the spectrum of the unfiltered signal while Curves B and C are the resultant spectra of 

 first passing the signal through a Krohn-Hite Band-Pass Filter, Model 320A. Cut-off 

 limits were arbitrarily set at 0.08 to 0.5 cycles per second (periods of 2 to 12.5 

 seconds) for Curve B and 0.09 to 0.5 cycles per second (periods of 2 to 1 1 .1 seconds) 

 for Curve C. Filter response curves for the frequency band used to obtain Curve B 

 are shown in Figure B3. It should be noted that the shape of the filter response curve 

 allows a fraction of the energy associated with frequencies less than 0.08 cycles per 

 second to pass, but blocks off the very low frequencies. 



FIGURE Bio COMPRESSED RE-RECORDING OF IN SITU PRESSURE FLECIUATI01I3 



A digital spectral estimate of this same run was obtained by re-recording the 

 filtered run with pass-band limits set at 0.05 to 0.5 cycles per second. In Figure B4, 

 the dashed curve is the power spectrum of this filtered recording; the solid curve, 

 surface power spectrum; and the dashed-dot curve, the residual power spectrum at 60 

 feet obtained by attenuating the surface power spectrum according to: 



/A(/a)7 2 c = (e~^) /AW 

 *- -^60 feet \ L J *- Jf, s 



2 



Surface 



where Z and L are given in Appendix A. 



The difference between the in situ power spectrum and the residual spectrum at 

 60 feet due to surface wave motion alone is attributed to pressure fluctuations associ- 

 ated with the submarine motion; i.e. roll angle and cross-flow. 



58 



