48 OCEANOGRAPHY IN THE UNITED STATES 



Precision navigation, to be of surveying accuracy, requires a continuous 

 accurate knowledge of the vessel's position at all times while at sea. 

 It is this type of navigation which is employed by the Coast and Geo- 

 detic Survey for its hydrographic and oceanographic activities. 



Radio acoustic ranging (RAR) was developed in the 1920's for 

 accurately deteiTuining the position of the survey ship when out of 

 sight of land, day or night, in clear or foggy weather. Position of the 

 ship is determined by measuring the time for an explosive underwater 

 sound to travel from the survey ship to underwater hydrophones 

 placed at known locations. 



Since it was essential to have an accurate knowledge of the velocity 

 of propagation of the sound through the sea water, the survey vessel 

 took many samples of the water and measured the physical properties 

 to establish the sound velocity. These data have proven extremely 

 valuable to other oceanographic bureaus and to the Navy in the anti- 

 submarine warfare. 



Several important instrument developments came through the 

 Bureau's use of RAR, the most prominent being a sono radio buoy. 

 This is a portable station which eliminates the use of an expensive 

 vessel or ground station installation. The Navy patterned their sono 

 radio buoy after this design and made use of it for antisubmarine 

 warfare. 



Another important development was the discovery by Comdr. O. W. 

 Swainson and Dr. Carl Dyk of the phenomenon of long distance 

 sound transmission at deeper depths. Discovered in 1934 in the 

 course of oceanographic investigations concerned primarily with the 

 transmission of sound in sea water, this phenomenon was to have 

 important future application in the development of SOFAR, a long- 

 range signaling method over great distances at sea and used primarily 

 for location of ships in distress. 



RAR gave way to electronic positioning adapting World War II 

 developments such as shoran to our use in hydrographic positioning. 

 Due to shoran's approximate line of sight limitation, the Bureau de- 

 veloped its own electronic position indicator, which we call EPI, in 

 order to carry accurate positioning to greater distances offshore, up 

 to 500 miles and more. The Bureau is also using a coimnercially 

 developed navigational system and makes use of loran. 



In the field of tidal hydraulics notable achievements were made in 

 investigating forces and factors involved in the tidal regime. Early 

 discoveries and inventions form the basis of present day investiga- 

 tions in coastal geomorphology. 



Sigsbee, in his explorations almost 100 years ago, added materially 

 to our oceanographic knowledge, at the same time inventing and 

 developing many of the instruments and techniques for gathering and 

 measuring oceanographic data. The improved Sigsbee sounding ma- 

 chine added immeasurably to oceanographic investigations. Another 

 Sigsbee invention was a clam-bucket-type bottom sampler. The bot- 

 tom sampler is a device to obtain information on bottom materials 

 so that the bottom characteristics may be shown on the nautical chart. 

 Sigsbee also developed a multiple container that provided for simul- 

 taneous water temperature and water samples, with an automatic 

 registering device. 



