Soil moisture modelling of a SMOS pixel: interest of using the PERSIANN database over the Valencia Anchor Station

In the framework of Soil Moisture and Ocean Salinity (SMOS) Calibration/Validation (Cal/Val) activities, this study addresses the use of the PERSIANN-CCS<sup>1</sup>database in hydrological applications to accurately simulate a whole SMOS pixel by representing the spatial and temporal heterogeneity of the soil moisture fields over a wide area (50×50 km<sup>2</sup>). The study focuses on the Valencia Anchor Station (VAS) experimental site, in Spain, which is one of the main SMOS Cal/Val sites in Europe. <br><br> A faithful representation of the soil moisture distribution at SMOS pixel scale (50×50 km<sup>2</sup>) requires an accurate estimation of the amount and temporal/spatial distribution of precipitation. To quantify the gain of using the comprehensive PERSIANN database instead of sparsely distributed rain gauge measurements, comparisons between in situ observations and satellite rainfall data are done both at point and areal scale. An overestimation of the satellite rainfall amounts is observed in most of the cases (about 66%) but the precipitation occurrences are in general retrieved (about 67%). <br><br> To simulate the high variability in space and time of surface soil moisture, a Soil Vegetation Atmosphere Transfer (SVAT) model – ISBA (Interactions between Soil Biosphere Atmosphere) is used. The interest of using satellite rainfall estimates as well as the influence that the precipitation events can induce on the modelling of the water content in the soil is depicted by a comparison between different soil moisture data. Point-like and spatialized simulated data using rain gauge observations or PERSIANN – CCS database as well as ground measurements are used. It is shown that a good adequacy is reached in most part of the year, the precipitation differences having less impact upon the simulated soil moisture. The behaviour of simulated surface soil moisture at SMOS scale is verified by the use of remote sensing data from the Advanced Microwave Scanning Radiometer on Earth observing System (AMSR-E). We show that the PERSIANN database provides useful information at temporal and spatial scales in the context of soil moisture retrieval. <br><br> <br><br> <sup>1</sup>Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System – <a href="http://chrs.web.uci.edu/persiann"target="_blank">http://chrs.web.uci.edu/persiann</a&gt

Modelling soil moisture at SMOS scale by use of a SVAT model over the Valencia Anchor Station

16 páginas, 9 figuras, 5 tablas.The main goal of the SMOS (Soil Moisture and Ocean Salinity) mission is to deliver global fields of surface soil moisture and sea surface salinity using L-band (1.4 GHz) radiometry. Within the context of the Science preparation for SMOS, the Valencia Anchor Station (VAS) experimental site, in Spain, was chosen to be one of the main test sites in Europe for Calibration/Validation (Cal/Val) activities. In this framework, the paper presents an approach consisting in accurately simulating a whole SMOS pixel by representing the spatial and temporal heterogeneity of the soil moisture fields over the wide VAS surface (50x50 km(2)). Ground and meteorological measurements over the area are used as the input of a Soil-Vegetation-Atmosphere-Transfer (SVAT) model, SURFEX (Externalized Surface) - module ISBA (Interactions between Soil-Biosphere-Atmosphere) to simulate the spatial and temporal distribution of surface soil moisture. The calibration as well as the validation of the ISBA model are performed using in situ soil moisture measurements. It is shown that a good consistency is reached when point comparisons between simulated and in situ soil moisture measurements are made. Actually, an important challenge in remote sensing approaches concerns product validation. In order to obtain an representative soil moisture mapping over the Valencia Anchor Station (50x50 km(2) area), a spatialization method is applied. For verification, a comparison between the simulated spatialized soil moisture and remote sensing data from the Advanced Microwave Scanning Radiometer on Earth observing System (AMSR-E) and from the European Remote Sensing Satellites (ERS-SCAT) is performed. Despite the fact that AMSR-E surface soil moisture product is not reproducing accurately the absolute values, it provides trustworthy information on surface soil moisture temporal variability. However, during the vegetation growing season the signal is perturbed. By using the polarization ratio a better agreement is obtained. ERS-SCAT soil moisture products are also used to be compared with the simulated spatialized soil moisture. However, the lack of soil moisture data from the ERS-SCAT sensor over the area (45 observations for one year) prevented capturing the soil moisture variability.The authors wish to thank the European Space Agency (ESA), the Centre National d’Etudes Spatiales (CNES), the Centre National de la Recherche Scientifique – Institut National des Sciences de l’Univers (CNRS- INSU SIC) and the French National Programme TOSCA (Terre, Oc´eans, Surfaces Continentales et Atmosph´ere) for supporting this work. We also wish to thank the NASA National Snow and Ice Data Center (NSIDC) for providing AMSR-E data as well as the Institute for Photogrammetry and Remote Sensing, Vienna University of Technology, Vienna, Austria for providing the ERS-SCAT data. We thank also the Centre National de Recherches Météorologiques and Jean Christophe Calvet (CNRM) - Météo-France for the SURFEX model. The authors wish to thank also the Spanish Agency for Meteorology (AEMet) and to the Jucar River Basin Authority (CHJ) for the meteorological data. Edited by: N. Verhoest The publication of this article is financed by CNRS-INSU.Peer reviewe

