E-4 



lengths) . 



For Leg E-2A-79 at Baltimore Canyon we believe that 

 we accomplished a continuous near surface positioning with 

 a standard deviation of ±5 meters for approximately 8 5% 

 of the time while surveying and for more than 95% of the 

 time when actually towing or sampling on station. For Leg 

 E-2B-79, where we could only rely on the Loran-C satellite 

 calibration, the navigational precision degraded. For 

 illustration purposes, Figure E2 plots for Julian Day 139 

 the latitude and longitude differences between 14 simul- 

 taneous satellite and Loran-C fixes. For the entire Leg the 

 mean difference in latitude was 104 meters and in longitude 

 was 127 meters. The largest differences were experienced 

 around sunset and at sunrise, due to progational anomalies. 



Sled Navigation 



The on-bottom tracking of the towed camera sled is 

 determined relative to the surface vessel using a combination 

 of acoustic slant ranging and internal on-bottom dead- 

 reckoning. For this purpose the sled was outfitted with a 

 synchronous pinger and a self-recording digital depth, 

 heading and speed sensor package. Its magnetic heading was 

 converted to true heading using the current measured magnetic 

 deviation. A schematic diagram of the ship and camera sled 

 system is shown in Figure E3. The horizontal range from ship 

 to sled (Fig. e4) was calculated from the acoustic slant 

 range (corrected for seawater sound velocity) and the pressure 

 depth (corrected for temperature and salinity effects to 



