Seven-Tenths Read Free Page A

the sea floor actually looks a ship using this method would have to make a laborious succession of very closely spaced passes. Otherwise, only a narrow cross-section of the seabed being traversed is possible.
    A way around this difficulty was pioneered at the Institute of Oceanographic Sciences in Surrey. Instead of using vertical echo sounding, they developed a sidescan sonar in which the sound pulses are emitted sideways in two slanting fans, one on either sideof the ship and at right angles to its course. The outer edges of these fans brush irregularities on the seabed as far away as 30 kilometres. The returning echoes, since they do not come merely from a single point directly beneath the vessel’s keel, are complex and take skill and experience to interpret. Yet the profile which emerges from the plotters provides by far the clearest imagery yet possible of a continuous swathe of seabed, certainly on a cost-effective scale. GLORIA’s efficiency is striking. In good conditions and with the ship travelling at 8 or more knots it can reveal a strip of seabed 60 kilometres wide. In twenty-four hours this amounts to mapping more than 20,000 km2, or an area the size of Wales.
    This cruise in the Farnella is one of a series at the end of a great project on the part of the US to map the 200-mile EEZ around all 19,924 km of its coastline. The EEZ of the continental US has already been mapped, including Alaska and the Aleutian Islands. Now Farnella is working away at the Hawaiian Chain. As the scientists aboard keep telling me, only the GLORIA system could have covered such an area, and even that has taken ten years.
    Such things are explained as the ship bounces and judders through seasonal Pacific rollers on her way to the survey area. On and off a tropic sun blazes the sea to a luminous indigo across which flying fish skip and glide. In the intermittent bursts of sunlight there is a stampede of scientists up on to the deck where they grill themselves on towels, redolent of coconut oil. December! Hawaii! Field trips sometimes throw in for free the costly ingredients of other people’s holidays. They are watched by two boobies clumsily slithering on the button atop the radar mast while a small albatross flies elegant, mournful rings around Farnella . On successive days of watching I never once saw it move its wings, only soar and tilt in any direction and at any speed into the headlong breeze while keeping pace with the ship. It looked as though it knew by heart a map of the ocean’s surface, a map no man will ever make.
    Time was spent checking the various instruments which were soon to be lowered into the sea and towed behind us. First of all GLORIA itself: a large yellow torpedo lined inside with banks of transponders precisely angled to give the correct fan-shaped pulse.It sits in a hydraulic cradle directly over the ship’s stern. From time to time technicians climb up to tighten a nut and pat it protectively. Even without its cable it is worth nearly half a million pounds. There is spare cable but only one GLORIA aboard. ‘We don’t even like to think about that,’ is the response to the obvious ‘What if?’
    Amidships, two little ‘fish’ like fat yellow bombs wait on wooden trestles. These are the 10 kilohertz and 3.5 kilohertz sonars. The first will act more or less like an old-fashioned depth sounder to give the distance to the seabed immediately beneath us. The second will send pulses up to 400 metres into the ocean floor to provide some idea of the underlying geology. It is explained that its readout, taken by itself, would be fairly meaningless since in physics, as elsewhere, one cannot get something for nothing and the deeper penetration gained by using a higher frequency is at the expense of detail and spread. But taken in conjunction with information coming from other instruments this data will be usefully corroborative.
    Over the starboard stern will go the air gun. This is a heavy pot of machined