The SMOS Soil Moisture Retrieval Algorithm

International audienceThe Soil Moisture and Ocean Salinity (SMOS) mission is European Space Agency (ESA's) second Earth Explorer Opportunity mission, launched in November 2009. It is a joint program between ESA Centre National d'Etudes Spatiales (CNES) and Centro para el Desarrollo Tecnologico Industrial. SMOS carries a single payload, an L-Band 2-D interferometric radiometer in the 1400-1427 MHz protected band. This wavelength penetrates well through the atmosphere, and hence the instrument probes the earth surface emissivity. Surface emissivity can then be related to the moisture content in the first few centimeters of soil, and, after some surface roughness and temperature corrections, to the sea surface salinity over ocean. The goal of the level 2 algorithm is thus to deliver global soil moisture (SM) maps with a desired accuracy of 0.04 m3/m3. To reach this goal, a retrieval algorithm was developed and implemented in the ground segment which processes level 1 to level 2 data. Level 1 consists mainly of angular brightness temperatures (TB), while level 2 consists of geophysical products in swath mode, i.e., as acquired by the sensor during a half orbit from pole to pole. In this context, a group of institutes prepared the SMOS algorithm theoretical basis documents to be used to produce the operational algorithm. The principle of the SM retrieval algorithm is based on an iterative approach which aims at minimizing a cost function. The main component of the cost function is given by the sum of the squared weighted differences between measured and modeled TB data, for a variety of incidence angles. The algorithm finds the best set of the parameters, e.g., SM and vegetation characteristics, which drive the direct TB model and minimizes the cost function. The end user Level 2 SM product contains SM, vegetation opacity, and estimated dielectric constant of any surface, TB computed at 42.5$^{circ}$, flags and quality indices, and other parameters o- interest. This paper gives an overview of the algorithm, discusses the caveats, and provides a glimpse of the Cal Val exercises

CNES and ESA CAROLS Airborne Campaigns at the Valencia Anchor Station and Los Monegros Site in the Framework of SMOS Validation

1 copia .pdf con Figs.Poster presentado en la European Geophysical Union. General Assembly 2011 celebrada en Viena del 03 al 08 de abril 2011. Session GI-1 on Geoscience Instrumentation.This communication will present the main results of a series of airborne campaigns conducted at the Valencia Anchor Station (VAS) and Los Monegros site using the CAROLS (Combined Airborne Radio-instruments for Ocean and Land Studies) radiometer on board the ATR 42 aircraft from M¶et¶eo-France. The main objective was to contribute to the implementation of the SMOS emission model L-MEB (L-band Microwave Emission model of the Biosphere) in the framework of the validation of SMOS land data and products. Speci¯cally, the objectives of the CAROLS campaigns were the following: Soil Moisture Validation Studies: Previous °ights at the VAS area took place in 2008 in the context of the ESA SMOS Validation Rehearsal Campaign 2008 (EMIRAD radiometer, L-band) over a control area of 10km£10km where intensive soil moisture data was acquired concurrently to airborne L-band measurements. One of the objectives of that campaign was to establish homogeneous units to characterize the average soil moisture of that area, and to investigate the possibility of extending the methodology to the whole SMOS validation pixel at the VAS site. The `homogeneous units' characterisation was studied and extended further in the context of CAROLS 2009, and validated during the CAROLS 2010 campaign. Radiometric Characterisation & SMOS Data Validation: The 10km £ 10km mentioned above is part of a larger area of » 50km £ 50km within the VAS SMOS validation pixel. For CAROLS 2009, °ights were performed over a 30km £ 50km area in order to examine the ra- diometric signature of other surfaces that are present in the VAS SMOS pixel but not in the 10km £ 10km control area examined in 2008 (mostly dense forests, matorral, and non-°at sur- faces). Main results of CAROLS 2009 will be presented in this communication, and the emphasis will be on comparing local to regional scale results given that CAROLS °ights were performed at 4000m above the surface. For 2010, lower altitude °ights (» 2200m a.s.l.) over an area of 20km£20km containing a large number of homogeneous units (`environmental units'), were used for validation of SMOS microwave model L-MEB. The preliminary results of this campaign will be presented in this communication, and the emphasis will be on the validation of the L-MEB model. In addition to the activities at the VAS site, °ights over Los Monegros' salt pans near Zaragoza were performed in the 2010 CAROLS Campaign to study their emissivity at L-band. Three playa-lakes (Guallar, La Playa, and Salineta) were sampled to measure gravimetric soil moisture and electrical conductivity.Peer reviewe

