Cryosat-2 altimetry of BC Coastal Mountain glaciers

Cryosat-2 altimetry, for the period July 2010 to January 2016, shows widespread melting of glaciers in the southern part of the British Columbia (BC) Coastal Mountain range in western Canada. The Interferometric Radar Altimeter on Cryosat-2 is in synthetic aperture mode in this area, recording elevations of suitably-sloping targets out to about 5 km cross-track from nadir and hence giving full coverage between tracks separated by 5 km. Average height change rates were computed for small, overlapping subregions covering the study area. Subregions at altitudes less than 1500 m showed rates clustered symmetrically about zero. These targets could be confirmed by visual inspection to be from rock, soil or vegetated targets. Above 2000 m, more than half the targets show a broader distribution, indicating reducing altitudes (melting) by up to 2 m.year(-1). This second distribution is from the surface of glaciers. Melt rates above 1500 m decrease with increasing altitude and are lower before the start of 2013 than in the 3 years afterwards. Absence of negative melt rates (i.e., growing glacier heights over the full study period) is especially striking. The results show the capability of Cryosat-2 to measure individual and average melt rates on a timescale of 2-3 years.