Chap. 2] METHODS OF GEOPHYSICAL EXPLORATION 37 



on the medium. Position finding is the procedure of determining one's 

 location by distance measurements from two acoustic sources of known 

 coordinates or, as in radio-acoustic position finding, from one source 

 transmitting a simultaneous radio and acoustic impulse. Conversely, 

 soimd ranging is the location of a source of unknown position by acoustic 

 triangulation, that is, by recording sound impulses on receivers of known 

 positions. By direction finding is meant the determination of the direc- 

 tion of sound by a rotatable base with two receivers (binaural hearing) 

 or with multiple receivers equipped with electrical delay networks to 

 balance their phase differences (compensators). Echo sounding is identi- 

 cal in principle with reflection shooting described on page 24, except that 

 because of the homogeneous character of the medium of propagation 

 (usually water) the devices may be so made as to indicate or record depth 

 directly. Noise prevention extends into the fields of architecture, building 

 construction, industrial activity, vehicle traJ0Sc, and sound insulation of 

 military conveyances. 



Military and peacetime applications of acoustic methods are numerous 

 and are covered in Chapters 6 and 12 in greater detail. 



