Implementation of a satellite-based prognostic daily surface albedo depending on soil wetness : impact study in SURFEX modelling platform over France

The main objective of the thesis is to develop a prognostic surface albedo of the visible spectrum and near infrared and assess its impact on the energy balance and hydrology in the modelling platform of SURFEX. First, a statistical approach has generated a global climate albedo product at 0.05 ° for bare soil and vegetation using multiple years 8 -day MODIS onboard TERRA and AQUA satellites heliosynchronous data. Then, an original method has been developed to reduce temporal resolution of MODIS 500m albedo to daily. The result is validated against in situ measurements as well as daily albedo from geostationary satellite MSG / SEVIRI Land SAF project after projection of MODIS. Then a method of separating albedo of bare soil and vegetation is applied to the datasets of the two satellite systems. Using a threshold of vegetation cover, a calibration of the albedo bare soil with measured soil moisture is derived from 2007 to 2010 for 12 SMOSMANIA stations over southwestern France. We derived a parameterization of the albedo of bare soil with moisture to make the climate changing albedo. The albedo and simulated happens to be very well correlated with observations from space, which helps to explain the albedo variations at very short notice. To change seasonally albedo, a simple parameterization of canopy albedo derived from detailed radiative transfer code PROSAIL is used. The variables are the albedo of the sheet, canopy geometry and chlorophyll content. In order to be sensitive to chlorophyll, the study is based on an albedo at 560 nm. The theoretical approach is validated with MODIS satellite data for the site Majadas (Spain). The next step is to conduct an impact study of this new predictive albedo on the energy balance and hydrology within SURFEX over France and highlighting effects on temperature. More preliminary restricted to a SMOSMANIA station, an assimilation scheme is developed for surface albedo together with the leaf area index LAI and surface moisture. This effects an improvement in the prescribed LAI at the beginning of crop growth

Implementation of a satellite-based prognostic daily surface albedo depending on soil wetness : impact study in SURFEX modelling platform over France

L'objectif de la thèse est de développer un albédo de surface journalier pronostique dans les modèles météorologiques et d’évaluer son impact pour le bilan d'énergie et l'hydrologie dans la plate-forme de modélisation SURFEX sur le domaine France. En premier lieu, un albédo climatologique est à ce jour considéré dans SURFEX. Il est analysé dans cette étude par rapport aux albédos quotidiens de SEVIRI et MODIS dont ce dernier est obtenu à partir d'une méthode originale que l'on valide. Ensuite, une méthode est développée pour obtenir des albédos du sol et de la végétation de façon séparée à la fois statiquement, donc sur une base climatologique, puis dynamiquement en s'appuyant sur plusieurs années de données du satellite MODIS. Une fois réglé l'albédo du sol journalier, il est recherché une calibration avec l'humidité du sol nu à l'aide des données du réseau de stations sol SMOSMANIA du sud-ouest de la France. Il est montré que l'on peut prédire l'évolution de l'albédo de surface, par comparaison avec les observations spatiales avec l'humidité seule dans la limite d'une végétation faiblement couvrante. Cet albédo simulé est complété par celui de la végétation seule à partir d'une paramétrisation simplifiée du code de transfert radiatif PROSAIL. L'approche théorique est validée avec les données du site de Majadas pour lequel on montre que l'on sait simuler le cycle d'évolution de l'albédo total avec prise en compte de la chlorophylle au niveau de la feuille. En dernier lieu, il a été réalisé une étude d'impact du nouveau albédo évolutif sur le bilan d'énergie et l'hydrologie dans SURFEX sur la France. Il est aussi mis en place une assimilation de l'albédo conjointement avec l'indice foliaire et l'humidité superficielle, ce qui a des effets positifs pour le cas des végétations qui ne sont pas trop denses. ABSTRACT : The main objective of the thesis is to develop a prognostic surface albedo of the visible spectrum and near infrared and assess its impact on the energy balance and hydrology in the modelling platform of SURFEX. First, a statistical approach has generated a global climate albedo product at 0.05 ° for bare soil and vegetation using multiple years 8 -day MODIS onboard TERRA and AQUA satellites heliosynchronous data. Then, an original method has been developed to reduce temporal resolution of MODIS 500m albedo to daily. The result is validated against in situ measurements as well as daily albedo from geostationary satellite MSG / SEVIRI Land SAF project after projection of MODIS. Then a method of separating albedo of bare soil and vegetation is applied to the datasets of the two satellite systems. Using a threshold of vegetation cover, a calibration of the albedo bare soil with measured soil moisture is derived from 2007 to 2010 for 12 SMOSMANIA stations over southwestern France. We derived a parameterization of the albedo of bare soil with moisture to make the climate changing albedo. The albedo and simulated happens to be very well correlated with observations from space, which helps to explain the albedo variations at very short notice. To change seasonally albedo, a simple parameterization of canopy albedo derived from detailed radiative transfer code PROSAIL is used. The variables are the albedo of the sheet, canopy geometry and chlorophyll content. In order to be sensitive to chlorophyll, the study is based on an albedo at 560 nm. The theoretical approach is validated with MODIS satellite data for the site Majadas (Spain). The next step is to conduct an impact study of this new predictive albedo on the energy balance and hydrology within SURFEX over France and highlighting effects on temperature. More preliminary restricted to a SMOSMANIA station, an assimilation scheme is developed for surface albedo together with the leaf area index LAI and surface moisture. This effects an improvement in the prescribed LAI at the beginning of crop growth

