Marine MT System developed by Woods Hole Oceanographic Institution, USA Phoenix is co-operating with the world famous Woods Hole Oceanographic Institution (WHOI) to commercialize the state-of-the-art continental shelf MT (magnetotelluric) system developed by Woods Hole scientists.
The Atlantic continental shelf of the USA presents the worst conditions in the world for marine MT. But there, senior scientists at WHOI have successfully deployed their MT system. WHOI's system is specialized for continental shelf work, with a unique magnetometer design, tilt compensation and special filtering and data processing techniques.
Together with a land-based quiet remote reference station, this system will explore the
continental shelf wherever volcanic rocks, limestone, salt sills and other high-velocity layers impede seismic exploration.
Since the mid-1950s, MT has been used on land in thousands of oil and gas surveys worldwide to help image the subsurface geological structure in areas where the seismic technique cannot provide a clear picture. The same geological problems exist offshore but, until recently, there has been no suitable equipment for marine MT.
Acquiring seismic data at sea is usually easier and cheaper than gathering it on land, the opposite is true for MT.
There are many reasons for the increased difficulty and cost. The equipment must be sunk to the bottom in a controlled fashion and, once there, it must be self-levelling and self-starting. The equipment must be able to operate continuously for longer periods because the recording time required is longer than land based MT.
Low-power engineering is a must because, of course, there is no possibility of battery changes or solar-assisted batteries. The equipment must function perfectly in conditions of high pressure, while immersed in corrosive salt water and it must be properly anchored so strong currents can't sweep it away It must be able to measure the orientation of its own sensors and it must be retrievable on command. lust imagine sinking a $50,000 system in several hundred meters of salt water, then returning to the same location a week later, pressing a button to transmit an acoustic "release" signal, then, a few minutes later, seeing the costly equipment package bob to the surface.
Not only must environmental problems be overcome, the data processing and interpretation algorithms have to deal with noise sources radically different from those in land-based MT. For example, the sea water in which the equipment is immersed is conductive, and as the sea water moves through the earth's magnetic field, electric fields arise at right angles to the motion of the water and the magnetic field. Other noise arises from "internal waves" at the thermocline. and the steel hulls of passing ships create magnetic noise
Marine MT is new so there will be considerable growth in this area in the next few years as oil companies use a well-known tool (MT) to solve geological problems in a new environment--the continental shelf. We foresee a long and productive partnership with Woods Hole and its scientists.
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