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| Titel |
Effective soil moisture sampling depth of L-band radiometry |
| VerfasserIn |
M. J. Escorihuela, Y. H. Kerr, A. Chanzy, J. P. Wigneron |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019304
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| Zusammenfassung |
| In the near future two new satellite missions, the Soil Moisture and Ocean Salinity (SMOS)
and the Soil Moisture Active Passive (SMAP) will be providing for the first time global
mapping of surface soil moisture based on radiometric measurements at L-band. For
operational applications involving microwave radiometry, soil moisture is generally estimated
by inverting a simple model of soil microwave emission.
Several field and airborne campaigns have been carried out in order to test, validate and
better understand radiative transfer models at L-band. Some of them have shown that in order
to accurately model bare soil emission, it was necessary to adjust one parameter as a function
of soil moisture. In this way, an exponential and linear dependency of roughness
with soil moisture was found by Wigneron et al. 2001 and Escorihuela et al. 2007
respectively. While Schneeberger et al. 2004 fitted a coherent emission model with a
transition zone whose thickness depended also in soil moisture. A sensitivity of soil
roughness to soil moisture was also find for airborne L-band microwave data during the
COSMOS campaign Saleh et al. 2008. This kind of parameterizations pose the
problem that are site dependent and thus their application at the satellite scale is not
straight forward. Furthermore, they seem to indicate that the actual effective soil
moisture sampling depth is somewhat different that the one provided by the field
sensors.
The aim of this study is thus to analyze the influence of the soil moisture sampling
depth in the parameterizations of soil emission in microwave radiometry at L-band.
Brightness temperature, soil moisture and temperature profiles were measured over a
bare soil. A more detailed profile of surface soil moisture was obtained with a soil
heat and water flows mechanistic model. It was found that (1) the effective soil
moisture sampling depth is shallower than provided by widely used field moisture
sensors, (2) the effective soil moisture sampling depth depended on soil moisture. This
conclusions are crucial for the calibration and validation of remote sensing data at
L-band. A parameterization for soil moisture sampling depth at L-band is proposed. |
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