necessary for its speed and relative heading. 



Results of power spectra of surface wave motion obtained on the global circum- 

 navigational cruise of the USS TRITON (SSRN-586)* indicate that such spectra can be 

 measured successfully at speeds of 6 knots. At 6 knots, the TRITON's speed was equal 

 to the phase speed of a 2-second wave. Thus, spectra given in terms of the frequency 

 of encounter could be transformed in terms of the frequency relative to fixed coordi- 

 nates . 



C. Analog Estimation of Power Spectra 



The digital method of estimating power spectra may not be practical if a large 

 number of recordings are to be analyzed. This being the case, the recommended pro- 

 cedure would be to record analog data on a multichannel tape recorder and compute 

 energy spectra by commercially available wave analyzers. This was the method used 

 to analyze ship- and fluid-motion data presented in this report (References 4 and 7). 

 Most of the analog spectra of submarine and fluid motions presented in this report were 

 computed at the David Taylor Model Basin. The Hydrographic Office has recently 

 acquired the electronic components required to estimate power spectra shown in the 

 block diagram of Figure 7. An example of an analog spectrum of submarine roll angle 

 estimated by the system at the Hydrographic Office is shown in Figure 8. 



The analysis procedure is as follows: The random process to be analyzed is recorded 

 aboard the submarine on magnetic tape at a tape speed of 1 7/8 inches per second. Each 

 one-half hour run recorded at this speed is played on a 14-channel Ampex playback unit 

 (Fig. 7) at 60 inches per second while being re-recorded on a 14-channel Precision 

 recorder. The random signals are re-recorded also on an 8-channel Sanborn recorder so 

 that the quality of the recordings can be inspected, and an indication of expected am- 

 plitudes of the random signals can be obtained. This results in a compression of 1/32 

 the original recorded tape length; the frequency components in the random signal are 

 all increased by a factor of 32. The compressed recording is formed into a continuous 

 loop and threaded into a special loop attachment. The Precision recorder is utilized 

 again to drive the loop attachment at a speed of 30 inches per second for an additional 

 frequency increase of 16 times and a total frequency increase of 32 x 16 = 512 times 

 the original frequencies. Thus, a frequency of 0.10 cycles per second appears on the 

 analyzer as a frequency of 51 .2 cycles per second. The reason for analyzing in this 

 frequency range is that beat frequency analyzers commonly used can easily accommodate 

 frequencies at higher ranges, but could not handle gravity wave frequencies (e.g. 0.03 

 to 0.30 cycles per second). 



U.S. HYDROGRAPHIC OFFICE. Oceanographic data report for the global circum- 

 navigational cruise of the USS TRITON (SSRN-586). 16 February to 10 May 1960, by 

 N. R„ Mabry (in press). 



16 



