L-MEB: A simple model at L-band for the continental areas - Application to the simulation of a half-degree resolution and global scale data set.

L-band (1-2 GHz) microwave radiometry is the most relevant remote sensing technique to monitor soil moisture over land surfaces at the global scale. A synthetic multi-angular brightness temperature data set over land surfaces was simulated at 1.4 GHz, at a half-degree resolution and at the global scale (Pellarin et al., 2003a). This data set was built in order to develop and validate methods to retrieve soil moisture for near-future 1.4 GHz space missions. Brightness temperatures were computed using a simple model (L-MEB, L-band Microwave Emission of the Biosphere) based on radiative transfer equations. The L-MEB model is the result of an extensive review of the current knowledge of the microwave emission of various land covers (herbaceous and woody vegetation, frozen and unfrozen bare soil, snow, etc.) at L-Band considering that the model should be simple enough to be compatible with the simulation of a half-degree resolution and global scale data set. This model was parameterized for simulating L-band observations (in the 1-2 GHz range) but the model equations remain valid in a low frequency range (about 1 to 10 GHz) and thus including the L-, C- and X-bands. The soil and vegetation characteristics needed to initialize the L-MEB model were derived from existing land cover maps. Continuous simulations from a land-surface scheme for 1987 and 1988 provided time series of the main variables driving the L-MEB model: soil temperature at the surface and at depth, surface soil moisture, proportion of frozen surface soil moisture, and snow cover characteristics (depth, density, grain size, liquid water content). The different components of the emission model are described in the following sections. These sections present the general formulation of TB for a composite pixel and the microwave emission modules for soil, vegetation-covered surfaces, open water, snow-covered surfaces and atmospheric effects

Reconstitution par arbres de régression du rayonnement visible descendant horaire sur la France continentale, à partir de données in situ et de simulations : Spatialisation et vérification sur des données indépendantes

49 p.La nécessité de disposer sur toute la France de séries horaires de rayonnement visible descendant a mené à une reconstitution en deux étapes, à partir de paramètres facilement disponibles : * Une reconstitution en des points où sont disponibles la durée d'insolation, éventuellement des résultats de simulations Safran et des observations de nature et d'étendue des couches nuageuses. La méthode de reconstitution employée est basée sur des moyennes d'ensembles d'arbres de régression. Cette méthode permet de prendre en compte les non linéarités entre les divers intrants météorologiques. Elle est comparée avec d'autres ajustements non-linéaires. Les critères de choix entre les divers algorithmes statistiques sont : la qualité des résultats, la rapidité des apprentissages et la facilité des maintenances logicielles. On n'a pas rencontré de contradiction entre ces 3 critères. Des liaisons sont d'abord établies entre le rayonnement horaire et les autres paramètres météorologiques sur toutes les stations disposant de l'intégralité des données nécessaires. Elles sont d'abord testées par des méthodes de cross-validation sur ces mêmes stations, puis appliquées en tous les points disposant de mesure simultanées de durée d'insolation et de nébulosité (environ un par département). Ces pseudo-observations supplémentaires viennent compléter le réseau d'observations de rayonnement horaire, dont la répartition spatiale est très irrégulière. * La spatialisation à l'échelle de Safran (maille de 8'8km) est alors effectuée par krigeage ordinaire. La validation de ces traitements a porté sur 11 stations indépendantes, non gérées par Météo-France, et sur une période (2004) n'ayant servi à aucun réglage

Modelling LAI at a regional scale with ISBA-A-gs: comparison with satellite-derived LAI over southwestern France

International audienceA CO2-responsive land surface model (the ISBAA- gs model of M´et´eo-France) is used to simulate photosynthesis and Leaf Area Index (LAI) in southwestern France for a 3-year period (2001–2003). A domain of about 170 000 km2 is covered at a spatial resolution of 8 km. The capability of ISBA-A-gs to reproduce the seasonal and the interannual variability of LAI at a regional scale, is assessed with satellite-derived LAI products. One originates from the CYCLOPES programme using SPOT/VEGETATION data, and two products are based on MODIS data. The comparison reveals discrepancies between the satellite LAI estimates and between satellite and simulated LAI values, both in their intensity and in the timing of the leaf onset. The model simulates higher LAI values for the C3 crops than the satellite observations, which may be due to a saturation effect within the satellite signal or to uncertainties in model parameters. The simulated leaf onset presents a significant delay for C3 crops and mountainous grasslands. In-situ observations at a mid-altitude grassland site show that the generic temperature response of photosynthesis used in the model is not appropriate for plants adapted to the cold climatic conditions of the mountainous areas. This study demonstrates the potential of LAI remote sensing products for identifying and locating models' shortcomings at a regional scale

