By switching between these beams upon request—a process known as demand assigned multiple access (DAMA)—multibeam satellites can link widely distributed mobile and fixed users that cannot be linked economically by optical fibre cables or earthbound radio relays.
High-frequency sound (12 kilohertz), radiated by the transducers of the Simrad EM 122 swath multibeam, bounces back from the seafloor surface.
As of midnight, the Langseth had collected more than 2,000 line kilometers of multichannel seismic reflection and other track data (multibeam swath, sub-bottom profiler, gravity and magnetic anomaly).
The multibeam also reveals pockmarks on the seafloor, circular depressions caused by the explosive discharge of gas from below the seabed, and fields of oriented grooves caused by the advance of glacial ice across parts of the Chukchi Borderland.
With the multibeam swath mapping system, the sediment surface below is revealed.
We have seem numerous ice gouges in the multibeam data.
We can monitor the ship's position, heading and speed; wind speed and direction; activity throughout the ship on the closed-circuit TV system; the firing status of each of the 10 air guns; the subbottom profiler; the multibeam; and the geometry of the hydrophone array, in depth and in map view, strung out behind us, extending six kilometers back toward where we've been.
There are three watch standers processing the multibeam bathymetry data, watching the various screens and making notes about the events of the watch.
The next phase starts with a bathymetric survey: a rough mapping of the hitherto uncharted ocean floor, from the surface using multibeam sonar.
The same multibeam data was used by the World Wildlife Fund and a Canadian oil company, Sable Offshore Energy, when establishing Canada's Sable Gully Marine Protected Area.
Under Article 76 of United Nations Convention on the Law of the Sea, which has not been ratified, multibeam data will be used to support Canada's -- and several other countries' -- claims of jurisdiction over their continental slopes beyond the currently recognized 200 miles.
