NSWC/WOL TR 76-155 



was no systematic discrepancy in surface sut-off time not accountable 

 to variation in sound speed over the two ray paths. 



The computations of steps 1 and 2 assumed that the sound 

 speed did not vary with depth. R. S. Price of this center has 

 developed a high-speed computer program which takes into account the 

 sound speed variation with depth--but assumes that the gages are in 

 a straight line. For the computations done here, these two effects-- 

 curvature of the gage line and sound speed variation--are the same 

 order of magnitude. In these computations, errors of about 0.4 

 milliseconds are caused by variations in sound speed. These 

 correspond to gage position errors of about 2 feet. For our purposes 

 errors of this magnitude were acceptable, however, significantly 

 improved precision could be obtained by accounting for both gage line 

 curvature and sound speed variation in the calculations . 



As a final check on the computations we compared the 



absolute time of arrival of the direct Shockwave measured on the 



pressure gage records to that calculated for the Shockwave travelling 



between our computed charge and gage locations. To do this we 



calculated the time, At , between the electrical firing pulse 



meas ^ ^ 



and direct Shockwave arrival as follows 



At = At , + VEL. CORR. + FIRING DELAY (Dl) 



meas sound 



where 



At , = transit time for a sound wave 

 sound 



VEL. CORR. = correction to At , to account for detonation 



sound 



wave velocity inside the charge and Shockwave 

 velocity in the water 

 FIRING DELAY = dwell time between firing pulse and initiation 

 of charge 



D-3 



