Towards a long-term dataset of ELBARA-II measurements assisting SMOS level-3 land product and algorithm validation at the Valencia Anchor Station

R. Fernandez-Moran

Spain

Universitat de València

Tecnico superior de investigación. Departamento de Física de la Tierra y Termodinámica.

J. P. Wigneron

France

INRA

E. López-Baeza

Spain

Universitat de València

M. Miernecki

France

INRA

P. Salgado-Hernanz

Spain

Universitat de València

M.A. Coll

Spain

Universitat de València

Y. H. Kerr

France

CESBIO (Centre d'etudes spatiales de la biosphère)

M. Schwank

Switzerland

Swiss Federal Research Institute WSL

Submitted: 2014-04-15

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Accepted: 2015-03-03

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Published: 2015-06-26

DOI: https://doi.org/10.4995/raet.2015.2297
Funding Data

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Keywords:

brightness temperature, ELBARA-II, L-MEB, SMOS, SMOS level 3 data, soil moisture, soil roughness, Valencia Anchor Station, vegetation optical depth

Supporting agencies:

Project MIDAS-7/UVEG Productos y Aplicaciones Avanzados de SMOS y Futuras Misiones (Parte UVEG) from the Spanish Research Programme on Space

Spanish Ministry for Economy and Competitiveness.

Abstract:

The Soil Moisture and Ocean Salinity (SMOS) mission was launched on 2nd November 2009 with the objective of providing global estimations of soil moisture and sea salinity. The main activity of the Valencia Anchor Station (VAS) is currently to assist in a long-term validation of SMOS land products. This study focus on a level 3 SMOS data validation with in situ measurements carried out in the period 2010-2012 over the VAS. ELBARA-II radiometer is placed in the VAS area, observing a vineyard field considered as representative of a major proportion of an area of 50×50 km, enough to cover a SMOS footprint. Brightness temperatures (TB) acquired by ELBARA-II have been compared to those observed by SMOS at the same dates and time. They were also used for the L-MEB model inversion to retrieve soil moisture (SM), which later on have been compared to those provided by SMOS as level 3 data. A good correlation between both TB datasets was found, improving year by year, mainly due to the decrease of precipitations in the analyzed period and the mitigation of radio frequency interferences at L-band. The larger homogeneity of the radiometer footprint as compared to SMOS explains the higher variability of its TB. Periods of more intense precipitation (spring and autumn) also presented higher SM, which corroborates the consistency of SM retrieved from ELBARA-II’s observations. However, the results show that SMOS level 3 data underestimate SM as compared to ELBARA-II’s, probably due to the influence of the small soil fraction which is not cultivated in vineyards. SMOS estimations in descending orbit (6 pm) had better quality (higher correlation, lower RMSE and bias) than the ones in ascending orbit (6 am, when there is a higher soil moisture).
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