| Summary: | We constructed high-temporal resolution time series of terminus position for Helheim and Kangerdlugssuaq glaciers, two major outlet glaciers of the Greenland Ice Sheet. Both glaciers terminate at tidewater in deep fjords. Calving front positions for each glacier are derived from ~daily resolution satellite images collected by the MODIS (MODerate resolution Imaging Spectroradiometer) sensors onboard the Terra and Aqua satellites. We use the MOD02QKM product which has a 250 m spatial resolution and is constructed from MODIS bands 12 in the visible part of the spectrum. Usable images are available for cloud-free days during periods of solar illumination, corresponding to near-daily coverage between 1 May and 31 October each year, and ~weekly coverage for the remainder of the year. Each terminus position was manually digitized according to the procedure described by Moon and Joughin (2008; Journal of Geophysical Research-Earth Surface) in which the calving terminus closes a polygon bounded on the sides by parallel lines approximating the lateral margins, and at the upglacier end by an arbitrary line well inland of the minimum observed terminus position. Repeating this procedure for each image yields the change in terminus area with time. We divide the area change by polygon width at each terminus position to obtain a width-averaged linear distance of advance/retreat. Uncertainty is ~250 m. For more details, see Schild and Hamilton (2013, Journal of Glaciology).
|
|---|