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| Titel |
Sea ice thickness temporal evolution during the Arctic freeze-up as seen by SMOS |
| VerfasserIn |
Lars Kaleschke, Xiangshan Tian-Kunze, Nina Maass |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049920
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| Zusammenfassung |
| ESA’s Soil Moisture and Ocean Salinity (SMOS) mission is measuring the brightness
temperature at 1.4 GHz correspondig to a wavelength of 21 cm. Such long electromagnetic
waves are emitted from well inside a low loss media such as pure ice. Sea ice contains liquid
brine of high conductivity and is therefore a lossy media. The relative brine volume and thus
the dielectric loss factor depends on the initial salt content and the ice temperature. As long as
parts of the microwave emission are emerging from the bottom ocean-ice interface
to the surface, the measured brightness temperature is a function of the sea ice
thickness.
In this study we analyse the intensity of radiation in seasonally ice covered Arctic waters
during the Autumn freeze-up from October to December 2010. In order to get an estimate of
the maximum ice thickness that can be retrieved from SMOS we calculate approximate sea
ice thicknesses from the cumulative freezing degree days by using NCEP reanalysis data and
compare these to the corresponding observed brightness temperature. A semi-empiric
model is used to calculate the ice thickness d = -1
γ ln(I1-I-
I1- I0) from the measured
intensity I and the three parameters I0, I1, and γ, with the intensity of the ice-free
ocean at the freezing point I0, the intensity of thick ice I1 and an attenuation factor
γ.
The analysis of the time series at certain positions of the NCEP grid cells allow the
following conclusions:
both intensities I0 = 98.8±1 K and I1 = 243.8±1.3 K exhibit little variability
over several weeks;
the intensity is monotonically increasing with the ice thickness as expected from
model simulations;
after the ice concentration has reached 100%, the 1.4 GHz intensity still increases
for about three weeks;
at a maximum ice thickness of about 0.5 m the intensity reaches I1 and further
ice growth does not increase the brightness temperature;
a constant γ - 9m-1 is a suitable choice for Arctic wide sea ice thickness
retrieval with SMOS during the freeze-up period. Correlations between the
cumulative freezing degree day thickness and the SMOS ice thickness are as high
as r2 = 0.96.
A more thorough validation and further improvement of the retrieval model is ongoing in
the framework of ESA’s Support to Science Element (STSE) SMOS Sea Ice Retrieval Study
(SMOSIce). |
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