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Neural network estimation of LAI, fAPAR, fCover and LAI*Cab, from top of canopy MERIS reflectance data: principles and validation / Cédric Bacour in Remote sensing of environment, vol 105 n° 4 (30/12/2006)  

Public [article]  inRemote sensing of environment > vol 105 n° 4 (30/12/2006) . - pp 313 - 325 Titre : Neural network estimation of LAI, fAPAR, fCover and LAI*Cab, from top of canopy MERIS reflectance data: principles and validation Type de document : Article/Communication Auteurs : Cédric Bacour, Auteur ; F. Baret, Auteur ; D. Beal, Auteur ; M. Weiss, Auteur ; K. Pavageau, Auteur Année de publication : 2006 Article en page(s) : pp 313 - 325 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image [Termes IGN] analyse comparative [Termes IGN] canopée [Termes IGN] chlorophylle [Termes IGN] classification par réseau neuronal [Termes IGN] image Envisat-MERIS [Termes IGN] Leaf Area Index [Termes IGN] modèle de transfert radiatif [Termes IGN] réflectance végétale Résumé : (Auteur) A neural network is developed to operationally estimate biophysical variables over land surfaces from the observations of the ENVISAT-MERIS instrument: the leaf area index (LAI), the fraction of absorbed photosynthetically active radiation (fAPAR), the fraction of vegetation cover (fCover), and the canopy chlorophyll content (LAI*Cab). The neural network requires as input the geometry of observation and the top of canopy reflectances, corrected from the atmospheric effects, in eleven spectral bands. It is trained on a reflectance database made of radiative transfer model simulations. The principles underlying the generation of the database and the design of the network are first presented. The estimated variables are then compared to other existing products, LAI- and fAPAR-MODIS and MGVI-MERIS, and validated against ground measurements performed in the framework of the VALERI project. Results show remarkable consistency of the temporal dynamics between the several products with however some differences in the range of variation. When compared to actual VALERI ground measurements, the proposed algorithm shows the best performances for LAI (RMSE = 0.47) and fAPAR (RMSE = 0.09). Copyright Elsevier Numéro de notice : A2006-562 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2006.07.014 En ligne : https://doi.org/10.1016/j.rse.2006.07.014 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28285 [article]

Quantifying spatial heterogeneity at the landscape scale using variogram models / S. Garrigues in Remote sensing of environment, vol 103 n° 1 (15 July 2006)  

Public [article]  inRemote sensing of environment > vol 103 n° 1 (15 July 2006) . - pp 81 - 96 Titre : Quantifying spatial heterogeneity at the landscape scale using variogram models Type de document : Article/Communication Auteurs : S. Garrigues, Auteur ; Denis Allard, Auteur ; F. Baret, Auteur ; M. Weiss, Auteur Année de publication : 2006 Article en page(s) : pp 81 - 96 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image [Termes IGN] couvert végétal [Termes IGN] erreur systématique [Termes IGN] hétérogénéité spatiale [Termes IGN] image à basse résolution [Termes IGN] Normalized Difference Vegetation Index [Termes IGN] pixel [Termes IGN] utilisation du sol [Termes IGN] variogramme Résumé : (Auteur) The monitoring of earth surface dynamic processes at a global scale requires high temporal frequency remote sensing observations which are provided up to now by moderate spatial resolution sensors. However, the spatial heterogeneity within the moderate spatial resolution pixel biases non-linear estimation processes of land surface variables from remote sensing data. To limit its influence on the description of land surface processes, corrections based on the quantification of the intra-pixel heterogeneity may be applied to non-linear estimation processes. A complementary strategy is to define the proper pixel size to capture the spatial variability of the data and minimize the intra-pixel variability. This work provides a methodology to characterize and quantify the spatial heterogeneity of landscape vegetation cover from the modeling of the variogram of high spatial resolution NDVI data. NDVI variograms for 18 landscapes extracted from the VALERI database show that the land use is the main factor of spatial variability as quantified by the variogram sill. Crop sites are more heterogeneous than natural vegetation and forest sites at the landscape level. The integral range summarizes all structural parameters of the variogram into a single characteristic area. Its square root quantifies the mean length scale (i.e. spatial scale) of the data, which varies between 216 and 1060 m over the 18 landscapes considered. The integral range is also used as a yardstick to judge if the size of an image is large enough to measure properly the length scales of the data with the variogram. We propose that it must be smaller than 5% of the image surface. The theoretical dispersion variance, computed from the variogram model, quantifies the spatial heterogeneity within a moderate resolution pixel. It increases rapidly with pixel size until this size is larger than the mean length scale of the data. Finally based on the analysis of 18 landscapes, the sufficient pixel size to capture the major part of the spatial variability of the vegetation cover at the landscape scale is estimated to be less than 100 m. Since for all the heterogeneous landscapes the loss of NDVI spatial variability was small at this spatial resolution, the bias generated by the intra-pixel spatial heterogeneity on non-linear estimation processes will be reduced. Copyright Elsevier Numéro de notice : A2006-283 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2006.03.013 En ligne : https://doi.org/10.1016/j.rse.2006.03.013 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28010 [article]

Intercalibration of vegetation indices from different sensor systems / M.D. Steven in Remote sensing of environment, vol 88 n° 4 (30/12/2003)  

