds of maps.