653 



FiGVRE 16. Area Approved for Release of 

 Future Akciic Dm 



This figure shows the boundaries of the area approved by the Navy for 

 release of environmental data from future Arctic sttbmarine exercises. 



could hope to develop seasonal distributions of ice thickness 

 extending over maiiy years and coveting important sections of 

 the Arctic basin. 



The Navy's ice draft acoustic data could also prove valuable in 

 developing and assessing methods for estimating ice thickness 

 and especially , ice thickness distribution, by satellite and aircraft 

 remote sensing (f.g.,ERS-l and Radarsat). For example, many 

 synthetic aperture radar images exist over the Arctic region, 

 especially the Beaufort Sea. Efforts to use these images to 

 estimate sea ice thickness are hampered by the lack of calibrated 



surface measurements. The Navy's ice draft data could fill this 

 gap if the track along which the data were collected could be 

 located in the SAR image. Sufficiently precise techniques do 

 exist to locate both SAR image pixels and the submarine track. 

 However, since release of detailed track data may be difficult, 

 and since few such tracks will happen to fall within existing 

 SAR images, only a limited number of detailed submarine ice 

 draft acoustic data with detailed locations would be needed. 

 Use of these acoustic ice draft data would support the long-term 

 scientific goal of creating ice thickness maps of the Arctic 

 regions using both aircraft and satellite remote sensing. 



One product that it would be possible to extract in a 

 straightforward way from the ice draft acoustic data would be 

 the distribution of ice thickness An example of what one 

 "snapshot" distribution might look like is shown in Figure 17 

 taken from the Southern Beaufort Sea (using data unrelated to 

 the Navy's classified data discussed here). 



During the cold season (September to May), new ice forms 

 wherever existing ice cover splits and diverges. Subsequent 

 motion under the influence of winds and ocean currents causes 

 the ice to shear, converge, raft, and ridge. The result is an ice 

 thickness distribution such as the one shown. This thickness 

 distribution is an important indicator of mechanical forces and 

 of heat exchange between atmosphere and ocean. Only upward- 

 looking sonar is capable of obtaining this information efficiently 

 and with the necessary accuracy. 



Figure 17. Distribution of Ice Drafts in the Southern Beaufort Sea 



The small maximum at Om represents open water 

 and very new ice having a thickness of only a few 

 centimeters. The poorly defined maximum at ice 

 thicknesses near 1 meter represents ice that has 

 grown as a result of ice divergence during the 

 past 1-2 months. The largest peak, near 2 meters, 

 is first year ice that started growing during the 

 previous autumn The broad maximum near 3 

 meters represents the preponderant population 

 ofmultiyear ice. The tad of the distribution 

 toward large thicknesses (greater than 4 meters, 

 extending to 15 meters} represents mechanically 

 compressed ice such as ridges and rafts. 

 The line rising to nearly 100%, associated with 

 the scale at the right, gives the cumulative area. 

 Thus approximately 75% of the area measured 

 contains ice that is 4 meters thick or less, and 

 approximately 95% is less than 10 meters. 



