Variable source areas, soil moisture and active microwave observations at Zwalmbeek and Coët-Dan

This chapter focuses on recent research to identify variable source areas from surface soil moisture dynamics observed at the catchment scale by means of active microwave images from satellites. It is hypothesized that variable source areas can be mapped if we can quantify the temporal variability of the surface soil moisture content. It is difficult to determine the soil moisture content from single synthetic aperture radar images because soil moisture, surface roughness, topography and vegetation all have a great effect on radar backscatter. However, seasonal soil moisture fluctuations can be studied by using multitemporal radar images. Two multitemporal image processing techniques are presented to map variable source areas. The first method computes the temporal standard deviation of radar backscatter. This leads to the definition of the so-called saturation potential index, which compares well with observed saturated areas. The second method makes use of a principal component analysis to separate the dominant effects, like topography, land use and soil moisture, on total radar backscatter. Again this leads to reliable mapping of the spatial patterns of variable source areas. Two humid catchments, the Zwalmbeek in Belgium and the Coët-Dan in France, are used in this study

Short-term implantation effects of a DCPD-based calcium phosphate cement

International audienceCalcium phosphate cements can be handled in paste form and set in a wet medium after precipitation of calcium phosphate crystals in the implantation site. Depending on the products entering into the chemical reaction leading to the precipitation of calcium phosphates, different phases can be obtained with different mechanical properties, setting times and injectability. We tested a cement composed of a powder, containing-tricalcium phosphate (-TCP) and sodium pyrophosphate mixed with a solution of phosphoric and sulphuric acids. The cement set under a dicalcium phosphate dihydrate (DCPD)-based matrix containing-TCP particles. This was injected with a syringe into a defect drilled in rabbit condyles, the control being an identical defect left empty in the opposite condyle. The condyles were analysed histologically 2, 6 and 18 weeks after implantation. After injection into the bone defect the cement set and formed a porous calcium phosphate structure. Two different calcium phosphate phases with different solubility rates could be identified by scanning electron microscopy (SEM) observation. The less-soluble fragments could be degraded by cell phagocytosis in cell compartments of low pH or integrated in the newly formed bone matrix. The degradation rate of the material was relatively high but compatible with the ingrowth of bone trabeculae within the resorbing material. The ossification process was different from the creeping substitution occurring at the ceramic contact. Bone did not form directly at the cement surface following the differentiation of osteoblasts at the material surface. The trabeculae came to the material surface from the edges of the implantation site. Bone formation in the implantation site was significantly higher than in the control region during the first week of implantation. In conclusion, this material set in situ was well tolerated, inducing a mild foreign-body reaction, which did not impair its replacement by newly formed bone within a few weeks

Naizin catchment

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Télédétection radar des zones saturées du bassin versant du Coët-Dan

[Departement_IRSTEA]GT [TR1_IRSTEA]GMA1-Fonctionnement hydrologique des bassins et des réseaux hydrographiquesInternational audienceAs interest shifts to the development of models for predicting runoff quality, identification of the source areas for runoff becomes increasingly important. Active microwave remote sensing has a unique potential for surveying source areas at the catchment scale. Thresholding of the back-scattering coefficient was initially proposed but proved unsatisfactory when applied to the ERS-1 SAR multitemporal images acquired during winter 1992 over the Coët-Dan catchment, concomitantly with ground observations. Difference images may, instead, allow the wettest part of the catchment to be identified provided that the tow images encompass a marked hydrological event. A saturation plot could not however be obtained for each date; the use of a pair of images may be further limited by the residual speckle (although carefully filtered using the multitemporal information) and a slight inaccuracy in the SAR image calibration. It is therefore argued that considering the whole temporal back-scatter profile would be, at present, a safer approach to the remote sensing of satured areas. The back-scatter temporal standard deviation appears, in this light, as a possible good indicator of the local saturation likelihood during the period of study : it is based on the fact that saturation develops on parts of the catchment that are wetter than the others through lateral recharge. Possible applications within the TOPMODEL framework are discussed.L'intérêt croissant pour le développement de modèles capables d'effectuer des prédictions en terme de qualité des eaux de ruissellement souligne la nécessité d'identifier les zones saturées à l'échelle d'un bassin versant. Et la télédétection radar semble bien l'outil idéal pour ce faire. Cependant, la méthode consistant à seuiller le coefficient de rétrodiffusion s'est révélée inadéquate sur les images ERS-1 acquises en hiver 1992 sur le bassin versant du Coët-Dan. Certaines différences d'images, en revanche, permettent d'identifier les zones les plus humides du bassin ; à condition qu'un événement hydrologique marqué se produise entre l'acquisition des deux images concernées. Néanmoins il ne semble pas possible de cartographier l'extension des zones saturées correspondant à chaque image. L'emploi d'un couple d'images est en outre limité par le speckle résiduel (quoique l'information multi-temporelle permette un filtrage efficace) ainsi que par une légère instabilité liée à la calibration des images radar. C'est pourquoi on préconise d'utiliser l'ensemble des images multi-temporelles disponibles. L'écart-type portant sur les variations temporelles du coefficient de rétrodiffusion nous apparaît comme un bon indicateur permettant d'apprécier la propension relative des différentes zones d'un bassin à se saturer : il s'appuie en effet sur la persistance de l'humidité qui caractérise les zones les plus propices à se saturer. On présente enfin différentes applications possibles dans le cadre de TOPMOEL

