mapping the deep 10 Above: An illustration depicting how a submersible like the Limiting Factor can obtain seafloor data using portable sidescan sonar. Below: How that data might be represented in two-dimensional form. Multibeam sonar systems, such as the one attached to the bottom of the Pressure Drop, are effective for capturing the bathymetry (depth data) of large swaths of the ocean floor. Portable sidescan sonar systems, on the other hand, are used to produce more detailed images of the seafloor. These sidescan devices are often deployed closer to the seafloor and can more accurately read differences in material and texture down below. They do this by measuring the intensity of the return signals, rather than merely the time it takes for the signals to bounce back, as multibeam sonar does. This capability makes sidescan particularly effective for purposes such as finding shipwrecks, determining the state of underwater infrastructure, or locating mineral deposits. But portable sidescan sonar has never been deployed deeper than 6,800 meters (22,309 feet); its circuitry generally doesn’t hold up well against the immense pressure of the deepest sea. Now, though, a Mauritius-based company called Deep Ocean Search has developed a sidescan sonar apparatus that is designed to withstand the pressure and work at full ocean depth. Victor and Dawn have arranged for this new device to be attached to the outer shell of the Limiting Factor. If it functions successfully in Challenger Deep, it will represent a game changer in the field of seafloor mapping. At about 10,450 meters (34,284 feet), still roughly half a kilometer above the floor of the trench, the moment of truth arrives. Cradling a laptop computer, Dawn powers up the sidescan for the first time. Much to her relief, the sonar’s signals are reading clearly.
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