BUCK: ARCTIC ENVIRONMENTAL LF ACOUSTICS MEASUREMENTS, 

 MODELS AND PLANS 



ocean noise and propagation. Shown on the top figure are the familiar 

 Wenz curves for deep water. Superimposed are the 5, 50, and 95 per- 

 centiles of hourly measurements taken over a 2-month period in the 

 spring from a floe station 150 miles north of Barrow, Alaska, on 

 the southwest edge of the Pacific Gyre. Note that 5 percent of the 

 time the noise is only 10 dB above Wenz ' s "lower limit," but another 

 5 percent of the time it is considerably higher than the open ocean 

 "usual deep water traffic" below 200 Hz and higher than a wind-force- 

 5 surface wave noise above 200 Hz. 



The bottom figure compares selected samples of open ocean trans- 

 mission loss data with Arctic deep water at 120 nautical miles. Only 

 below about 60 Hz is the loss in the Arctic comparable at this range. 

 At 400 Hz it is some 40 dB greater than Artemis data and 50 dB greater 

 than for the wintertime Mediterranean. 



The comparisons in Figure 3 are representative, only, since the 

 Arctic has been foimd to be highly variable, not only diurnally and 

 seasonally, but also geographically. For example, measurements have 

 indicated ambient noise levels (see Figure 4) at or near the center 

 of the Pacific Gyre (position "A") are 8 to 10 dB lower than Gyre 

 edge (positions 5 and 6) , and long-term measurements show that an 

 ice island, such as T3, is also much quieter. 



As one might expect for the RSR conditions of the Arctic, long- 

 range, low-frequency transmission loss is determined by bottomside 

 ice roughness, bottom depth and source and receiver depths. Low 

 frequency ambient noise in the central Arctic is almost totally 

 caused by ice dynamics — pressure ridging, cracking and grinding 

 of the moving ice. 



731 



