The method of measurement employed the use 

 of an optical rangefinder and a standard naviga- 

 tion sextant. While the distance of the ship from 

 the iceberg was being determined with the range- 

 finder, certain characteristic elevations of the berg, 

 above the waterline, were being measured with 

 the sextant. The results of these measurements 

 allowed trigonometric computation of certain 

 vertical dimensions which were used as caUbration 

 measurements for the round of photographs which 

 were subsequentlj" taken. Several elevation meas- 

 urements were made on the different parts of the 

 berg and the mean for each characteristic height 

 was used. With each photograph calibrated by 

 one or more ineasured elevations, other dimensions 

 of the berg could be picked off tlie various photo- 

 graphs. After each photograph was adjusted for 

 the correct angular aspect, the horizontal widths 

 were measured starting at the waterline and at 

 25-foot intervals to the top of the berg. Indenta- 

 tions, gaps, and other surface discontimuties were 

 also measured in relation to the centerline as 

 shown in figure llC. With these measurements, 

 along with a relatively constant distance from the 

 t)erg for each photograph, a topographic map of 

 tlie bergs configuration above the water was 

 constructed, as shown in figure 12C. Starting 

 with the waterline, levels at 25-foot intervals 

 were subsequently constructed. The picture 

 measurements provided the widths and distances 

 for the construction of guide points on a plan view 

 of tlie berg. Once the guide points were estab- 

 lished, some artistic work was required to connect 

 the points and fill in the measurement gaps using 

 the photographs for reference. For the accura- 

 cies involved, the distance from the berg for 

 pictures taken beyond 400 yards could be con- 

 sidered at infinity because it affected the angle of 

 the constructed tangent lines very little. 



Once the scaled mapping was completed, a 

 planimeter was used to compute the areas at each 

 level. These areas were then integrated over the 

 entire height and the total volume above the water 

 was obtained. 



Daily measurements were obtained in an effort 

 to observe the changes with time in order to 

 correlate the measured mass reductions with the 

 observed meteorological and oceanographic pa- 

 rameters. Due to the cold conditions existing 

 during tiie study period, and tiie apparent slight 

 deterioration, only two volumetric determinations 

 were made. The maps used in these determina- 

 tions are shown in figure 13(_\ Tlie amount of 



visual change in the berg is displayed in figure 14C 

 showing similar aspect photographs taken at an 

 interval of 10 days. 



Data Correlation 



Environmental conditions of the study berg 

 remained relatively constant during the study 

 period. Figures IC and 4C, the plots of air 

 temperature during part of the study period and 

 the surface water temperatures as measured by 

 the ship's hull probe, show a sUght warming 

 tendency of the water. The upper water layers, 

 less than 5 meters, indicate temperatures above 

 0° C during the last few days of the study, how- 

 ever, the Nansen cast information indicates that 

 the berg's basic environment was subzero water. 

 This indicated that little subsurface deterioration 

 took place which seems to be substantiated from 

 the size measurements. Looking at figure 14C, 

 calving did occur during the period of study and 

 probably accounted for most of the loss of mass 

 above the water. Little or no correlation with 

 deterioration is seen from the wave height and 

 wave direction observations. As was pointed out 

 in the previous sections, the sea state ^vill cause 

 oscillatory motions of the berg and will contribute 

 to the subsurface turbulence in the bergs vicinity, 

 thus circulating the water and hastening melting 

 in the warmer environments. Wind velocity and 

 direction during the study period are shown in 

 figure 2C. 



Calculations based on the topographic maps 

 constructed from the berg's measurements provide 

 the volume of the above-the-water portion of the 

 berg. The total mass of the iceberg may be 

 obtained using the iceberg's density and the total 

 volume determination. Smith (1931) has made 

 actual measurements of iceberg density. He show s 

 a figure of 0.8997 gm/cm' as a mean. Due to the 

 contained air, this density value will vary from 

 berg to berg and within different parts of the berg. 

 However the density variation will be within 

 relatively narrow limits and the figure 0.9 gm/cm' 

 will be sufficiently accurate in comparison to 

 the accuracy in size determination. Using 

 Archimedes flotation principle tlie mass of the 

 iceberg can be calculated as follows: 



Percent of ice below the water 



density of berg 

 density of sea water 

 Total berg volume 



volume a boxe tlie water 



percent of total volume above the water 



50 



