E-6 

 between range circles. The adjustment required for the best 

 fit to each range circle is attributed to transient effects 

 of near-bottom currents causing the sled to record an appa- 

 rent velocity that equals sled velocity plus current velo- 

 city. The offset vector is graphed at each 15 or 30 minute 

 interval as a means to assess the local variation in bottom 

 current speed and direction. 



Cross-track uncertainty is judged to be about 5 times 

 larger than along-track uncertainty, since the sled tracks 

 within a 15° angle from the stern of the surface vessel. 

 Our calculations allow us to estimate the cross-track uncer- 

 tainty to be on the order of 3% of the water depth. Exact 

 checks are made when sled transects intersect previous tracks 

 at near right angles. As an example, during Camera Run #6 

 in Baltimore Canyon the acoustic navigation could be used 

 to predict the recrossing of a sled mark. Study of the 

 film revealed the marks to be within 2 frames of the pre- 

 dicted frame (a distance of 12 meters.) 



The important consideration is that all the navigation 

 has been accomplished in an absoluate geodetic reference 

 frame. Therefore, cross-track calibrations take into 

 consideration the total accuracy of the entire geodetic 

 calibration and not just a measure of the ship to sled 

 ranging. 



When the camera sled is in contact with soft substrates 

 ski imprints are made and, judging from experience with past 

 submersible dives, these tracks can be expected to have 



