Search results for "NDVI"
showing 10 items of 56 documents
A combined optical-microwave method to retrieve soil moisture over vegetated areas
2011
A simple approach for correcting for the effect of vegetation in the estimation of the surface soil moisture (wS) from L-band passive microwave observations is presented in this study. The approach is based on semi-empirical relationships between soil moisture and the polarized reflectivity including the effect of the vegetation optical depth which is parameterized as a function of the normalized vegetation difference index (NDVI). The method was tested against in situ measurements collected over a grass site from 2004 to 2007 (SMOSREX experiment). Two polarizations (horizontal/vertical) and five incidence angles (20◦, 30◦, 40◦, 50◦, and 60◦) were considered in the analysis. The best wS est…
L'imagerie multispectrale embarquée pour caractériser la croissance et l'état sanitaire du feuillage de la vigne
2015
Multispectral imaging systems are widely used in remote sensing and applied to viticulture context for the canopy characterization. This technique is not used in proximal sensing, to characterize vineyard foliage. Yet the results of field tests led in fixed position have revealed its capacity to estimate the leaf area. The aim of this project is to assess the suitable of a multispectral imaging system as an embedded sensor for vine foliage characterization. To this end, a multispectral camera acquiring visible and near-infrared images and a Greenseeker RT-100 apparatus providing an NDVI (Normalized Difference Vegetation Index), were installed on a track laying tractor. It was equipped with …
Végétation de début de saison en Afrique du Sud semi aride : effets mémoires et conditions environnementales
2010
Dans les régions semi arides africaines (précipitations annuelles entre 200 et 600 mm), les variations interannuelles du NDVI sont largement contrôlées par celles des précipitations de l'année. Toutefois, les valeurs de NDVI dépendent également de conditions ayant prévalu par deçà la saison sèche (Martiny et al., 2005 ; Camberlin et al., 2007). En Afrique du Sud, la reprise de l'activité de la végétation suit avec un à deux mois de retard le retour des pluies. Les variations interannuelles du NDVI de début d'été dépendent essentiellement des précipitations de début de saison des pluies. Mais les variations résiduelles, effets des pluies synchrones enlevés, mettent en évidence un double effe…
Cycle saisonnier du NDVI dans le Nord-Cameroun et relations avec la pluviométrie (1982-2002)
2008
National audience; Résumé : Dans ce travail, il est question, de juger de la pertinence de l'indice de végétation normalisé (NDVI) pour l'étude de l'évolution du couvert végétal à petite échelle spatiale. Le choix de notre zone d'étude est porté dans le Nord-Cameroun qui, comparativement à la partie méridionale du pays, présente une végétation plus dépendante des conditions pluviométriques. Il en ressort que l'utilisation du NDVI est plus appropriée dans la région située au-dessus du 9e parallèle où la végétation démarre avec un retard de 3 à 9 décades par rapport au début de la saison des pluies. Dans la région soudanienne située au sud de cette latitude, le NDVI est plus représentatif des…
Étude multi-échelles des précipitations et du couvert végétal au Cameroun : Analyses spatiales, tendances temporelles, facteurs climatiques et anthro…
2011
Due to its shape and location (2°N-13°N - 8°E-16°E; proximity of the Atlantic Ocean), Cameroon is characterized by a panel of cross-regional climate encountered widely in tropical Africa. Over the region, the decrease rainfall during the second half of the last century has been shown to be associated with stronger recurrence of drier periods, specifically in the core of the rainy season. These conditions have favored the degradation of vegetation cover, driven by socioeconomic and demographic constraints. The substantial impacts on human activities and local society highlight the need to better understand how climate and environmental dynamics do interact locally. The aim of this study is t…
Observación multiescala de la cubierta vegetal mediante Teledetección. Aplicación a Castilla- La Mancha
2014
Uno de los principales objetivos de los sistemas de satélites de observación de la Tierra, es el seguimiento de la vegetación y de sus cambios. Dependiendo de cual sea la escala de interés, la resolución espacial y temporal que proporciona un solo satélite, con frecuencia, no va a ser es suficiente. Esto ocurre en los cultivos agrícolas, que revisten gran importancia y cuya dinámica de cambio requiere para su seguimiento alta resolución espacial y alta frecuencia temporal durante el periodo de crecimiento del cultivo. Este trabajo aborda la obtención de densas series temporales densas de imágenes de alta resolución espacial suficiente para el seguimiento de estas cubiertas. Para ello desarr…
Association between Asthma Control and Exposure to Greenness and Other Outdoor and Indoor Environmental Factors: A Longitudinal Study on a Cohort of …
2022
Achieving and maintaining asthma control (AC) is the main goal of asthma management. Indoor and outdoor environmental factors may play an important role on AC. The aim of this longitudinal study was to evaluate the association between AC and exposure to greenness and other outdoor or indoor environmental factors in a cohort of asthmatic children. This study involved 179 asthmatic children (5–16 years). Parents were interviewed through a modified version of the SIDRIA questionnaire. AC was assessed at each visit. Exposure to greenness was measured using the normalized difference vegetation index (NDVI). A logistic regression model was applied for assessing risk factors for uncontrolled…
Different trends of neighboring populations of Lesser Kestrel: Effects of climate and other environmental conditions
2019
The sensitivity of population trends to the climate and environment is generally considered a species-specific trait. However, evidence that populations may show different responses to the climate and environmental conditions is growing. Whether this differential sensitivity may arise even among neighboring populations remains elusive. We compared the trends of two neighboring populations of the Lesser Kestrel Falco naumanni, using data from a 12-year survey of 158 colonies in Sicily, Italy; the two populations inhabiting a lowland and an highland area, respectively. Population trends were modeled through the TRIM algorithms implemented in R (package rtrim). A reversed U-shaped population t…
Study of vegetation evolution in Sicily using time series analysis of remote sensing and climatic data.
2007
During last 10 years, several studies confirmed that drought phenomena are affecting southern Mediterranean areas. One of the effects of a persistent drought is a modification of the vegetation cover and biomass. The aim of our research is to investigate and monitor the evolution of this phenom- enon in Sicily using remote sensing techniques. To do this, a data set of NOAA-AVHRR multispectral images, acquired monthly from 1988 to 2005, has been calibrated and processed. A time series analysis (TSA) has been applied both on the NDVI and precipitation data sets in order to study the main characteristics of vegetation distribution during the period under investigation and to compare the vegeta…
SMOS-IC: An Alternative SMOS Soil Moisture and Vegetation Optical Depth Product
2017
© 2017 by the authors. The main goal of the Soil Moisture and Ocean Salinity (SMOS) mission over land surfaces is the production of global maps of soil moisture (SM) and vegetation optical depth (τ) based on multi-angular brightness temperature (TB) measurements at L-band. The operational SMOS Level 2 and Level 3 soil moisture algorithms account for different surface effects, such as vegetation opacity and soil roughness at 4 km resolution, in order to produce global retrievals of SM and τ. In this study, we present an alternative SMOS product that was developed by INRA (Institut National de la Recherche Agronomique) and CESBIO (Centre d'Etudes Spatiales de la BIOsphère). One of the main go…