G-CLASS: geosynchronous radar for water cycle science - orbit selection and system design

The mission geosynchronous – continental land atmosphere sensing system (G-CLASS) is designed to study the diurnal water cycle, using geosynchronous radar. Although the water cycle is vital to human society, processes on timescales less than a day are very poorly observed from space. G-CLASS, using C-band geosynchronous radar, could transform this. Its science objectives address intense storms and high resolution weather prediction, and significant diurnal processes such as snow melt and soil moisture change, with societal impacts including agriculture, water resource management, flooding, and landslides. Secondary objectives relate to ground motion observations for earthquake, volcano, and subsidence monitoring. The orbit chosen for G-CLASS is designed to avoid the geosynchronous protected region and enables integration times of minutes to an hour to achieve resolutions down to ∼20 m. Geosynchronous orbit (GEO) enables high temporal resolution imaging (up to several images per hour), rapid response, and very flexible imaging modes which can provide much improved coverage at low latitudes. The G-CLASS system design is based on a standard small geosynchronous satellite and meets the requirements of ESA's Earth Explorer 10 call

CAROLS: A New Airborne L-Band Radiometer for Ocean Surface and Land Observations

The “Cooperative Airborne Radiometer for Ocean and Land Studies” (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD II radiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling correlation radiometer. It is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments (C-Band scatterometer—STORM, the GOLD-RTR GPS system, the infrared CIMEL radiometer and a visible wavelength camera). Following initial laboratory qualifications, three airborne campaigns involving 21 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in 2007, 2008 and 2009, in coordination with in situ field campaigns. In order to validate the CAROLS data, various aircraft flight patterns and maneuvers were implemented, including straight horizontal flights, circular flights, wing and nose wags over the ocean. Analysis of the first two campaigns in 2007 and 2008 leads us to improve the CAROLS radiometer regarding isolation between channels and filter bandwidth. After implementation of these improvements, results show that the instrument is conforming to specification and is a useful tool for Soil Moisture and Ocean Salinity (SMOS) satellite validation as well as for specific studies on surface soil moisture or ocean salinity

The EuroSTARRS-2001 aircraft campaign of the European Space Agency in support of the SMOS Mission

Ponencia presentada en: III Congreso de la Asociación Española de Climatología “El agua y el clima”, celebrado en Palma de Mallorca del 16 al 19 de junio de 2002.This work was carried out in the framework of the ESA-ESTEC contract no: 15949/02/NL/SF, and the Spanish National Space Research Programme Project no: PNE-009/2001-C-03

Rapport préliminaire sur les activités de la mission syro-française de Ras Shamra-Ougarit en 2007 et 2008 (67e et 68e campagnes)

