4. Ice Thickness Campaign
4.1 Calibration Transects Compiled by Cathleen Geiger
4.2.3 Helicopter EM-bird Surveys Steffan Hendriks & Torge Martin
Sea ice thickness within the inner buoy array was measured with the EM-Bird on two days: April, 5 (Figure 4.2.7) and April, 9 (Figure 4.2.8). The flight profile is characterized by three successive triangles with a side length of 10 km. The waypoints were calculated by buoy positions of the respective morning then using the current position of the ice camp to estimate the recent buoy positions at take-off time. On April, 9, the second flight, all buoys were spotted by the crew during the flight.
Figure 4.2.7 : Sea ice thickness map of the inner buoy array on April, 5
An example of how ice thickness has changed along the inner buoy array is displayed in Figure 4.2.9. Despite the fact that not exactly the same ice was profiled during the two flights the typical characteristics of the region, such as large leads and ridges, first and multi-year ice, known from the first flight were observed again in the second profile. This can also be seen from the mean and standard deviations given in Table 4.2.1 and the frequency distributions of ice thickness in Figure 4.2.10 (left).
The change of the ice thickness distribution is displayed in Figure 4.2.10. A bin width of 10 cm is chosen for both histograms. The differences in ice thickness between the two profiles amount to less than 2 % for all bins. This confirms that the calibration of the EM-Bird was stable during both flights. The comparison of
the histograms shows, that the amount of thin ice (< 1 m) has decreased while the amount of ice with a thickness of 1.7 to 2 m increased. The trend for even thicker ice is irregular and can be treated as unchanged.
During the campaign wintry conditions prevailed and sea ice growth was more likely than melting. However, freezing can only partly explain the changes of the sea ice thickness distribution along the inner buoy array within these four days covered by the EM-Bird measurements. There was also no significant change in the snow cover. However, a few days with stronger winds had an impact on the ice dynamics, which can be determined from the buoy positions. A more detailed analysis of the buoy drift is necessary to clarify whether the change within the thick first-year ice range can be related to ice advection into the area of the inner buoy array.
Figure 4.2.8 : Sea ice thickness map of inner buoy array on April, 9
Figure 4.2.9 : Sea ice profile (20km) measured twice with a separation of 4 days.
Mean [m] Median [m] Standard Dev. [m] Length [km]
April, 5 2.61 2.46 1.25 111.4
April, 9 2.59 2.40 1.23 112.0
Apr. 9th 2.59 2.40 1.23 112.0
Table 4.2.1 : Sea ice thickness parameters of flights in inner buoy array
Figure 1.2.10 : Sea ice thickness distribution and change for inner buoy array flights
4.3 70km Scale
Flight navigation for the helicopter and aircraft transects between the camp and buoys in the 70km array was calculated using buoy positions transferred to the camp at 7am daily. Helicopter borne EM-bird provided the most comprehensive survey of ice thickness at the 70km scale. Rene Forsberg collected laser profile tracks in the northern quadrant of the 70km array (see section 4.2.2).
4.3.1 Helicopter EM-bird Surveys Steffan Hendriks & Torge Martin
Like the inner buoy array, the outer buoy array has been covered twice during the campaign by the EM-Bird: on April, 4–5 (Figure 4.3.1) and on April 11–12 (Figure 4.3.2). Each side of such a triangle had a length of approximately 70 km, which made six flights necessary in total to map sea ice thickness at this scale.
During the flights on April, 4 and 5 network problems occurred, which caused the loss of a few kilometres of data. Nevertheless, the amount of the gathered data in total ensures the derivation of reliable ice thickness distributions.
Figure 4.3.1 : Sea ice thickness map of the outer buoy array on April, 4– April, 5
Figure 4.3.2: Sea ice thickness map of the outer buoy array on April, 11– April, 12
Again the drift of the ice camp has been used to forecast the buoy position at the time of the measurements. However, the length of the flight tracks and the linked temporal delay was the main reason why a buoy was only spotted on a few occasions.
Figure 4.3.3 : Sea ice thickness distribution and change for the outer buoy array
The time span between both surveys was larger than for the inner buoy array (6-8 days) and a much larger region was covered by the measurements. Therefore, the observed changes in the sea ice thickness distribution (Figure 4.3.4) are different to those observed for the inner buoy array. More open water and very thin ice (< 20 cm) was found during the later part of the campaign, which is in good agreement with the visual observations. The depletion of thick first-year ice (1.5 – 1.8 m) accompanied by a decrease in multi-year ice (2.0 – 2.5 m) is not observed for the inner buoy array, whereas the fraction of very thick deformed ice was very stable on both scales.
Mean [m] Median [m] Standard
Dev. [m] Open Water
Fraction [%] Length [km]*
April, 4 – April, 5 2.70 2.51 1.26 0.02 533.7 April, 11 – April, 12 2.59 2.43 1.42 0.40 613.3
Apr. 11th – Apr. 12th 2.59 2.43 1.42 0.40 613.3
Table 4.3.1 : Sea ice thickness parameters of flights along the outer buoy array
*The difference in profile lengths does not represent the relative change in buoy positions but shows the gaps of EM-Bird data in the first flights.