OCEANOGRAPHY 1961 — PHASE 3 213 



nients for speed, reliability, auf.oniatic operation, and refined methods of sensing 

 is now j?oing on at an accelerated rate. In order to build up the capability for 

 such developuient, the exploration industry had to estai»lish research labora- 

 tories and acquire highly trained scientists. This resulted in the ability to 

 attack all kinds of problems in instrumentation, oceanographic or otherwi.s<\ 

 so that now the industry has produced such items as bathythermographs, sonar 

 gear and magnetic submarine detection devices. 



Regular exploration instruments adapted by the industry for use at sea in- 

 clude principally magnetometers, gravity meters, acoustic arrays, or seismo- 

 graphs, and computing and data-processing gear. 



Gravity meters were first used in water by giving them remote reading devices 

 and lowering them to the bottom from ships that anchored for the purpose or 

 from hovering helicopters. It was found that if the bottom were muddy it 

 responded to swells with so much motion that the gravity meter had to be 

 modified so as to be readable while its frame was moving. This led to the in- 

 vention of devices to compensate for larger and larger motion, so that gravity 

 meters were adapted first to submarines and then to surface ships. At present, 

 gravity can be read in surface ships of moderate size, without stable platforms 

 and in average sea states, with an accuracy of two parts in a million. 



In a similar way magnetometers were adopted for seagoing use, except that 

 a new instrument had to be devised instead of merely modifying the reading^ 

 method of the old one. The flux-gate magnetometer was invented by the ex- 

 ploration Industry and adapted for use in airborne submarine detection in 

 World War II. It was operated by being towed in a "bird" behind an airplane. 

 Since the instrument could be read in spite of the motion of such a bird it could 

 be used without modification in the water by being towed behind a ship, and it 

 has been so used by geophysicists and by physical oceanographers since. Later 

 developments have included new types of magnetometers such as the proton- 

 precession, the rubidium-vapor, and the metastable helium magnetometers. The 

 last named is again being used in airborne submarine-detection systems. It has 

 the advantage of giving an absolute omnidirectional reading, and it is from 

 100 to 1,000 times as sensitive as the first airborne or water-towed magnetom- 

 eters. 



It is the adaptation of seismograph systems or acoustic arrays to ocean use 

 that the most satisfactory results have been achieved by the exloration industry. 

 Today's waterborne acoustical arrays, the result of 25 years' development, are 

 housed in a cable half a mile long containing 24 detectors. This is towed by a 

 ship traveling at 6 knots which pays out the cable from a reel while a dynamite 

 charge is fired and the signals from it are recorded, and reels the cable back 

 in automatically during the 2-minute intervals between shots. Thus a con- 

 tinuous-coverage map of the bottom and the subsurface geologic structure to a 

 depth of 3 or 4 miles below the bottom is made at the rate of 60 or 70 miles a 

 day. A recent development involves the use of a gas gun instead of dynamite; 

 the gun is cheaper than dynamite but does not have as much penetration. 



The success of the oceangoing seismometer, and the large quantities of data it 

 brought in, made it necessary to invent automatic data-processing systems for 

 correcting, computing, and plotting the data so as to eliminate the quantity of 

 liand computing and hand plotting previously needed. The processing of records 

 led to the Invention of a t3T)e of inverse-filter processing whereby a signal could 

 be lifted out of a noise level so high that the signal would have been imperceptible 

 on a visual record of the old type. 



In addition to the geophysical instruments now used by physical oceano- 

 graphers at sea, the exploration industry manufactures a number of instru- 

 ments that are specifically oceanographic. One example of this is the electric 

 bathythermograph. This is an instrument which can be lowered into the ocean 

 from a ship or a hovering helicopter and which records the temperature of the 

 water at different depths, an important item in antisubmarine warfare. Another 

 example is the application of the new accurate magnetometers to submarine 

 detection, whether towed from a ship or airplane or lowered from a helicopter. 

 A third example is the development and application of sonar gear. The problems 

 of sonar in the water are the same as the problems of sound in the earth : in 

 both technologies a deduction is made from hearing a noise that has traveled 

 through a dense medium, water in the case of sonar and rock in the case of oil 

 exploration. In each case the signal must be amplified, filtered, and displayed, 

 before the observer may make a deduction from it. If an array is available the 



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