Hydrographic Surveying 



The principal hydrographic operations were carried on in x\laskan 

 waters. A total of approximately 244,000 miles of sounding lines were 

 run covering an area of 154,000 square miles. Prior to World War II 

 Coast and Geodetic Survey vessels in Alaska had completed charting 

 a large percentage of the waters of south-eastern Alaska and had made 

 good progress in charting south-western Alaska. With the outbreak of 

 the war the waters in the vicinity of the Aleutian Islands became 

 strategically important, and the bulk of the hydrographic work was 

 concentrated there. 



Since the close of the war these surveys have been extended, and 

 hydrography has now been completed in an area extending 60 miles 

 on either side of the island chain from longitude 170° E. to the general 

 vicinity of Kiska Island. A comprehensive survey has been initiated 

 in the Bristol Bay area and along the Arctic coast of Alaska, where little 

 is known of the depths of water, the character of the ocean bottom, or 

 the behaviour of tides and currents. 



The programme of deep-sea sounding-lines across the Gulf of Alaska 

 by Coast and Geodetic Survey vessels while en route to and from their 

 west coast bases was interrupted during the war years. Work was 

 resumed in 1945, and has since been extended into the north Pacific 

 Ocean. This extensive project has added greatly to our oceanographic 

 knowledge of the area. Many unknown submarine features have been 

 discovered and more complete data obtained on known features, notably 

 the Aleutian Trench. In 1947 an uncharted seamount was found in 

 latitude 51° N., longitude 143° W., which rose to a depth of 460 fathoms 

 from surrounding depths of over 2,000 fathoms. 



Off the Pacific coast of the United States hydrographic operations 

 were practically suspended during the war years. Since 1939 approxi- 

 mately 33,000 miles of sounding-lines were run covering an area of 

 6,500 square miles. Hydrographic surveys were started in the Midway 

 Island area in 1941, but were abandoned after the attack on the 

 Hawaiian Islands. 



In the course of the hydrographic operations numerous observations 

 were made for the determination of temperature and salinity of sea- 

 water. In addition, magnetic stations were occupied and the data 

 obtained have contributed to the maintenance of isogonic charts of the 

 ocean areas. 



Several notable developments in hydrographic techniques made 

 during the past ten years wiU have significant effects on the collection 

 of oceanographic data in the Pacific and elsewhere. Graphic recording 

 fathometers were adopted by the Bureau in 1940 as standard equipment 

 for hydrographic survey parties. This equipment greatly expedited 

 operations in shoal waters. Greater accuracy in echo soundings are 

 being achieved by improvements in the time-measuring device and in 

 operational techniques. 



Shoran, a wartime electronic development for pin-point bombing, 

 has been adapted by the Coast and Geodetic Survey for locating a ship's 

 position in hydrographic surveying at distances of 50 to 75 miles from 

 shore. The first surveys using this method were made in the western 

 x\leutians in 1945, and has since been extended to other areas. Shoran 

 has completely replaced the former radio acoustic ranging method. 

 Another electronic method, known as the electronic position indicator, 



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