The Cryosphere Discussions
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2011
10.5194/tcd-5-2991-2011
http://www.the-cryosphere-discuss.net/5/2991/2011/
http://www.the-cryosphere-discuss.net/5/2991/2011/tcd-5-2991-2011.html
http://www.the-cryosphere-discuss.net/5/2991/2011/tcd-5-2991-2011.pdf
2991
3024
2011-10-27
Melt ponds on Arctic sea ice determined from MODIS satellite data using an artificial neural network
A. Rösel
anja.roesel@zmaw.de
L. Kaleschke
G. Birnbaum
Institute of Oceanography, University of Hamburg, Bundesstr. 53, 20146 Hamburg, Germany
Max Planck Institute for Comparative and International Private Law, Mittelweg 187, 20148 Hamburg, Germany
Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
Melt ponds on sea ice strongly reduce the surface albedo and
accelerate the decay of Arctic sea ice. Due to different spectral
properties of snow, ice, and water, the fractional coverage of these
distinct surface types can be derived from multispectral sensors like
MODIS using a spectral unmixing algorithm. The unmixing was
implemented using a multilayer perceptron (MLP) to reduce
computational costs.
<br><br>
Arctic-wide melt pond fractions and sea ice concentrations are derived
from the level 3 MODIS surface reflectance product. The validation of
the MODIS melt pond data set was conducted with aerial photos from the
MELTEX campaign 2008 in the Beaufort Sea, data sets from the National
Snow and Ice Data Center (NSIDC) for 2000 and 2001 from four sites
spread over the entire Arctic, and with ship observations from the
trans-Arctic HOTRAX cruise in 2005. The root-mean-square errors (RMSE)
range from 3.8 % for the comparison with HOTRAX data, over 10.7 %
for the comparison with NSIDC data, to 10.3 % and 11.4 % for the
comparison with MELTEX data, with correlations coefficients ranging
from <i>R</i><sup>2</sup> = 0.28 to <i>R</i><sup>2</sup> = 0.45. The mean annual cycle of the melt
pond fraction for the entire Arctic shows a strong increase in June,
reaching a maximum of 15 % by the end of June. The zonal mean of
melt pond fractions indicates a dependence of the temporal development
of melt ponds from the geographical latitude, and has its maximum in
mid-July in latitudes between 80° and 88° N.
<br><br>
Furthermore, the MODIS results are used to estimate the influence of
melt ponds on retrievals of sea ice concentrations from passive
microwave data. Results from a case study comparing sea ice
concentrations from ASI-, NASA Team 2-, and Bootstrap-algorithms with
MODIS sea ice concentrations indicate an underestimation of around
40 % for sea ice concentrations retrieved with microwave algorithms.
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