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Multi-year evaluation of airborne geodetic surveys to estimate seasonal mass balance, Columbia and Rocky Mountains, Canada

Abstract. Seasonal measurements of glacier mass balance provide
insight into the relation between climate forcing and glacier change. To
evaluate the feasibility of using remotely sensed methods to assess seasonal
balance, we completed tandem airborne laser scanning (ALS) surveys and
field-based glaciological measurements over a 4-year period for six
alpine glaciers that lie in the Columbia and Rocky Mountains, near the
headwaters of the Columbia River, British Columbia, Canada. We calculated
annual geodetic balance using coregistered late summer digital elevation
models (DEMs) and distributed estimates of density based on surface
classification of ice, snow, and firn surfaces. Winter balance was derived
using coregistered late summer and spring DEMs, as well as density measurements
from regional snow survey observations and our glaciological measurements.
Geodetic summer balance was calculated as the difference between winter and
annual balance. Winter mass balance from our glaciological observations
averaged 1.95±0.09 m w.e. (meter water equivalent), 4 % larger than those derived from
geodetic surveys. Average glaciological summer and annual balance were 3 %
smaller and 3 % larger, respectively, than our geodetic estimates. We find
that distributing snow, firn, and ice density based on surface classification
has a greater influence on geodetic annual mass change than the density
values themselves. Our results demonstrate that accurate assessments of
seasonal mass change can be produced using ALS over a series of glaciers
spanning several mountain ranges. Such agreement over multiple seasons,
years, and glaciers demonstrates the ability of high-resolution geodetic
methods to increase the number of glaciers where seasonal mass balance can
be reliably estimated.
