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| Titel |
Influence of vegetation on SMOS mission retrievals |
| VerfasserIn |
K. Lee, Eleanor J. Burke, W. Shuttleworth, R. Harlow |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 6, no. 2 ; Nr. 6, no. 2, S.153-166 |
| Datensatznummer |
250003451
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| Publikation (Nr.) |
 copernicus.org/hess-6-153-2002.pdf |
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| Zusammenfassung |
| Using the proposed Soil
Moisture and Ocean Salinity (SMOS) mission as a case study, this paper
investigates how the presence and nature of vegetation influence the values of
geophysical variables retrieved from multi-angle microwave radiometer
observations. Synthetic microwave brightness temperatures were generated using a
model for the coherent propagation of electromagnetic radiation through a
stratified medium applied to account simultaneously for the emission from both
the soil and any vegetation canopy present. The synthetic data were calculated
at the look-angles proposed for the SMOS mission for three different
soil-moisture states (wet, medium wet and dry) and four different vegetation
covers (nominally grass, crop, shrub and forest). A retrieval mimicking that
proposed for SMOS was then used to retrieve soil moisture, vegetation water
content and effective temperature for each set of synthetic observations. For
the case of a bare soil with a uniform profile, the simpler Fresnel model
proposed for use with SMOS gave identical estimates of brightness temperatures
to the coherent model. However, to retrieve accurate geophysical parameters in
the presence of vegetation, the opacity coefficient (one of two parameters used
to describe the effect of vegetation on emission from the soil surface) used
within the SMOS retrieval algorithm needed to be a function of look-angle,
soil-moisture status, and vegetation cover. The effect of errors in the initial
specification of the vegetation parameters within the coherent model was
explored by imposing random errors in the values of these parameters before
generating synthetic data and evaluating the errors in the geophysical
parameters retrieved. Random errors of 10% result in systematic errors (up to
0.5°K, 3%, and ~0.2 kg m-2 for temperature, soil moisture, and
vegetation content, respectively) and random errors (up to ~2°K, ~8%,
and ~2 kg m-2 for temperature, soil moisture and vegetation content,
respectively) that depend on vegetation cover and soil-moisture status.
Keywords: passive microwave, soil moisture, vegetation, SMOS, retrieval |
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