APPENDIX C 



ICEBERG MOVEMENT 

 DETERMINED BY SATEL- 

 LITE 

 TRACKED PLATFORMS 



By 



D. L. MURPHY 



and 

 G. F. WRIGHT 



Introduction 



The International Ice Patrol (IIP) 

 deployed four satellite-tracked plat- 

 forms on icebergs drifting east of 

 Newfoundland and Labrador, 

 Canada during the 1989 iceberg 

 season. Two were deployed on 

 icebergs located in sea ice east of 

 Newfoundland in March as part of 

 Ice Patrol's participation in the 1 989 

 Labrador Ice Margin Experiment 

 (LIMEX '89). Two were also de- 

 ployed on icebergs floating in open 

 water east of Hamilton Inlet in La- 

 brador in mid-June. 



The satellite-tracked platforms were 

 TIROS Arctic Drifters (TADs), 

 manufactured by Polar Research 

 Laboratory of Carpenteria, Califor- 

 nia. They were tracked using the 

 ARGOS Data Collection and Loca- 

 tion System carried on two NOAA 

 satellites of the Tl ROS family, which 

 are polar orbiters. The system posi- 

 tion accuracy is about 350m. Typi- 

 cally, 6-10 fixes per day were re- 

 ceived for each TAD. The number 

 of fixes per day is directly propor- 

 tional to the latitude, so the TADs 

 depbyedfarthertothe north typically 

 provide more positions each day. 



The TADs, which were powered by 

 lithium batteries, were designed to 

 withstand the cold temperatures of 

 the high arctic. However, because 



the TADs were deployed at a rela- 

 tively low latitude (south of 55°N) 

 and in late winter and spring, alka- 

 line batteries also would have been 

 satisfactory. The TADs were sealed 

 to prevent water damage to the 

 electronics, and as a result they 

 floated. Therefore, they could con- 

 tinue to transmit even after falling oft 

 an iceberg. As a result, additional 

 effort is required to ensure that the 

 drift data represent iceberg move- 

 ment and not a TAD floating in the 

 ocean, but even with the best efforts, 

 this leads to much uncertainty. This 

 issue is discussed in detail later. 



All four TADs were deployed from a 

 ship-based helicopter. The TADs 

 were fitted with slings to lower them 

 onto the icebergs from the helicop- 

 ter. Theywere also fitted with pointed 

 steel legs to reduce sliding once 

 they were on the icebergs. Figure 1 

 shows the configuration of TAD 

 2612. Theotherthree were essen- 

 tially the same, although there were 

 some minor differences in the 

 physical dimensions. The approxi- 

 mate weight of each TAD was 25 kg. 



Data Processing 



The position data were fitted to a 

 cubic spline cun/e to obtain a record 

 with evenly-spaced intervals of 3 

 hours. The interpolated position 

 records were then filtered using a 

 low-pass cosine filter with a cut-oft 

 of 1.16 X 10^ Hz (about one cycle 

 per day). This filtering removed 

 most tidal and inertia! effects. From 

 the filtered position data, speed and 

 direction were calculated using a 

 simple backward-differencing 

 scheme. 



The following sections describe the 

 two deployments and present the 

 iceberg tracks. For convience, the 

 dates listed in this report are accom- 



panied in parenthesis by the year 

 dates, the sequential date numbers 

 starting with 1 on 1 January. 



L IM EX 

 TAD Deployments 



The two LIMEX TADs (4500 and 

 2612) were deployed as part of a 

 pilot experiment to examine difter- 

 ential iceberg/sea ice movement 

 during earty spring conditions. The 

 iceberg drift data were collected in 

 the context of LIMEX, a large, 

 multidisciplinary, international ex- 

 periment designed to invest igate the 

 physical properties and dynamics of 

 sea ice near the Labrador ice mar- 

 gin in the early spring. Other LIMEX 

 investigators collected data such as 

 sea ice distribution and movement 

 that will support the analysis of the 

 iceberg drift data. As these data are 

 not yet available, so only the iceberg 

 tracks are presented here. 



The strategy was to deploy the 

 TADs on apparently stable icebergs 

 (medium to large) far enough off- 

 shore to minimize the possibility of 

 grounding. They were deployed 

 using a twin-engine Messerschmitt 

 helicopter, which was based on the 

 CCGC SIR JOHN FRANKLIN. On 

 1 1 March (70), one TAD was placed 

 on each of two medium icebergs, 

 which were approximately 20 and 

 40 km, respectively, northeast of the 

 CCGC SIR JOHN FRANKLIN. 



In tx)th cases, the TAD was attached 

 to a hook on the underside of the 

 helicopter by a short length of line. 

 After arriving at the iceberg, the he- 

 licopter hovered 5- 1 m above it and 

 lowered the TAD to the surface. The 

 helicopter then circled the iceberg 

 so that the ice observers could pho- 

 tograph it and estimate its size. The 

 maximum height of the iceberg 



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