BUCK: ARCTIC ENVIRONMENTAL LF ACOUSTICS I^IEASUREMENTS , 

 MODELS AND PLANS 



it is seen that the loss using T3 as receiver averaged about 5 dB 

 greater than ARLIS 5 as receiver. We have only two possible explana- 

 tions for this behavior: The T3 hydrophone lost sensitivity in the 

 2 years after calibration (but the top figures depicting noise indi- 

 cate it did not) ; or reflection conditions due to the presence of 

 the 7x4 miles, 100-foot thick ice island are different from the 

 9- to 12-foot thick pack ice and caused the added loss (shots from 

 T3 were set off in the pack ice immediately adjacent to T3 while 

 the phone was in the center of T3) . 



The data third from the top are S/N relative to ARLIS 5 of the 

 ice island and the 1972 floe station near the center of the Gyre 

 (for the latter, ARLIS 5 transmission loss was used) . Gyre-center floe 

 ice is 8 to 9 dB better than Gyre-southwest-edge floe ice and 3 to 8 dB 

 better than the ice island. 



The data at the bottom of Figure 22 are S/N ratios for three different 

 hydrophones at T3 relative to the 200-foot phone at ARLIS 5. These three 

 are: a unit 200 feet from the top ice surface installed at the center of 

 T3, an identical one close to an edge of the island, and a third one 

 located 128 feet below the top ice surface at the center of the island. 

 Location has little effect, when averaged as these data are, but depth 

 starts to be important above 30 Hz. 



The next set of figures describes an Arctic deep water test planned 

 for 1975-1977. As previously mentioned. Central Arctic ambient noise 

 is caused predominantly by ice dynamics. There is a large-scale 

 experiment called AIDJEX (Arctic Ice Dynamics Joint Experiment) 

 scheduled for the period March 1975 to June 1975 to collect and then 

 analyze and model ice pack motion for the understanding and prediction 

 of ice dynamics. An ambient noise measurement project has recently 

 been included in AIDJEX which, if it all comes off according to plan. 



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