EXPERIMENTAL PROCEDURES 



365 



Two types of runs were made. In one, illustrated 

 in Figure 2, the target strength was measured as a 

 function of the aspect of the submarine; the sub- 

 marine, usually at periscope depth, proceeded at 

 creeping speed while the Jasper circled it, trying to 

 maintain a nearly constant range. The other, shown 

 in Figure 3, comprised opening and closing runs, and 

 was used to measure the echo level as a function of 



/ 



/ 



Figure 2. Circling run. 



range to determine the transmission loss. Here, the 

 submarine proceeded on a straight course while the 

 Jasper followed a divergent course, bearing approxi- 

 mately 60 degrees from the submarine and opened 

 the range until contact was lost; then a closing run 

 was made on a collision course down to a range of 

 several hundred yards. During both opening and 

 closing runs, the speed and course of the Jasper and 

 the submarine were held so that the aspect which the 

 submarine presented remained constant. 



Since these runs were made, a new type of fre- 

 quency modulation .sonar has been set up at the 

 Sweetwater calibration station of UCDWR for meas- 

 uring the target strengths of small objects.' It is be- 

 lieved that measurements may be made more quickly 

 with this system than with the standard pinging 

 system, but no results are available at the present 

 time. 



21.2.2 New London 



At New London, tests were made by CUDWR 

 aboard the USS Sardonyx (PYcl2) which echo- 

 ranged in Long Island Sound on the USS S-48 

 (SS159), a 1,000-ton S-boat 267 ft long, first com- 

 missioned in 1922.'' The submarine followed a straight 

 course at a keel depth of 80 ft while the Sardonyx 

 circled around it in an arc to maintain an approxi- 

 mately constant range. 



A device was used automatically to range on 

 center bearings. The amplified echo intensity was 

 kept constant by manual control of the amplifier 

 gain as the echoes were observed on a cathode-ray 

 oscilloscope. Relative echo intensity was obtained by 



recording the amplifier gain settings and by referring 

 to a calibration curve for the system. The bearing, 

 cour.se, and range of both vessels, and the gain 

 settings were recorded about every half-minute. Be- 

 cause complete calibration and transmission data 

 were not available, absolute target strengths could 

 not be computed. Instead, echo intensity was calcu- 

 lated as a function of aspect in decibels relative to the 

 echo level at an arbitrary aspect and plotted for 

 ranges of 600, 1,000, and 1,200 yd. 



USS JASPER 



^ SUBMARINE 



Figure 3. Opening run. 



21.2.3 Woods Hole 



Target-strength measurements were also made by 

 WHOI observers aboard the USS SC665 just off Fort 

 Lauderdale, Florida.*' ' Navy QCU sonar gear was 

 employed, with pulses from 60 to 80 msec long sent 

 out alternately at 12 and 24 kc, at slightly different 

 signal lengths to facilitate separation of the 12-kc 

 data from the 24-kc data. Apparatus was used to 

 range on center bearing. 



A hydrophone nondirectional in the horizontal 

 plane was mounted above the conning tower of the 

 210-ft Italian submarine Vortice. Accessory recording 

 equipment was installed aboard the submarine in 

 order to measure the level of the received signals and 

 to determine the transmission lo.ss from the SC665 

 to the submarine. The submarine proceeded on a 

 straight course, while the SC665 circled the subma- 

 rine to investigate aspect dependence, and opened 

 and closed the range to investigate range dependence. 

 The submarine also traveled at different speeds and 

 different depths in order to ascertain possible varia- 

 tion of target strength with the speed and depth of 

 the submarine. 



