Spectral Reflectance of Melting Snow in a
High Arctic Watershed on Svalbard:
Some Implications for Optical Satellite Remote Sensing Studies
Jan-Gunnar Winther1, Sebastian Gerland1, Jon Brre rbk2, Boris Ivanov3,
Alberto Blanco4, and Julia Boike5
Field campaigns were undertaken in MayJune of 1992 and 1997 in order to study spectral reflec-
tance characteristics of snow surfaces before and during melting. The investigations were performed
on snow-covered tundra at Ny-lesund on Svalbard located at about 79N. Spectral surface reflec-
tance (or albedo) was measured with two spectroradiometers covering wavelengths from 379 to
1110 and 350 to 2500 nm, respectively. Supporting measurements such as snow thickness, density,
content of liquid water, grain size and shape, stratification of snow pack as well as cloud observa-
tions and air temperature were monitored throughout the field campaigns.
Spectral measurements demonstrate that the near-infrared albedo is most affected by the ongoing
snow metamorphism while the albedo in the visible wavelength range is stronger affected by surface
pollution. Daily albedo measurements from 19811997 show that the albedo normally drops from
80% to bare ground levels (∼ 10%) in 2 to 3 weeks. The date when the tundra becomes snow-free
varies from early June to early July. The effect of cloud cover on surface albedo is illustrated by an
incident when the weather condition changed from clear sky to 100% overcast within 2 hours on
June 9, 1992, resulting in a 7% increase of the snow albedo (370900 nm). Additionally, the bi-
directional reflectance of snow was measured by taking spectral scans for viewing angles 0 (nadir),
15, 30, 45, and 60 for viewing directions facing the sun and at azimuths 90 and 180. The
increase in albedo relative to the nadir for all measurements is found to be 8, 15, 19, and 26% for
viewing angles 15, 30, 45, and 60, respectively. The largest anisotropy is seen for metamor-
phosed snow in measurements facing the sun.
Consequently, under such conditions it is necessary to correct for anisotropic properties of snow if
satellite-derived albedo is going to be considered as absolute values. Also, the large variability regis-
tered in surface albedo during melt-off is of importance when interpreting and calculating surface
albedo from satellite images as well as for energy balance modelling and for parameteri-zation of
albedo in climate models.
1 Norwegian Polar Institute, 9005 Troms, Norway
2 Norwegian Polar Institute, P.O. Box 5072, 0301 Oslo, Norway
3 Arctic and Antarctic Research Institute, Bering-38, 199397 St. Petersburg, Russia
4 Department of Geophysics, University of Helsinki, P.O. Box 4, 00014 Helsinki, Finland
5 Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, 14473 Potsdam,
Germany
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