DEPTH SURVEY CARRIED OUT WITH THE SONIC 



DEPTH FINDER 



Work was continued during 1927 with that part of the scientific 

 program which related to surveying the bottom contour in the ice 

 regions whenever opportunity offered. The work really has two 

 principal objects, (1) to contribute more cartographical information 

 than is now on record of these little frequented regions, and (2) to 

 learn more regarding the currents through a more detailed knowledge 

 of the sea floor, because as we well know, the configuration of a sea 

 basin casts an important influence upon the moving masses in it. 



The sonic depth finder apparatus was operated this season by a 

 member of the Coast Guard, a chief petty officer, who received an 

 eight weeks' course of instruction at the Navy sound school, United 

 States Navy submarine base, New London, Conn. The apparatus 

 functioned quite satisfactorily throughout the entire patrol. 



The calculations of the time interval used in multiplication to 

 obtain the depth, were facilitated by a graphic means of division, 

 the curves being constructed of a scale sufficiently large to permit 

 interpolation to 2 in the third decimal place of the time factor. 

 The velocity of sound in the water column, at the particular spot, 

 was obtained by referring to the chart that was especially constructed 

 for this region last year (Bull. No. 15, fig. 9, p. 49), in which correc- 

 tions have been made for the influences arising because of pressure, 

 salinity, and temperature. The geographical positions of the sound- 

 ing were not accepted until they had been tested by several 

 astronomical sights, and frequently supplemented by radio compass 

 bearings from Cape Race. 



There was a total of 435 soundings recorded this year which 

 range from as shallow as 30 fathoms to as deep as 2,312 fathoms. 

 A report and record of the data has been submitted to both the 

 United States Hydrographic Office and the United States Coast and 

 Geodetic Survey, in order that revision may be made in the proper 

 charts. 



One of the most important advantages that has been gained from 

 the sonic apparatus by the patrol has been of a navigational nature. 

 The distribution of the ice, and consequently the activities of the 

 patrol, take place in general along the Atlantic faces of the Grand 

 Bank, a region notorious for its fogs. In consequence the patrol 

 vessels experience considerable difficulty in obtaining frequent and 

 accurate astronomical "fixes." The depth of water, rapidly and 

 easily taken by means of the sonic apparatus, however, quickly locates 

 our distance in or out with respect to the bottom grade, while a radio 

 bearing from the only station in the ice regions. Cape Race, fixes 



our position along the slope. 



(51) 