Exploiting earth observation data products for mapping local climate zones

Earth Observation (EO) systems and the advances in remote sensing technology increase the opportunities for monitoring the thermal behaviour of cities. Several parameters related to the urban climate can be quantified from EO data products, providing valuable support for advanced urban studies and climate modelling. In this study, remote sensing techniques are applied to derive quantitative information necessary to identify the Local Climate Zones (LCZ). Parameters like the pervious and impervious surface fraction, the surface albedo, the building density, the mean building/tree height and the sky view factor are quantified and used to map possible zones with homogeneous thermal characteristics, considered as LCZ

The variation of apparent crown size and canopy heterogeneity across lowland Amazonian forests

Aim: The size structure of a forest canopy is an important descriptor of the forest environment that may yield information on forest biomass and ecology. However, its variability at regional scales is poorly described or understood because of the still prohibitive cost of very high-resolution imagery as well as the lack of an appropriate methodology. We here employ a novel approach to describe and map the canopy structure of tropical forests. Location: Amazonia. Methods: We apply Fourier transform textural ordination (FOTO) techniques to substamples of very high-resolution satellite imagery freely available through virtual globe software (e.g. Google Earth ®) to determine two key structural variables: apparent mean crown size and heterogeneity in crown size. A similar approach is used with artificial forest canopy images generated by the light interaction model (discrete anisotropic radiative transfer, DART) using three-dimensional stand models. The effects of sun and viewing angles are explored on both model and real data. Results: It is shown that in the case of canopies dominated by a modal size class our approach can predict mean canopy size to an accuracy of 5%. In Amazonia, we could evidence a clear macrostructure, despite considerable local variability. Apparent crown size indeed consistently increases from about 14 m in wet north-west Amazonia to more than 17 m for ares of intermediate dry season length (1-3 months) in south and east Amazonia, before decreasing again towards the ecotone with the Cerrado savanna biome. This general trend reflects the known variation of other forest physiognomic properies (height) reported for South America and Africa. Some regions show significantly greater canopy heterogeneity, a feature that may be related to substratum, perturbation rate and/or forest turnover rate. Main conclusion: Our results demonstrate the feasibility and interest of large-scale assessment of rain forest canopy structure

Measles outbreaks in the Mozambican refugee camps in Malawi: the continued need for an effective vaccine.

To access this article, click on "Additional Links"Between November 1988 and January 1989, measles outbreaks occurred in 11 Mozambican refugee camps in Malawi with five camps principally affected. A total of 1214 cases were reported. Despite the reduction of the age of measles vaccination to six months in 1987, attack rates were highest in children aged 6-9 months (10-26%); rates were also high in the 0-5 month age group (3-21%). The case-fatality rate was high among children less than five years old (15-21%). Children were being inappropriately vaccinated, either being vaccinated at less than six months of age (2-29%) or failing to receive a second dose if vaccinated at six months (0-25%). With vaccine coverage between 66-87%, vaccine efficacy in children less than five years old was estimated to be more than 90% in the camps principally affected. Reduction of the age of vaccination leads to logistical problems in vaccine delivery in refugee situations. These outbreaks again indicate the need to improve vaccine coverage with the existing Schwarz vaccine, and also highlight the urgent need for an effective single dose measles vaccine for children less than nine months of age

Modélisation du Transfert radiatif Atmosphérique dans le modèle DART

International audienceLe modèle DART (Discrete Anisotropic Radiative Transfer) simule le transfert radiatif (T.R.) 3D dans le système "Terre – Atmosphère". Les paysages terrestres sont urbains ou naturels, avec relief. DART opère dans le domaine optique de l'ultraviolet à l'infrarouge thermique. Il simule des images de télédétection spatiale, pour toute configuration instrumentale et expérimentale (direction de visée, résolution spatiale, etc.). Il simule aussi des spectres et le bilan radiatif 3D. La précision radiométrique est un objectif essentiel de DART. Cette précision implique une modélisation précise du couplage "Terre - Atmosphère". Récemment, le T.R. atmosphérique a fait l'objet d'une grande amélioration en terme de précision et de flexibilité. Son algorithme s'appuie sur un échantillonnage spécifique de l'atmosphère et sur des fonctions de transfert atmosphérique pour réduire les temps de calcul. Ainsi, comparé au modèle atmosphérique ModTran, la précision de DART, en terme d'erreur relative, est passée de 6.5% à 1.3%

Introduction of clouds in dart model

International audienceClouds cover around two thirds of the Earth’s surface. Most of them are thick enough to influence the radiative budget of our planet: they increase the top of atmosphere (TOA) exitance and they alter the bottom of atmosphere (BOA) direct and diffuse irradiance. However, most radiative transfer models dedicated to Earth surfaces, such as DART (Discrete Anisotropic Radiative Transfer), simulate only cloudless atmospheres. We recently introduced clouds in DART in order to improve the modelling of weather for remote sensing simulations. In this implementation, clouds were characterized with user specified optical properties and vertical distribution. They were modelled as layered one-dimensional medium that coexists with gases and aerosols. The atmospheric radiative transfer modelling relies on the discrete ordinate method already in DART. In addition, an iterative inversion procedure was designed to test this improvement with field measurements during two cloudy days at Lamasquère meteorological station (France). Specifically, it derives time-series of atmosphere parameters from time-series of BOA solar irradiance measurements. These inversed atmospheric parameters were used to simulate total and diffuse BOA irradiance in PAR (Photosynthetically Active Radiation) domain. The comparison of time-series of measured and DART simulated PAR irradiance lead to very encouraging results (mean relative error ~ 8% for total irradiance and ~20% for diffuse irradiance). It stresses the potential of DART to accurately simulate irradiance in cloudy days