CNS and ESA CAROLS Airborne Campaigns at the Valencia Anchor Station and Los Monegros site in the framework of SMOS validation

2 ficheros .pdf, copias de la Presentación original (41 Pags.) y del Resumen ampliado (1 Pag.) en Libro de Actas del Congreso.This communication will present the main results of a series of airborne campaigns conducted at the Valencia Anchor Station (VAS) and Los Monegros site using the CAROLS (Combined Airborne Radio-instruments for Ocean and Land Studies) radiometer on board the ATR 42 aircraft from M¶et¶eo-France. The main objective was to contribute to the implementation of the SMOS emission model L-MEB (L-band Microwave Emission model of the Biosphere) in the framework of the validation of SMOS land data and products. Speci¯cally, the objectives of the CAROLS campaigns were the following:Soil Moisture Validation Studies: Previous °ights at the VAS area took place in 2008 in the context of the ESA SMOS Validation Rehearsal Campaign 2008 (EMIRAD radiometer, L-band) over a control area of 10km£10km where intensive soil moisture data was acquired concurrently to airborne L-band measurements. One of the objectives of that campaign was to establish homogeneous units to characterize the average soil moisture of that area, and to investigate the possibility of extending the methodology to the whole SMOS validation pixel at the VAS site. The `homogeneous units' characterisation was studied and extended further in the context of CAROLS 2009, and validated during the CAROLS 2010 campaign.Radiometric Characterisation & SMOS Data Validation: The 10km £ 10km mentioned above is part of a larger area of » 50km £ 50km within the VAS SMOS validation pixel. For CAROLS 2009, °ights were performed over a 30km £ 50km area in order to examine the ra- diometric signature of other surfaces that are present in the VAS SMOS pixel but not in the 10km £ 10km control area examined in 2008 (mostly dense forests, matorral, and non-°at sur- faces). Main results of CAROLS 2009 will be presented in this communication, and the emphasis will be on comparing local to regional scale results given that CAROLS °ights were performed at 4000m above the surface. For 2010, lower altitude °ights (» 2200m a.s.l.) over an area of 20km£20km containing a large number of homogeneous units (`environmental units'), were used for validation of SMOS microwave model L-MEB. The preliminary results of this campaign will be presented in this communication, and the emphasis will be on the validation of the L-MEB model.In addition to the activities at the VAS site, °ights over Los Monegros' salt pans near Zaragoza were performed in the 2010 CAROLS Campaign to study their emissivity at L-band. Three playa-lakes (Guallar, La Playa, and Salineta) were sampled to measure gravimetric soil moisture and electrical conductivity.Peer reviewe

Soil moisture estimates from the SMOS validation rehearsal campaign in Valencia using EMIRAD airborne measurements

International audienc

Morfología Fluvial.-The ESA SMOS Mission: Validation Activities at the Valencia Anchor Station

SUMMARY Since 2001, the Valencia Anchor Station (VAS) is being used for validation activities in the context of low spatial resolution Earth Observation Missions such as CERES (Clouds and the Earth’s Radiant Energy System), GERB (Geostationary Earth Radiation Budget), EPS (EUMETSAT Polar System), and is also being prepared for SMOS (Soil Moisture and Ocean Salinity). These missions have in common the low spatial resolution of their respective footprints (~50x50 km2) and the necessity of a well characterised and instrumented large scale area. The VAS has been selected as a primary validation site by the SMOS Mission. The reasonable homogeneous characteristics of the area make this site appropriate to undertake the validation of SMOS Level 2 land products (soil moisture (SM) and vegetation water content) during the Mission Commissioning Phase. A control area of 10x10 km2 was chosen to develop a network of ground SM measuring stations based on the definition of homogeneous physio-hydrological units attending to climatic, soil type, lithology, elevation, slope and vegetation cover conditions. The stations are linked via a wireless communication system to a central post accessible via internet. Area SM estimations are presently being compared to modelling products from ISBA – SURFEX. This paper shows the validation activities currently carried out at the VAS, especially the ESA SMOS Validation Rehearsal Campaign and the CNES CAROLS Scientific Airborne Campaign