Elevation change estimates of the Barnes Ice Cap from combined CryoSat-2 altimetry measurements and high resolution stereo-photogrammetric DEM

Abstract:

Mass losses from glaciers and small ice caps in the Canadian Arctic have accelerated dramatically in the last decade due to warming. The Barnes Ice Cap, a remnant of the Laurentide Ice Sheet, contains the oldest ice in the Canadian Arctic, and has been particularly sensitive to changes in atmospheric temperature. Although relatively flat at the top, the ice cap is located along the Arctic Cordillera, dominated by alpine mountains with sharp peaks and ridges which limited the accuracy of measurements from past satellite radar altimeter missions.

The interferometric capabilities of the CryoSat-2 radar altimeter has improved our capacity to measure volume changes over steep topography, but still face potential limitations over irregular terrain and glaciated areas with high surface roughness, which in the Arctic has increased as a consequence of intensified surface melt. Over rough topography, such as the one characterized by crevassed fields, surface roughness is high relative to the altimeter footprint, and estimating the incidence angle of the altimeter signal is not always possible. Here, a high-resolution stereo-photogrammetric DEM generated from stereo-mode Worldview satellite imagery is used to estimate surface slope of the glaciated terrain and derive the across-track incidence angle of the CryoSat-2 radar echo. The unprecedented accuracy of the DEM allows it to then be used as a reference to increase spatial density of elevation change measurements. Elevation change estimates for the period of 2011-2015 show a thinning of 1.46 ± 0.21 yr-1 on average, more than twice the thinning rates estimated a decade ago. The methodology increase spatial coverage of repeated altimetry measurements, and may improve elevation retrieval from altimetry signals in glaciated areas subject to summer surface melt.