651 



FiCLRE 14. Example of a Submari\e Upward-Looking Sonar Record from September 1993 



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scientific value of these data it should be borne in mind that their 

 primary purpose has been to avoid obstacles (icebergs and deep 

 pressure ridge keels) and locate thin ice for surfacing. Moored 

 sonars have been placed entirely in the service of scientific 

 research, but they have been in operation only during the past 

 four years. 



Between 1957 and 1975, the submarine sonar data were re- 

 corded in an analog mode. Starting m 1976, a digital recording 

 system was added to the analog recorder on a number (but not 

 all) of the cruises. The advantage of the digital system, which 

 is referred to as DIPS (Digital Ice Profiling System), is that it 

 greatly facilitates analysis of the data after the cruise has been 

 completed. The reason that the analog system was retained was 

 that it provided the crew with realtime information on the 

 position of the bottom of the ice overhead. Figure 14 shows an 

 example of these analog recordings. 



There is a large inventory of analog data that has not been 

 reduced from the original paper strip chart format (Table 5) 

 Accompanying these data are the associated records of location, 

 lime, depth, etc. necessajy to process the data into a scientifically 

 useful series of ice keel depth data points at specified locations. 



Paper strip cliansfrom analog 

 recorders generated during an 

 under ice experiment show the 

 variations in ice keel deptlis in 

 the central Arctic region. Several 

 major ice keels extend about 

 ^0-40 feet below the svrface. 

 The horizontal scale is actually 

 time, but given the ship speed 

 from ship's logs it also 

 represents distance traveled 

 under the ice. In the case shown 

 the major horizontal division is 

 approximately 0. ^ nautical miles. 

 This example has been 

 declassified by the Naxy through 

 omitting certain details that 

 would be necessary for scientific 

 use. including some level of 

 detail in location and time. 



From detailed discussions with the Navy concerning these 

 data, we have concluded that the analog records could produce 

 mean ice draft that would be accurate to within = 0.5 m, a value 

 that would be similar to the results of the analysis of the DIPS 

 data. In addition, since both analog and DIPS daia exist on a 

 number of CRiises. a quite exact estimate can be obtained of any 

 systematic differences between these two data sets as used on 

 exactly the same ice. These analog results would therefore also 

 yield valuable information on keel depths and distributions. 



The current data holdings (including the DIPS dai.i) are from 

 shghtly more than 50 deployments comprising approximately 

 1.800 days under the ice and 380.000 nm of ice information 

 (Table 6). Almost all cruises up to and including ihe present 

 have analog records of the sonar information while onl> 20 

 cruises have DIPS data. 4 of which had major recording 

 problems and are not useful, and 12 of which have been pre- 

 processed. 



b. Accessibility 



Except for the five earliest cruises (e.g., the Nautilus cruises) all 

 of the Navy s raw ice keel sonar data remain classified because 

 the complete records necessarily contain submanne tracks 



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