(Latitude & longitude unknown)Cable & Wireless MarineChelmsford, England

[Note: I left my GPS receiver on a train in Bristol and had to do without it for a couple of weeks until Mr. Gallagher, station supervisor at Preston, Lancashire, miraculously found it and sent it back to me. Chelmsford is a half-hour train ride northeast of London.]

When last we saw our hypothetical cable-ship captain, sitting off of Songkhla with 2,525 kilometers of very expensive cable, we had put him in a difficult spot by asking the question of how he could ensure that his 25 kilometers of slack ended up in exactly the right place. Essentially the same question was raised a few years ago when FLAG approached Cable & Wireless Marine and said, in effect: "We are going to buy 28,000 kilometers of fancy cable from AT&T and KDD, and we would like to have it go from England to Spain to Italy to Egypt to Dubai to India to Thailand to Hong Kong to China to Korea to Japan. We would like to pay for as little slack as possible, because the cable is expensive. What little slack we do buy needs to go in exactly the right place, please. What should we do next?"

So it was that Captain Stuart Evans's telephone rang. At the time (September 1992), he was working for a company called Worldwide Ocean Surveying, but by the time we met him, that company had been bought out by Cable & Wireless Marine, of which he is now general manager - survey. Evans is a thoroughly pleasant middle-aged fellow, a former merchant marine captain, who seemed just a bit taken aback that anyone would care about the minute details of what he and his staff do for a living. A large part of being a hacker tourist is convincing people that you are really interested in the nitty-gritty and not just looking for a quick, painless sound bite or two; once this is accomplished, they always warm to the task, and Captain Evans was no exception.Evans's mission was to help FLAG select the most economical and secure route. The initial stages of the process are straightforward: choose the landing sites and then search existing data concerning the routes joining those sites. This is referred to as a desk search, with mild but unmistakable condescension. Evans and his staff came up with a proposed route, did the desk search, and sent it to FLAG for approval. When FLAG signed off on this, it was time to go out and perform the real survey. This process ran from January to September 1994.

Each country uses the same landing sites over and over again for each new cable, so you might think that the routes from, say, Porthcurno to Spain would be well known by now. In fact, every new cable passes over some virgin territory, so a survey is always necessary. Furthermore, the territory does not remain static. There are always new wrecks, mobile sand waves, changes in anchorage patterns, and other late-breaking news.

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.