E-7 

 variable lifetimes from perhaps only a few hours on 

 current swept sandy surfaces to dozens of years on muddy 

 slopes isolated from active scour. We have a fairly high 

 level of confidence that our sled tracks can be relocated 

 and individual photo sites revisited in the future by 

 employing navigational capabilities of the same degree of 

 accuracy as those used here. Operations in the future would 

 be all the more feasible if the revisiting is made by a 

 manned submersible capable of recognizing key landmark 

 marks recorded on our films. 



Camera Sled Operation (see also Fig. 4 of Final Report) 



The camera-sled ("Cheep Tow") used in the BLM field 

 program was designed specifically to be towed in contact with 

 the bottom on rough terrains. It employs a welded aluminum 

 frame fitted with buoyant spheres so as to be both self- 

 righting and to have only about 20 kg of bearing weight 

 on the substrate. Its righting movement prevents it from 

 being tilted by more than about 15 from the horizontal 

 as long as there are no net lateral torques on the skis . 



To decouple the sled movement from the vertical motion 

 of the surface vessel, it is towed behind a 500 kg depressor 

 on a 100 meter tether of neutrally buoyant polypropylene 

 line. Swivels are mounted both where the line attaches to 

 the sled and also at the depressor. The depressor is towed 

 with a 1/2" diameter steel cable from the ship's trawl 

 winch. The two cable passes through an accumulator to 