Ce rapport présente les résultats préliminaires des travaux de terrain de la mission archéologique syro-française de Ras Shamra – Ougarit pour les campagnes de 2007 et 2008 qui se sont déroulées à Ras Shamra et sur plusieurs sites côtiers. Sur le tell de Ras Shamra, quatre opérations de fouilles ont été menées  : la poursuite du chantier du «  Rempart » et de celui de la «  Grand-rue », la reprise du dégagement du «  pont-barrage » sur le Nahr ed-Delbé et un nouveau chantier conjoint dans le secteur du «  Temple de Dagan ». Deux autres opérations ont commencé en 2008  : la prospection géomagnétique du tell et l’étude des techniques de taille de la pierre à Ougarit. Les travaux de la mission se sont portés également sur les sites côtiers du royaume d’Ougarit dans le cadre d’un nouveau programme conjoint visant à reconstituer l’évolution des paléo-environnements portuaires et la mobilité des paysages littoraux. La présentation des activités de terrain est complétée par une réflexion sur le plan de l’antique cité d’Ougarit et les premiers résultats de l’étude d’un atelier de travail du silex (Bronze récent final) mis au jour dans le chantier «  Grand-rue ».This report presents preliminary results from the Syrian-French archaeological excavations at Ras Shamra-Ugarit for the field seasons of 2007 and 2008, which took place at Ras Shamra and a number of coastal sites. At Ras Shamra tell, four excavations were undertaken : work continued at the sites of “Rempart” and “Grand-rue”, with further investigations of the “pont-barrage” on the Nahr ed-Delbe, in addition to a new joint site in the area of the “Temple de Dagan”. Two other projects began in 2008 : the geomagnetic survey of the tell and a study of the techniques of stone quarrying at Ugarit. The expedition’s work also extended to the coastal sites of the Kingdom of Ugarit within the framework of a new program looking to reconstruct the evolution of its harbours and mobility of the coastal landscapes. The presentation of the fieldwork activities is complemented by a piece looking at the plan of the ancient city of Ugarit and the first results of a study investigating a flint workshop (Late Bronze Age) unearthed at the “Grand-rue” site.خلاصة – يقدم هذا التقرير النتائج الأولية للبعثة الأثرية السورية-الفرنسية العاملة في موقع رأس شمرا- أوغاريت عن الأعمال تاميدانية في رأس شمرا خلال عامي 2007 و2008 وعدد من المواقع الساحلية. في موقع تل رأس شمرا، تمّ تنفيذ أربع عمليات حفر : إستكمال الحفريات في حقل « الأسوار» وحقل « الشارع الكبير»، ومتابعة أعمال الكشف على « الجسر-السد» على نهر الدلبة، بالإضافة الى المباشرة في تنفيذ تنقيب مشترك في حقل معبد « داغان». بالمقابل ثم المباشرة بتنفيذ عمليتين في أوغاريت خلال عام 2008 : عمليات مسح جيومغناطيسية للتل، ودراسة تقنية تتعلّق بطرق تقصيب وتشذيب أحجار البناء. تضمّنت أعمال البعثة أيضاً، العمل على المواقع الساحلية لمملكة أوغاريت وذلك ضمن إطار برنامج جديد مشترك يهدف إلى وضع تصوّر لتطوّر الظروف البيئية للمرافئ بالأضافة إلى تصوّر عام لكينونة الشريط الساحلي. إستكمال عرض الأعمال الميدانية بوضع تصوّر لمخطط المدينة القديمة لأوغاريت والنتائج الأولية لمشغل للأدوات الصوانية إكتشف في حقل « الشارع الكبير» يعود إلى عصر البرونز الحديث النهائي

Widespread occurrence of anomalous C-band backscatter signals in arid environments caused by subsurface scattering

Backscatter measured by scatterometers and Synthetic Aperture Radars is sensitive to the dielectric properties of the soil and normally increases with increasing soil moisture content. However, when the soil is dry, the radar waves penetrate deeper into the soil, potentially sensing subsurface scatterers such as near-surface rocks and stones. In this paper we propose an exponential model to describe the impact of such subsurface scatterers on C-Band backscatter measurements acquired by the Advanced Scatterometer (ASCAT) on board of the METOP satellites. The model predicts an increase of the subsurface scattering contributions with decreasing soil wetness that may counteract the signal from the soil surface. This may cause anomalous backscatter signals that deteriorate soil moisture retrievals from ASCAT. We test whether this new model is able to explain ASCAT observations better than a bare soil backscatter model without a subsurface scattering term, using k-fold cross validation and the Bayesian Information Criterion for model selection. We find that arid landscapes with Leptosols and Arenosols represent ideal environmental conditions for the occurrence of subsurface scattering. Nonetheless, subsurface scattering may also become important in more humid environments during dry spells. We conclude that subsurface scattering is a widespread phenomenon that (i) needs to be accounted for in active microwave soil moisture retrievals and (ii) has a potential for soil mapping, particularly in arid and semi-arid environments

Clarifications on the "Comparison Between SMOS, VUA, ASCAT, and ECMWF Soil Moisture Products Over Four Watersheds in U.S."

In a recent paper, Leroux et al. compared three satellite soil moisture data sets (SMOS, AMSR-E, and ASCAT) and ECMWF forecast soil moisture data to in situ measurements over four watersheds located in the United States. Their conclusions stated that SMOS soil moisture retrievals represent "an improvement [in RMSE] by a factor of 2-3 compared with the other products" and that the ASCAT soil moisture data are "very noisy and unstable." In this clarification, the analysis of Leroux et al. is repeated using a newer version of the ASCAT data and additional metrics are provided. It is shown that the ASCAT retrievals are skillful, although they show some unexpected behavior during summer for two of the watersheds. It is also noted that the improvement of SMOS by a factor of 2-3 mentioned by Leroux et al. is driven by differences in bias and only applies relative to AMSR-E and the ECWMF data in the now obsolete version investigated by Leroux et al