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Title: Soil Moisture Active and Passive Microwave Products: Intercomparison and Evaluation over a Sahelian Site

Author
item GRUHIER, CLIARE - Center For The Study Of The Biosphère From Space(CESBIO)
item DE ROSNAY, PATRICIA - European Centre For Medium-Range Weather Forecasts (ECMWF)
item HASENHAUER, STEFAN - Vienna University Of Technology
item Holmes, Thomas
item DE JEU, RICHARD - Vrije University
item KERR, YANN - Center For The Study Of The Biosphère From Space(CESBIO)
item MOUGIN, ERIC - Center For The Study Of The Biosphère From Space(CESBIO)
item NJOKU, ENI - Jet Propulsion Laboratory
item TIMOUK, FRANK - Center For The Study Of The Biosphère From Space(CESBIO)
item WAGNER, WOLFGANG - Vienna University Of Technology
item ZRIBI, MEHREZ - Center For The Study Of The Biosphère From Space(CESBIO)

Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2010
Publication Date: 4/21/2010
Citation: Gruhier, C., De Rosnay, P., Hasenhauer, S., Holmes, T.R., De Jeu, R., Kerr, Y., Mougin, E., Njoku, E., Timouk, F., Wagner, W., Zribi, M. 2010. Soil moisture active and passive microwave products: Intercomparison and evaluation over a Sahelian site. Hydrology and Earth System Sciences. 14:141-156.

Interpretive Summary: Surface soil moisture (SSM) is a key variable which controls the water and energy exchanges at the soil-vegetation-atmosphere interface. Previously, it has been shown that the SSM feedback with precipitation is very strong in three regions: the US Great Plains, Asia and West Africa. In particular, the Sahel region of West Africa it shown that SSM and land surface processes influence meso-scale convective systems dynamics. This paper provides an inter-comparison and evaluation of five surface soil moisture products over the Sahel region, as obtained from three different satellites using active and passive microwave remote sensing approaches. Three satellite products derived from passive microwave remote sensing (two from AMSR-E, one from TMI) and two products provided from active microwave remote sensing (both from ERS) were used. Ground station measurements from three different sites in the Gourma region of Sahel were used to validate these products. This first inter-comparison of active and passive microwave soil moisture products over Sahel clearly points out that both active and passive low frequencies remote sensing approaches are highly suitable to provide quantitative estimations of surface soil moisture. Best performances are obtained from passive microwave sensors. The analysed products together present a record of almost 20 years and will be used to study the role of land-atmosphere feedbacks in the regional climate of the Sahel. A better understanding of these mechanisms is expected to improve the weather prediction in areas like the Sahel but also the US Great Plains with important eventual benefits for agriculture.

Technical Abstract: This paper presents a comparison and an evaluation of five soil moisture products based on satellite-based passive and active microwave measurements. Products are evaluated for 2005-2006 against ground measurements obtained from the soil moisture network deployed in Mali (Sahel) in the framework of the African Monsoon Multidisciplinary Analysis project. It is shown that the accuracy of the soil moisture products is sensitive to the retrieval approach as well as to the sensor type (active or passive) and to the signal frequency (from 5.6 GHz to 18.8 GHz). The spatial patterns of surface soil moisture are compared between the different products at meso-scale (14.5±N - 17.5±N and 2±W- 1±W). A general good consistency between the different satellite soil moisture products is shown in terms of meso-scale spatial distribution, in particular after convective rainfall occurrences. Soil moisture values provided by the different products are compared to ground measurements time series. Although soil moisture products obtained from satellite generally over-estimate soil moisture values during the dry season, most of them capture soil moisture temporal variations in good agreement with ground stations measurements.