SMOOTHED TEMPERATURE STRUCTURES 



The simplification of the data by low-pass filtering assumes 

 that the vertical variations of the higher frequencies have con- 

 siderably lower amplitude than those of lower frequencies, and 

 therefore should have less effect on the refraction of underwater 

 sound. 



The low-pass filtering was accomplished by running weighted 

 averages of the depth of each isotherm over 2-minute intervals 

 using half- minute increments. The high-frequency cutoff of the 

 filter is tt radians per minute or 107T radians per nautical mile. 

 The band pass is to 0.5 cycle per minute. 



The depths of the frequency-smoothed isotherms were 

 replotted on an expanded horizontal scale, and 0.2°C isotherms 

 were added by linear interpolation between the whole-degree 

 isotherms . 



Figure 4 displays the smoothed, low-pass-filtered tem- 

 perature structure from Sample Area 8. The horizontal scale is 

 shown as time but may be interpreted as distance with 10 minutes 

 equivalent to 1 nautical mile at the normal towing speed of 6 knots . 

 The vertical scale is 60 times that of the horizontal. These scale 

 factors also hold for the smoothed structures of the other 16 

 sample areas, shown in Appendix A. 



Three isotherms, the 15°, 16°, and 17°C, converge to 

 form an area of relatively steep temperature gradients at about 

 200 feet. 



This will be designated Area A. The addition of 0.2°C 

 isotherms between 12 °C and 15 °C made the phase coherence of the 

 vertical variations more obvious. The 20° C isotherm comes to 

 the surface at about time 1236, and the temperature structure 

 between 12°C and 15°C diverges about this same time. Even in 

 a simplified form the temperature structure remains complex. 



14 



