The sound channel was observed to be bottom bounded due to the 

 shallow depths of the area. Surface duct development was usually 

 restricted to the upper 10 meters and was observed most frequently 

 in September. 



At anchor stations, Nansen casts were taken primarily to investigate 

 possible correlations between periodic sound velocity variations 

 and the mixed tides characteristic of the Channel Islands area. 



From the resulting data, the 24 to 28 hours allotted for these 

 anchor stations appeared to be insufficient. A minimum of about 

 48 hours is necessary for a study of this type. Despite this drawback 

 some definite trends were observed. 



Figure 12 shows sound velocity vari- 

 ations at 400 meters for September anchor 

 stations 1 and 2. The ordinate is exag- 

 gerated to illustrate more clearly the 

 sinusoidal form of the curves. Sound 

 velocities at 400 meters for the entire 

 day had a range of 1.6 and 1.7 m/sec 

 for stations 1 and 2, respectively. 

 Comparing data from stations 1 and 2 

 at a particular hour, an estimated max- 

 imum difference of 1.2 m/sec occurred 

 in the earlier part of the day. From 

 1400 to 2200 Zulu, the differences ob- 

 served did not exceed 0.4 m/sec. Thus, 

 the difference of values between the 

 two stations at any hour is less than 

 the range of values over the entire day 

 for either station. This small difference 

 of hourly sound velocities between the two 

 stations is interesting considering that 



the two stations are approximately 19 miles apart, that San Nicolas 

 Island lies between them, and that the stations were occupied on 

 different days with some observations taken at different times. 









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2 . Comparison of Nansen Cast and Ramsay Velocimeter Methods . 

 Figure 13 shows the 400-meter sound velocity profile constructed 

 from the Ramsay probe data at anchor station 1 in October. The 

 sinusoidal curve also is evident; however, sound velocities were 

 several meters per second greater than those derived from Nansen 

 cast data. Figure 14 presents a comparison of sound velocities at 

 50 and 400 meters by the two methods for the same station. Difference 

 in sound velocities, A V, was determined whenever a Nansen cast 

 and a sound velocimeter lowering were made simultaneously. The 

 average difference was slightly more than 3.4 m/sec. The curves, 

 and especially A V, show the Ramsay probe values to be consistently 

 higher than those derived from Nansen cast data. The most probable 

 reason for this difference is an error in the multiplier or the zero 



13 