Public [article]  inRemote sensing of environment > vol 88 n° 4 (30/12/2003) . - pp 412 - 422 Titre : Intercalibration of vegetation indices from different sensor systems Type de document : Article/Communication Auteurs : M.D. Steven, Auteur ; T.J. Malthus, Auteur ; F. Baret, Auteur ; H. Xu, Auteur ; M. Chopping, Auteur Année de publication : 2003 Article en page(s) : pp 412 - 422 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image [Termes IGN] données multicapteurs [Termes IGN] indice de végétation [Termes IGN] luminance lumineuse [Termes IGN] réflectance végétale [Termes IGN] simulation d'étalonnage Résumé : (Auteur) Spectroradiometric measurements were made over a range of crop canopy densities, soil backgrounds and foliage colour. The reflected spectral radiances were convoluted with the spectral response functions of a range of satellite instruments to simulate their responses. When Normalised Difference Vegetation Indices (NDVI) from the different instruments were compared, they varied by a few percent, but the values were strongly linearly related, allowing vegetation indices from one instrument to be intercalibrated against another. A table of conversion coefficents is presented for AVHRR, ATSR2, Landsat MSS, TM and ETM+, SPOT-2 and SPOT-4 HRV, IRS, IKONOS, SEAWIFS, MISR, MODIS, POLDER, Quickbird and MERIS (see Appendix A for glossary of acronyms). The same set of coefficients was found to apply, within the margin of error of the analysis, for the Soil Adjusted Vegetation Index SAVI. The relationships for SPOT vs. TM and for ATSR-2 vs. AVHRR were directly validated by comparison of atmospherically corrected image data. The results indicate that vegetation indices can be interconverted to a precision of 12%. This result offers improved opportunities for monitoring crops through the growing season and the prospects of better continuity of long-term monitoring of vegetation responses to environmental change. Numéro de notice : A2003-367 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2003.08.010 En ligne : https://doi.org/10.1016/j.rse.2003.08.010 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26447 [article]

A ratio vegetation index adjusted for soil brightness / D.J. Major in International Journal of Remote Sensing IJRS, vol 11 n° 5 (May 1990)  

Public [article]  inInternational Journal of Remote Sensing IJRS > vol 11 n° 5 (May 1990) . - pp 727 - 740 Titre : A ratio vegetation index adjusted for soil brightness Type de document : Article/Communication Auteurs : D.J. Major, Auteur ; F. Baret, Auteur ; Gérard Guyot, Auteur Année de publication : 1990 Article en page(s) : pp 727 - 740 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] couleur du sol [Termes IGN] humidité du sol [Termes IGN] indice de végétation [Termes IGN] luminance lumineuse [Termes IGN] rayonnement proche infrarouge [Termes IGN] réflectance du sol Résumé : (Auteur) Improved parameters for a soil-adjusted vegetation index (SAVI) are derived using SAIL model output for simulated wheat canopy reflectance. The SAVI is much less sensitive than the ratio vegetation index to changes in background caused by soil colour or surface soil moisture content. The parameters are developed to minimize variability due to soil brightness over the practical range of solar elevations, leaf angle distributions (LAD) and leaf area indices (LAI). The parameters are added to the near-infrared (NIR) and red reflectances before calculating the NIR/red ratio. Three new versions of the SAVI are developed based on the theoretical consideration of the effects of wet and dry soils. All three are superior to the NIR/red ratio, the perpendicular vegetation index and a soil-adjusted vegetation index. Our simplest version requires the addition of a parameter to the red reflectance. The second and third versions require an iterative procedure to find the best parameters that are then added to the red or the NIR and red reflectances. In general, SAVI adjustment parameters required to remove soil-brightness effects decrease as factors that obscure the soil-surface increase. Low solar elevation and high LAI result in increasingly negative values for the parameters. The NIR/red ratio is the vegetation index least influenced by soil brightness at LAI greater than three. Our iterated versions have lowest overall errors but are occasionally subject to higher errors at the combination of low zenith angles and erectophile canopies. The SAVI based on the bare soil reflectance performs best on field data. Numéro de notice : A1990-085 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/01431169008955053 En ligne : https://doi.org/10.1080/01431169008955053 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=25502 [article]

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080-90051	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Crop biomass evaluation using radiometric measurements / F. Baret in Photogrammetria, vol 43 n° 5 (June 1989)

Public [article]  inPhotogrammetria > vol 43 n° 5 (June 1989) . - pp 241 - 256 Titre : Crop biomass evaluation using radiometric measurements Type de document : Article/Communication Auteurs : F. Baret, Auteur ; D.J. Major, Auteur ; Gérard Guyot, Auteur Année de publication : 1989 Article en page(s) : pp 241 - 256 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] absorption [Termes IGN] cultures [Termes IGN] indice de végétation [Termes IGN] masse végétale [Termes IGN] valeur radiométrique Numéro de notice : A1989-182 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=25142 [article]

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Code-barres	Cote	Support	Localisation	Section	Disponibilité
081-89021	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Complementarity of middle-infrared with visible and near-infrared reflectance for monitoring wheat canopies / F. Baret in Remote sensing of environment, vol 26 n° 3 (01/12/1988)  

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Monitoring wheat canopies with a high spectral resolution radiometer / F. Baret in Remote sensing of environment, vol 22 n° 3 (01/08/1987)  

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Procedures for the description of agricultural crops and soils in optical and microwave remote sensing studies / J. Cihlar in International Journal of Remote Sensing IJRS, vol 8 n° 3 (March 1987)  

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Contribution au suivi radiométrique de cultures de céréales / F. Baret (1986)

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