Dynamique du coefficient de rétrodiffusion du SAR d'ERS-1 en période de ressuyage des sols d'un petit bassin versant

[Departement_IRSTEA]GT [TR1_IRSTEA]GMA1-Fonctionnement hydrologique des bassins et des réseaux hydrographiquesThe backscattering coefficient evolution with respect to a reference date - selected after a rainy week - is displaied for the successive seven ERS-1 SAR images collected during the following no-rainy period over the Coët-Dan catchment (Brittany, France). The backscatter difference is computed at pixel scale thanks to a preliminary spatio-temporal filtering of the images. A marked differentiate signal behaviour is observed within the catchment that tends to support the hydrological variable source area concept.On présente l'évolution du coefficient de rétrodiffusion du SAR d'ERS-1 au sein d'un petit bassin versant breton en période de ressuyage. Sept images consécutives de Coët-Dan, filtrées spatio-temporellement et normalisées par rapport à une date de référence choisie juste après une semaine pluvieuse, montrent un comportement différentiel du signal radar - entre versants et bas-fonds - qui tend à confirmer le concept hydrologique de zones contributives préférentielles

On constraining the predictions of distributed models: the incorporation of fuzzy estimates of saturated areas into the calibration process

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Contraindre les prédictions d'un modèle distribué : l'incorporation d'une estimation floue des zones saturées au niveau du processus d'apprentissage

[Departement_IRSTEA]GT [TR1_IRSTEA]GMA1-Fonctionnement hydrologique des bassins et des réseaux hydrographiquesInternational audienceDistributed hydrological models are generally overparameterized, resulting in the possibility of multiple parameterizations from many areas of the parameter space, providing acceptable fits to be observed data. In this study, TOPMODEL parameterizations are conditioned on discharges, and then further conditioned on estimates of satured areas derived from ERS-1 snthetic aperture radar (SAR) images combined with the In (a/tan beta) topographic index, and compared to ground thruth saturation measurements made is one small subcatchment. The uncertainty associated with the catchment-wide predictions of saturated area is explicitly incorporated into the conditioning through the weighting of estimtes within a fuzzy set framework. The predictive uncertainty associated with the parameterizations is then assessed using the generalized likelihood uncertainty estimation (GLUE) methodology. It is shown that despite the uncertainty in the predictions of the saturated area the methodology can reject many previously acceptable range of a catchment average transmissivity parameter and of improved predictions of some discharge events.Les modèles hydrologiques distribués sont généralement surparamétrés, d'où une multitude de paramétrisations possibles, capables de reproduire convenablement les données observées. Dans cette étude, les paramétrisations de TOPMODEL sont tout d'abord conditionnées par un apprentissage sur les débits ; puis l'apprentissage se poursuit sur la base d'une estimation floue de l'extension des zones saturées déduite des images radar d'ERS-1 combinées à l'indice topographique, et comparée aux observations terrain d'un petit sous-bassin. L'incertitude associée aux prédictions de l'extension des zones saturées à l'échelle du bassin est explicitement incorporée dans le processus d'apprentissage du modèle à l'aide de mesures de vraisemblance. Les incertitudes sur la prédiction des débits sont alors évaluées à l'aide de la méthode GLUE. On montre, qu'en dépit de l'incertitude portant sur l'estimation des zones saturées, la méthode conduit à rejeter de nombreuses paramétrisations précédemment acceptables, à une réduction importante de la plage de variation du paramètre de transmissivité moyenne, et une amélioration sensible des prédictions du modèle