NSWC/WOL TR 76-155 



APPENDIX D 

 LOCATION OF FISH CAGES BY SOUND RANGING 



On four of the six shots of the 1975 tests, water currents 

 caused significant deviation of the charge and the fish cages from 

 their intended positions. The charge was suspended on one line and 

 the cages — with a pressure gage attached to each — where suspended on 

 another. In this appendix, we consider the problem of determining 

 the deviations of the charge and the string of fish cages from their 

 intended locations. 



The separation, x , of the two lines at the surface was 

 assumed known. Figure Dl shows the geometry of the problem. The 

 length of the charge support line and the lengths of line between 

 gages were also assumed known. We further assumed that the charge 

 and gages lie in the the same vertical plane. 



We solved this problem using the measured arrival times 

 of the direct Shockwave and its reflected tension wave from the 

 water surface at the respective gage locations. Step 1 was to use 

 the relative arrivals of the direct shock to determine an orientation 

 for the gage line giving a set of constant differences between the 

 calculated arrivals and the measured ones. Step 2 was to use these 

 gage positions to calculate the surface cut-off time — the time 

 interval between arrival of the direct shock and its reflection-- 

 and to compare these values with the corresponding measured values. 

 If there existed a systematic discrepancy in surface cut-off times 

 not accountable to variations in the sound speed over the two ray 

 paths, we then adjusted the angle, 8 , of the charge support line 

 and redid steps 1 and 2. The calculations were redone until there 



D-l 



