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CATDS - Centre Aval de Traitement des Données SMOS 
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Name of product : SM_SCIE_MIR_CLF4HR (SMOS/SCIEntific/MIRas/Catds/Land/Full pol/Level4/RougHness (HR))

Description : Global map of Soil Roughness based on SMOS L-Band Brightness temperatures

Version: 001

Content:
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      - Soil Roughness

Based on:
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     -	SMOS L3 TB
     

contacts:
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jeanpierre.wigneron@ & marie.parrens@cesbio.cnes.fr 

Reference:
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Parrens, Marie; Wigneron, Jean-Pierre; Richaume, Philippe; Mialon, Arnaud; Al Bitar, Ahmad; 
Fernandez-Moran, Roberto; Al-Yaari, Amen; Kerr, Yann H; ,Global-scale surface roughness effects 
at L-band as estimated from SMOS observations,Remote Sensing of Environment,181,,122-136,2016,Elsevier


Abstract from reference
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Abstract: The Soil Moisture and Ocean Salinity (SMOS) mission is the first satellite dedicated 
to providing global surface soil moisture products. SMOS operates at L-band (1.4 GHz) and, at 
this frequency, the signal not only depends on soil moisture and vegetation optical depth but
 is also significantly affected by surface effects and, in particular, by the soil roughness.
 However, when dense vegetation is present, the L-band signal is poorly sensitive to the surface
 effects. First, by using multiple regressions between soil moisture (SM) and brightness temperature (TB) 
at different incidence angles and polarizations, the SMOS sensitivity to the surface effects was 
evaluated. A global-scale map of SMOS sensitivity to the surface effects was computed and showed 
that, for 87% of the land surface, the SMOS observations were sensitive to these effects, while 
very low sensitivity to the surface effects was estimated over 13% of the land surfaces. For instance,
over broadleaf evergreen forest (mainly the Amazon and Congo forests), SMOS was sensitive to the surface
effects over only half of the pixels considered. In a second step, in L-MEB (L-band Microwave Emission
 of the Biosphere), the forward emission model of the SMOS algorithm, the vegetation and roughness effects 
were combined in a single parameter, referred to as TR in this study. By inverting L-MEB, SM and TR were
retrieved at global scale from the SMOS Level 3 (L3) TB observations during 2011. Assuming a linear
relationship between TR and the Leaf Area Index (LAI) obtained from MODIS data, the effects of roughness (Hr)
and vegetation were decoupled and a global map of soil roughness effects was estimated. It was found that
the spatial pattern of the Hr values could be related to the main vegetation types. Higher values of roughness 
(Hr = 0.32–0.39) were obtained for forests (broadleaf evergreen, deciduous and mixed coniferous) while lower 
values (Hr = 0.14–0.16) were obtained for deserts, shrubs and bare soils. Intermediate values (Hr = 0.20–0. 23)
 were obtained over grasslands, tundra and cultivated land. Over vegetation biomes composed of forests and wooded 
grasslands, the Hr values were mainly correlated to the vegetation density (r ~ 0.55). For deserts, shrubs and 
bare soils, the Hr values were mainly correlated to the topography slopes (r ~ 0.53). The global maps presented
 in this study could lead to improved retrievals of soil moisture and vegetation optical depth for present and 
future microwave remote sensing missions such as SMOS and Soil Moisture Active Passive (SMAP).
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