Tim O’Hare
observations, thoughts and useful stuff…Archive for oceanography tools/data
Down down, deeper and down
There’s a report on the BBC website about a new robotic submarine that is currently undergoing final preparations ahead of an attempted dive to the deepest part of the world’s oceans, The Challenger Deep in the Mariana Trench (~11,000 metres down). This depth is deeper than Mount Everest is high (incidentally, did you know that George Everest’s name was actually pronounced Eve-Rest rather than the Ever-Est that we now use to describe the mountain that was named after him?). The robotic submarine has been developed by scientists and engineers at the Woods Hole Oceanographic Institution in the USA and is named Nereus (after the son of Pontus [the sea] and Gaia [the Earth] in Greek mythology). Challenger Deep has previously been visited only twice before, both times by human-operated vehicles, so there is plenty of potential for Nereus to turn up some interesting information. The Challenger Deep is part of a major subduction zone in the western Pacific in which oceanic crust that forms the base of the Pacific Ocean is forced down and underneath the oceanic crust that neighbours the Asian landmass and for this reason it is a major earthquake region. At this kind of depth the pressure experienced due to the weight of water supported is over 1000 times greater than the pressure we experience at sea level (due to the weight of the overlying air in the atmosphere).
Ocean Gliders
Way back when I was a PhD student one of the big fusses in oceanographic circles was an autonomous instrument platform that was under development called Autosub. Autosub is a fairly large autonomous submarine capable of powering its way through the oceans whilst carrying a payload of oceanographic instrumentation. Everyone was excited about the possibilities that Autosub would provide but it was some time before the plans came fully to fruition (the first science missions were carried out in 1998).
Without wishing to do anyone a dis-service, the story that I heard was that the original calculations of the weight of the required battery packs were wrong and so when the first attempts to build Autosub took place it was impossible to get the whole package to float… only when battery technology had advanced several steps was Autosub able to get back on track. I’ve no idea whether this story is true, but if it isn’t it should be because it is a much better excuse than simply saying that these things take time. Anyway, following six science mission campaigns funded by the Natural Environmental Research Council, Autosub moved onto its full-on wow-factor missions, Autosub-Under-Ice although an Autosub did become trapped beneath Antarctica on only its second mission under ice mission. There is a BBC Radio 4 “The Material World” programme on Autosub that was broadcast just before this incident.
More recently, there have been a number of other developments using autonomous underwater vehicles to measure oceanographic parameters. One such involves a trio of robot gliders that are being used to profile the top 1000m of the Atlantic Ocean between the Canary Islands and west Africa. The measurements are being made as part of the Rapid-WATCH programme (Rapid Climate Change – Will the Atlantic Thermohaline Circulation Halt?) and help to fill gaps in data coverage that resulted from traditional moorings being damaged by trawlers. The gliders, which are under 2m long use a pair of floatation bladders within which oil is pumped to vary the buoyancy and thus cause upward or downward movement of the glider. There are also now plans to use the gliders in the waters off Antarctica and also for a new generation of gliders, so it seems as though the early work, and the excitement this generated back in the late 1980s and early 1990s is finally paying off. There is a New Scientist article (Issue 2684, 29 November 2009) on the gliders being used within the Rapid-WATCH programme.
Google Oceans
Google Earth has been around a few years now and many people are familiar with it as a tool that “lets you fly anywhere on Earth to view satellite imagery, maps, terrain, 3D buildings, from galaxies in outer space to the canyons of the ocean. You can explore rich geographical content, save your toured places, and share with others” (Google Earth website). Now Google Earth has been upgraded to allow users to view large parts of the ocean floor. Given that oceans cover over 70% of the Earth’s surface, the existing Google Earth had to be upgraded at some point but the addition of ocean seafloor has meant a change from the satellite sensors used to provide mapping information for the land surface to the acoustic sensors that are used by marine surveyors to map the seafloor. Much of the seafloor data has come from the US Navy and this means that there are blank regions in sensitive areas. Google Oceans can be obtained by downloading (for free) the latest version of Google Earth. You can read more about this new facility on the BBC website and at New Scientist magazine.
