iceberg. Although the index of correlation (rho) is 0.81, the standard 

 deviation is ±5,600 yds. A poor deviation is to be expected considering 

 the diversified sources of information and the fact that the geometric 

 shape and therefore target gain of icebergs changes considerably from 

 target to target. Furthermore, from considerations to be presented later, 

 the value of the constant 3.78Xl0 1:i may change considerably with the 

 dielectric constant of the ice surface. In this respect it is important to 

 note that 80 percent of the observations were made on icebergs which 

 were in or approaching the shipping lanes. As will be seen later, the air 

 temperature near a floating ice formation materially effects the range of 

 detection; and the constant, K, should decrease with a decrease in tem- 

 perature, and therefore with an increase in latitude. In figure 24 the Ice 

 Patrol vessels' controlled observations are distinguished by solid circles. 

 The radar overall performance during these maximum range observations 

 was measured and found to be practically the same for all cases. 



Theoretical Detection Range of Growlers 



Based on equation ( 1 ) we can determine the magnitude of the maximum 

 detection range for the most dangerous of all ice formations, growlers. 

 Dangerous growlers from the exposed size of 10 sq. feet to 100 sq. feet 

 (usually about 10 feet high and approximately 250 tons) can be detected 

 at approximately 2 and 4 miles, respectively. Immediately, the danger 

 to a fast moving vessel becomes apparent. The possibility that the curve 

 presented in figure 24 might flatten out for the lower cross sections was 

 precluded by examination of 26 growler observations made by Hudson 

 Bay shipping [4] and 18 growler observations by the icebreaker Norlh- 

 ivind. These indicate that the expected range is even lower than that 

 presented here. 



REFLECTIVITY OF ICEBERGS 

 Reflected Power Measurements 



The behavior of ice as a reflector can best be measured by either labora- 

 tory or field observations of the quantity of power returned from an ice- 

 berg. As laboratory procedures obviate evaluation of the many parameters 

 of reflection interference, iceberg shape, propagation, etc., it was decided 

 to make the quantitative study of iceberg reflection on actual targets in 

 the vicinity of the shipping lanes or similar environs where possible. The 

 method devised in 1945, mentioned earlier, was used with few modifica- 

 tions. The echo signal strengths from the maximum range of detection 

 to the upper limit of the test set were measured on 26 approaches to 

 targets of various sizes and shapes. A typical run is illustrated in figure 

 25. On this large target (165 by 380 feet) duplicate runs were made to 

 determine the precision of the observation technique. These two series of 

 observations, indicated by open and solid circles on figure 25, show close 

 agreement and similar results were observed on another duplicate set. 

 The ordinate is the power received in decibels above minimum discernible 



57 



