accomplished manually this is referred to as a dead reckoning 

 track. The dead reckoning analog indicator does the computation 

 mechanically and the present position can be read from instrument 

 dials or determined by the position of a "bug" on a chart. In 

 order for either plot to be accurate, the ship's speed over the 

 ground and true reading must be precisely known. Neither DRT 

 or DRAI is sufficiently accurate for the oceanographic program. 



The "SINS", SHIPS INTERNAL NAVIGATION SYSTEM, is a 

 more precise dead reckoning method which establishes the navi- 

 gation coordinates through measurements made by its gyroscopes 

 and accelerometer s . SINS uses two accelerometer s, one oriented 

 north-south and the other east-west, to determine ship travel 

 over the earth. The effects of gravity accelerations and ships 

 roll and pitch are eliminated by use of three gyroscopes. By 

 integration, present latitude and longitude, velocity and heading 

 can be determined. SINS would be an ideal navigator if it could 

 maintain accuracy for indefinite periods of time. However, due 

 to imperfections in these inertial sensors, SINS develops errors 

 that increase with time. Therefore, the system must be periodi- 

 cally corrected by navigation data from independent sources. 

 This limitation, coupled with the cost, size, and conriplexity of 

 SINS, will probably preclude its widespread use in the Survey 

 Program. 



Now, let us consider the shore-based electronic systems. 

 There are a number of such systems in operational use today. 

 However, most are designed for short-range or limited accuracy. 

 Consequently, I will confine my comments to those systems having 

 potential to the National Oceanographic Program. 



Prior to the outbreak of World War II, a need for aji all- 

 weather, high-accuracy, long-range aid to navigation was evident, 

 since before that time the radio beacon system, with its limited 

 range and accuracy, was the only electronic aid to navigation. 

 LORAN, which is an abbreviation of LOng RAnge Navigation, 

 was developed to meet this wartime requirement. The system 

 has been used extensively by both surface and aircraft since that 

 time; to differentiate it from newer loran systems, this is now 

 called loran-A. 



LORAN-A is a radio navigation system in which the trans- 

 mitting stations operate in pairs to provide the navigator a line 

 of position. The operation of a loran system can be summarized 



101 



