OCEANOGRAPHY AND THE MARINER 



propagation, we should now find it easier to comprehend the princi- 

 ples involved in the formation of sound channels which exist through- 

 out the oceans. These channels are formed by a layer of water 

 having a negative (decreasing with depth) sound velocity gradient 

 overlying an adjacent layer having a positive sound velocity gra- 

 dient. In these particular circumstances, sound waves are confined 

 within these channels by refraction. 



Discovery of the existence of such permanent sound channels in 

 the ocean and their ability to permit transmission of sound for great 

 distances led to the development of many methods of underwater 

 communications and navigational aids. SOFAR (Sound Fixing And 

 Ranging) was utilized during World War II for the purpose of loca- 

 ting survivors at sea. By means of triangulation, shore stations could 

 determine the approximate position of survivors by detecting sounds 

 of exploding preset depth bombs dropped into the vicinity of a 

 sound channel by the survivors. A variation of SOFAR, RAFOS 

 (SOFAR in reverse), later proved highly valuable for determining 

 approximate positions of vessels by use of a hydrophone lowered to 

 a sound channel to detect sound signals produced by known stations. 

 More recently, underwater methods of navigational aid have given 

 way to more accurate electromagnetic systems such as RAMARK 

 (RAdar MARK), RACON (RAdar beaCON), SHORAN (SHOrt 

 RAnge Navigation), HIRAN (High precision shoRAN), electronic 

 position indicator (EPI), DECA, and RAYDIST. Inertial naviga- 

 tion has been of considerable value in submarine navigation. 



Oceanography is likely to play an increasingly important part 

 in precise submarine navigation. The submarine navigator of the 

 future will have much use for charts depicting expected sonar 

 conditions based on thermal structure of the oceans, as well as charts 

 showing such fixed features as bottom topography, major ciirrents, 

 and magnetic and gravity anomalies. 



Shark impaled on SONAR dome 



GEOLOGY 



The greater percentage of geologic oceanography deals with the 

 study and analysis of nearshore and open ocean depths (bathymetry) 

 and sediment composition. Many other fields comprise the lot of the 

 ocean geologist and geographer, e.g., magnetics, gravity, seismism, 

 volcanism, and erosion. All involve long and costly investigation 

 programs, requiring numerous manhours, complex instrumentation, 

 ships, reinvestigation, and above all cooperation between the report- 

 ing mariners, investigators, and worldwide government and private 

 hydrographic and oceanographic offices and observatories. 



The study of bathymetry is properly the lot of the hydrographic 

 surveyors, nevertheless, geologic oceanographers do construct numer- 

 ous special bathymetric charts in conjanction with bottom sediment 

 charts. All bathymetric charts are bound to contain a number of 

 obsolete soundings; constant attempts are made to revise them and 

 add to their worth by systematic hydrographic surveying. 



Sudden shoaling also may be the result of volcanic action. In 

 1934, an area of discolored water with depth of 43 fathoms was 

 reported in the North Pacific. A volcano in this same area attained a 



height of 150 feet above the sea within ten days in February 1946. 

 Volcanic action usually occurs along the concave sides of the great 

 ocean deeps, especially in the Pacific Ocean. Merchant and Naval 

 vessels should report all depth aberrations immediately to proper 

 port authorities for inclusion in the Notices to Mariners and Radio 

 Navigational Warnings. 



Bathymetric charts have been made for most ocean areas, 

 however, information is very sparse in some of these. Usually only 

 a fraction of the total number of soundings obtained in a thorough 

 hydrographic survey are included in the final chart, though all are 

 used in its preparation. Sparse or unevenly distributed soundings 

 are indicative of an incomplete survey. 



In deep oceanic areas, soundings taken about every half hour 

 or five to eight miles are sufficient for hydrographic purposes except 

 over the more outstanding features such as peaks and pinnacles. 

 Any prominent bottom feature in the ocean which can be determined 

 by fathometer readings can become a valuable aid to navigation if 

 its location is accurately determined and plotted. Proposals have 

 been made for the use of these prominent features as underwater 

 beacons for surface ship and submarine navigation and as anchoring 

 ground for deep water oceanographic telemetering instruments. Both 

 of these proposals will possibly become realities. 



Importance of the geologic oceanographers work in bottom sedi- 

 ment and seismic studies can be seen in the development of harbor 

 and submarine natural resources. The construction engineer relies 

 heavily on geologic and geophysical surveys for determination of 

 bearing surfaces or bedrock depths for marine construction. The 

 petroleum engineer relies on sediment analysis and seismic soundings 

 to reveal the most probable oil-bearing strata and thus the area in 

 which marine drilling is most likely to be successful. Detailed 

 bathymetric and sediment charts can be used for selection of best 

 holding grounds and anchorages of vessels. 



Submarine earthquake activity affects the mariner in several 

 ways: (1) interference with sonar operations, (2) disturbance of 

 biological activity, and (3) formation of so called "tidal waves" 

 (tsunamis). Other causes of extraneous underwater sound or motion 

 of this nature are volcanic activity, heavy surf, strong winds, and 

 landslides. 



The study of magnetic anomalies, e.g., magnetic storms in rela- 

 tionship to radio communications and gravity surveys for the 

 improvement of navigational charts, properly fall into the category 

 of geophysics rather than geologic oceanography. However, these 

 subjects often require sufficient understanding by the oceanographer 

 for purposes of editing and incorporation in specially requested 

 studies. Prediction of penetrating ability and travel path of electro- 

 magnetic (including sonic) waves has not been too successfully 

 correlated with bottom sediment types. However, electrical con- 

 ductivity or its reciprocal, resistivity, measurements can be made 

 from the sea surface taking into account the varying conditions of 

 the stratified nearshore water, of which each layer has differing 

 temperature and salinity values, the saturated bottom sediments. 



Part of the large variety of marine life tal<en off the bottom 

 of the ocean by an underwater dredge 



