APPENDIX A 



SIZE FREQUENCY DISTRIBUTION OF 

 GRAND BANKS ICEBERGS 



R. Q. ROBE 

 U.S. Coast Guard Research and Development Center 



Historically, iceberg counts have been made by 

 an IIP estimate of the total number of iceberg 

 and growlers along the eastern Canadian coast 

 and the Grand Banks. Of necessity, very little 

 attention was given to the accurate determination 

 of size. Tabular icebergs were categorized 

 (Murray, 1968) as large (height greater than 50 

 ft.; length greater than 700 ft.), medium (height 

 20-25 ft.; length 300-700 ft.) and small (height 

 to 20 ft.; length less than 300 ft.). All shapes 

 other than tabular were categorized as very large 

 (height greater than 255 ft.; length greater than 

 700 ft.), large (height 150-255 ft.; length 400- 

 700 ft), medium (height 50-150 ft.; length 200- 

 400 ft.), small (height less than 50 ft.; length 

 less than 200 ft.). Although the ice observers are 

 highly trained, their estimates are subjective. 

 They must rely only on a practiced eye to place 

 a berg in one of the above categories. This re- 

 quires that they estimate range to the berg and 

 then evaluate its relative size against a back- 

 ground of ice or water, neither of which offer 

 any known object for size comparison. This esti- 

 mation is conducted at various flight levels, sun 

 angles, and visibilities. As a result, size estima- 

 tions result in a poor quantitative size distribu- 

 tion and are not useful for a detailed study of 

 iceberg sizes. 



With the advent of remote sensing possibilities 

 for iceberg detection, a more quantitative distri- 

 bution for iceberg sizes is needed. In order for 

 such systems as SEAS AT and SLAE (Side- 

 Looking Airborne Kadar), witli their greater all 

 weather detection capability, to be used to full 

 advantage, information on the population they 

 are sampling must be available. 



During the 1976 IIP season a CA-14 aerial 

 mapping camera was placed aboard the Ice Pa- 

 trol aircraft for a period of 47 days. On these 



flights, a total of 104 icebergs and growlers were 

 photographed. Altitudes for the photographic 

 flights ranged from 1,000 ft. to 11,000 ft. The 

 area covered by the photographed icebergs was 

 between 44°N and 51 °N and 45°W and 51°W. 

 Icebergs were photographed on a not to interfere 

 basis with the aircraft's primary mission of ice- 

 berg reconnaissance. Therefore, the sample does 

 not represent the totality of icebergs in the area 

 covered. Growlers of less than 10m 2 were not 

 counted. 



The frequency of icebergs versus horizontal 

 cross-sectional area (Figure A-l) indicates a 

 very strong peak for the small sizes. Icebergs 

 less than 1,000m 2 (but greater than 10m 2 ) ac- 

 count for 53 of the 104 icebergs in the sample. 

 The frequency drops off rapidly as size increases. 

 Icebergs in the interval 1,000m 2 to 2,000m 2 in- 

 cluded only 12 icebergs and the range 2,000m 2 to 

 6,000m 2 22 icebergs. Only 17 of the 104 icebergs 

 were larger than 6,000m 2 . 



SEASAT-A which is due to be launched in 

 1978 will carry a SAR (Synthetic Aperature 

 Radar) with a resolution of approximately 25m. 

 This resolution should make it possible to dis- 

 tinguish icebergs with a horizontal cross-sectional 

 area of greater than 1,000m 2 from ships and 

 debris. In the present sample, slightly more than 

 50% of the icebergs and growlers are smaller 

 than the 1,000m 2 . 



Data collection will continue over the next sev- 

 eral years to build an accurate base of informa- 

 tion on iceberg sizes as a function of both season 

 and geographic area. 



REFERENCE 



Murray, J. E., The Drift, Deterioration and Distribution 

 of Icebergs in the North Atlantic Ocean (Ice Seminar: 

 A Conference Sponsored by the Petroleum Society of 

 CIM, Calgary, Alberta, May 1968.) 



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