To lay a cable competently you must have a detailed survey of a corridor surrounding the intended route. In shallow water, you have relatively precise control over where the cable ends up, but the bottom can be very irregular, and the cable is likely to be buried into the seabed. So you want a narrow (1 kilometer wide) corridor with high resolution. In deeper water, you have less lateral control over the descending cable, but at the same time the phenomena you're looking at are bigger, so you want a survey corridor whose width is 2 to 3 times the ocean depth but with a coarser resolution. A resolution of 0.5 percent of the depth might be considered a minimum standard, though the FLAG survey has it down to 0.25 percent in most places. So, for example, in water 5,000 meters deep, which would be a somewhat typical value away from the continental shelf, the survey corridor would be 10 to 15 kilometers in width, and a good vertical resolution would be 12 meters.
The survey process is almost entirely digital. The data is collected by a survey ship carrying a sonar rig that fires 81 beams spreading down and out from the hull in a fan pattern. At a depth of 5,000 meters, the result, approximately speaking, is to divide the 10-kilometer-wide corridor into grid squares 120 meters wide and 175 meters long and get the depth of each one to a precision of some 12 meters.
The raw data goes to an onboard SPARCstation that performs data assessment in real time as a sort of quality assurance check, then streams the numbers onto DAT cassettes. The survey team is keeping an eye on the results, watching for any formations through which cable cannot be run. These are found more frequently in the Indian than in the Atlantic Ocean, mostly because the Atlantic has been charted more thoroughly.
Steep slopes are out. A cable that traverses a steep slope will always want to slide down it sideways, secretly rendering every nautical chart in the world obsolete while imposing unknown stresses on the cable. This and other constraints may throw an impassable barrier across the proposed route of the cable. When this happens, the survey ship has to backtrack, move sideways, and survey other corridors parallel and adjacent to the first one, gradually building a map of a broader area, until a way around the obstruction is found. The proposed route is redrafted, and the survey ship proceeds.
The result is a shitload of DAT tapes and a good deal of other data as well. For example, in water less than 1,200 meters deep, they also use sidescan sonar to generate analog pictures of the bottom - these look something like black-and-white photographs taken with a point light source, with the exception that shadows are white instead of black. It is possible to scan the same area from several different directions and then digitally combine the images to make something that looks just like a photo. This may provide crucial information that would never show up on the survey - for example, a dense pattern of anchor scars indicates that this is not a good place to lay a cable. The survey ship can also drop a flowmeter that will provide information about currents in the ocean.
The result of all this, in the case of the FLAG survey, was about a billion data points for the bathymetric survey alone, plus a mass of sidescan sonar plots and other documentation. The tapes and the plots filled a room about 5 meters square all the way to the ceiling. The quantity of data involved was so vast that to manage it on paper, while it might have been theoretically possible given unlimited resources, was practically impossible given that FLAG is run by mortals and actually has to make money. FLAG is truly an undertaking of the digital age in that it simply couldn't have been accomplished without the use of computers to manage the data.Evans's mission was to present FLAG with a final survey report. If he had done it the old-fashioned way, the report would have occupied some 52 linear feet of shelf space, plus several hefty cabinets full of charts, and the inefficiency of dealing with so much paper would have made it nearly impossible for FLAG's decision makers }to grasp everything.
Instead, Evans bought FLAG a PC and a plotter. During the summer of 1994, while the survey data was still being gathered, he had some developers write browsing software. Keeping in mind that FLAG's investors were mostly high-finance types with little technical or nautical background, they gave the browser a familiar, easy-to-use graphical user interface. The billion data points and the sidescan sonar imagery were boiled down into a form that would fit onto 5 CD-ROMs, and in that form the final report was presented to FLAG at the end of 1994. When FLAG's decision makers wanted to check out a particular part of the route, they could zoom in on it by clicking on a map, picking a small square of ocean, and blowing it up to reveal sev-eral different kinds of plots: a topographic map of the seafloor, information abstracted from the sidescan sonar images, a depth profile along the route, and another profile showing the consistency of the bot-tom - whether muck, gravel, sand, or hard rock. All of these could be plotted out on meterwide sheets of paper that provided a much higher-resolution view than is afforded by the computer screen.
This represents a noteworthy virtuous circle - a self-amplifying trend. The development of graphical user interfaces has led to rapid growth in personal computer use over the last decade, and the coupling of that technology with the Internet has caused explosive growth in the use of the World Wide Web, generating enormous demand for bandwidth. That (in combination, of course, with other demands) creates a demand for submarine cables much longer and more ambitious than ever before, which gets investors excited - but the resulting project is so complex that the only way they can wrap their minds around it and make intelligent decisions is by using a computer with a graphical user interface.
Hacking wires
As you may have figured out by this point, submarine cables are an incredible pain in the ass to build, install, and operate. Hooking stuff up to the ends of them is easy by comparison. So it has always been the case that cables get laid first and then people begin trying to think of new ways to use them. Once a cable is in place, it tends to be treated not as a technological artifact but almost as if it were some naturally occurring mineral formation that might be exploited in any number of different ways.
This was true from the beginning. The telegraphy equipment of 1857 didn't work when it was hooked up to the first transatlantic cable. Kelvin had to invent the mirror galvanometer, and later the siphon recorder, to make use of it. Needless to say, there were many other Victorian hackers trying to patent inventions that would enable more money to be extracted from cables. One of these was a Scottish-Canadian-American elocutionist named Alexander Graham Bell, who worked out of a laboratory in Boston.
Bell was one of a few researchers pursuing a hack based on the phenomenon of resonance. If you open the lid of a grand piano, step on the sustain pedal, and sing a note into it, such as a middle C, the strings for the piano's C keys will vibrate sympathetically, while the D strings will remain still. If you sing a D, the D strings vibrate and the C strings don't. Each string resonates only at the frequency to which it has been tuned and is deaf to other frequencies.
If you were to hum out a Morse code pattern of dots and dashes, all at middle C, a deaf observer watching the strings would notice a corresponding pattern of vibrations. If, at the same time, a second person was standing next to you humming an entirely different sequence of dots and dashes, but all on the musical tone of D, then a second deaf observer, watching the D strings, would be able to read that message, and so on for all the other tones on the scale. There would be no interference between the messages; each would come through as clearly as if it were the only message being sent. But anyone who wasn't deaf would hear a cacophony of noise as all the message senders sang in different rhythms, on different notes. If you took this to an extreme, built a special piano with strings tuned as close to each other as possible, and trained the message senders to hum Morse code as fast as possible, the sound would merge into an insane roar of white noise.