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Considering Combined or Separated Roughness and Vegetation Effects in Soil Moisture RetrievalsFor more than six years, the Soil Moisture and Ocean Salinity (SMOS) mission has provided multi angular and full-polarization brightness temperature (TB) measurements at L-band. Geophysical products such as soil moisture (SM) and vegetation optical depth at nadir (tau(sub nad)) are retrieved by an operational algorithm using TB observations at different angles of incidence and polarizations. However, the quality of the retrievals depends on several surface effects, such as vegetation, soil roughness and texture, etc. In the microwave forward emission model used in the retrievals (L-band Microwave Emission Model, L-MEB),soil roughness is modeled with a semi-empirical equation using four main parameters (Q(sub r), H(sub r), N(sub rp), with p = H or V polarizations). At present, these parameters are calibrated with data provided by airborne studies and in situ measurements made at a local scale that is not necessarily representative of the large SMOS footprints (43 km on average) at global scale. In this study, we evaluate the impact of the calibrated values of N(sub rp) and H(sub r) on the SM and tau(sub nad) retrievals based on SMOS TB measurements (SMOS Level 3 product) over the Soil Climate Analysis Network (SCAN) network located in North America over five years (2011-2015). In this study, Qr was set equal to zero and we assumed that N(sub rH)= N(sub rV). The retrievals were performed by varying N(sub rp) from −1 to 2 by steps of 1 and H(sub r) from 0 to 0.6 by steps of 0.1. At satellite scale, the results show that combining vegetation and roughness effects in a single parameter provides the best results in terms of soil moisture retrievals, as evaluated against the in situ SM data. Even though our retrieval approach was very simplified, as we did not account for pixel heterogeneity, the accuracy we obtained in the SM retrievals was almost systematically better than those of the Level 3 product. Improved results were also obtained in terms of optical depth retrievals. These new results may have key consequences in terms of calibration of roughness effects within the algorithms of the SMOS (ESA) and the SMAP (NASA) space missions.
Document ID
20170002031
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Parrens, Marie
(Centre d'Etudes Spatiales de la Biosphere Toulouse, France)
Wigernon, Jean-Pierre
(Centre INRA Bordeaux, France)
Richaume, Philippe
(Centre d'Etudes Spatiales de la Biosphere Toulouse, France)
Al Bitar, Ahmad
(Centre d'Etudes Spatiales de la Biosphere Toulouse, France)
Mialon, Arnaud
(Centre d'Etudes Spatiales de la Biosphere Toulouse, France)
Fernandez-Moran, Roberto
(Centre INRA Bordeaux, France)
Al-Yarri, Amen
(Centre INRA Bordeaux, France)
O'Neill, Peggy
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Kerr, Yann
(Centre d'Etudes Spatiales de la Biosphere Toulouse, France)
Date Acquired
March 7, 2017
Publication Date
November 10, 2016
Publication Information
Publication: International Journal of Applied Earth Observation and Geoinformation
Publisher: Elsevier
Volume: 55
ISSN: 0303-2434
Subject Category
Earth Resources And Remote Sensing
Report/Patent Number
GSFC-E-DAA-TN39645
Distribution Limits
Public
Copyright
Other
Keywords
full-polarization
vegetation optical depth

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