The freeboards of iceberg A-68 were derived from the CryoSat-2 observations inside the boundary of the iceberg identified from the Sentinel-1 SAR images acquired on the same dates. The CryoSat-2 profiles acquired on different dates were relocated to the location on 8 September 2017 based on the drift speed and rotation angle of the iceberg. The freeboard changes were calculated at the intersections of the CryoSat-2 profiles.
CryoSat-2 profiles on iceberg A-68 overlaid on the Sentinel-1A SAR image on 8 September 2017.
Freeboard changes before January 2018 were positive (an averaging change of 0.82±0.38 m/year) which indicates the freeboard rising. CryoSat-2 uses the Ku-band that might measure the height at snow surface due to high densification of snow/firn layer. The snow depth in this region continued to increase, showing a change rate of 0.82±0.06 m/year. Therefore, the increase in the freeboard of iceberg A-68 was likely the result of increased snow depth on the ice surface, not ice thickening.
Freeboard changes after February 2018 were negative, with an averaging change of –0.80±0.29 m/year which is greater than the rate of snow depth increase. In other words, the thickness of A-68 has decreased dramatically since February 2018. This likely reflects warm seawater during the Antarctic summer, and an increase in the relative velocity of the iceberg resulting from drift in winter promoted the basal melting. Assuming that CryoSat-2 observations reflect the snow surface, the thickness change after February 2018 was –12.89±3.34 m/year.
Detailed analysis of freeboard change in iceberg A-68 can be found in the paper below.
Han, H.; Lee, S.; Kim, J.-I.; Kim, S.H.; Kim, H.-C. Changes in a Giant Iceberg Created from the Collapse of the Larsen C Ice Shelf, Antarctic Peninsula, Derived from Sentinel-1 and CryoSat-2 Data. Remote Sens. 2019, 11, 404.