J. Gastellu-etchegorry - Profile on Academia.edu (original) (raw)

Papers by J. Gastellu-etchegorry

Remote Sensing of Environment, 2008

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Agricultural and Forest Meteorology, 2009

Remote Sensing for Agriculture, Ecosystems, and Hydrology XII, 2010

Tropical forests are complex ecosystems where the potential of remote sensing has not yet been fu... more Tropical forests are complex ecosystems where the potential of remote sensing has not yet been fully realized. The increasing availability of satellite metric imagery along with canopy altimetry from airborne LiDAR open new prospects to detect individual trees. For this objective, we optimized, calibrated and applied a model based on marked point processes to detect trees in high biomass mangroves of French Guiana by considering a set of 1m pixel images including 1) panchromatic images from the IKONOS sensor 2) LiDAR-derived canopy 2D altimetry and 3) reflectance panchromatic images simulated by the DART-model. The relevance of detection is then discussed considering: (i) the agreement in space of detected crown centers locations with known true locations for the DART images and also the detection agreement for each pair of IKONOS and LiDAR images, and (ii) the comparison between the frequency distributions of the diameters of the detected crowns and of the tree trunks measured in the field. Both distributions are expected to be related due to the allometry relationships between trunk and crown. Results are encouraging provided that crown sizes sufficiently large compared to 1m pixels.

BRDF behaviour of a tropical forest surveyed from space

IGARSS'97. 1997 IEEE International Geoscience and Remote Sensing Symposium Proceedings. Remote Sensing - A Scientific Vision for Sustainable Development

Survey of tropical forest evolution and functioning with remote sensing is hampered by the variab... more Survey of tropical forest evolution and functioning with remote sensing is hampered by the variability of their BRDF (bi-directional reflectance distribution function); e.g. automatic classifications may be totally erroneous if view and illumination conditions are not taken into account. The authors used a new radiative transfer model (DART, Discrete Anisotropic Radiative Transfer) to analyze BRDF behaviour of a tropical forest

Journal of Geophysical Research, 2004

The Radiation Transfer Model Intercomparison (RAMI) initiative is a communitydriven exercise to b... more The Radiation Transfer Model Intercomparison (RAMI) initiative is a communitydriven exercise to benchmark the models of radiation transfer (RT) used to represent the reflectance of terrestrial surfaces. Systematic model intercomparisons started in 1999 as a self-organized, open-access, voluntary activity of the RT modeling community. The results of the first phase were published by . The present paper describes the benchmarking protocol and the results achieved during the second phase, which took place during 2002. This second phase included two major components: The first one included a rerun of all direct-mode tests proposed during the first phase, to accommodate the evaluation of models that have been upgraded since, and the participation of new models into the entire exercise. The second component was designed to probe the performance of three-dimensional models in complex heterogeneous environments, which closely mimic the observations of actual space instruments operating at various spatial resolutions over forest canopy systems. Phases 1 and 2 of RAMI both confirm not only that a majority of the radiation transfer models participating in RAMI are in good agreement between themselves for relatively simple radiation transfer problems but also that these models exhibit significant discrepancies when considering more complex but nevertheless realistic geophysical scenarios. Specific recommendations are provided to guide the future of this benchmarking program (Phase 3 and beyond).

Remote Sensing of Environment, 1996

The DART (discrete anisotropic radiative transfer) model simulates radiative transfer in heteroge... more The DART (discrete anisotropic radiative transfer) model simulates radiative transfer in heterogeneous 3-D scenes that may comprise different landscape features; i.e., leaves, grass, trunks, water, soil. The scene is divided into a rectangular cell matrix, i.e., building block for simulating larger scenes. Cells are parallelipipedic. Their optical properties are represented by individual scattering phase functions that are directly input into the model or are computed with optical and structural characteristics of elements within the cell. Radiation scattering and propagation are simulated with the exact kernel and discrete ordinate approaches; any set of discrete direction can be selected. In addition to topography and hot spot, leaf specular and first-order polarization mechanisms are modeled. Two major iterative steps are distinguished: 1) Cell illumination with direct sun radiation: Within cell multiple scattering is accurately simulated. 2) Interception and scattering of previously scattered radiation: Atmospheric radiation, possibly anisotropic, is input at this stage. Multiple scattering is stored as spherical harmonics expansions, for reducing computer memory constraints. The model iterates on step 2, for all cells, and stops with the energetic equilibrium. Two simple accelerating techniques can be used: 1) Gauss Seidel method, i.e., simulation of scattering with radiation already scattered at the iteration stage, and (2) decrease of the spherical harmonics expansion order with the iteration order. Moreover, convergence towards the energetic equilibrium is accelerated with an exponential fitting technique. This model predicts the bidirectional reflectance distribution function of 3-19 canopies. Radiation components associated with leaf volume and surface mechanisms are distin

Radar Remote Sensing For Vegetation With Special Reference To Nipah Delineation On Sir-A Image

Indonesian Journal of Geography, 1987

European Journal of Remote Sensing

The derivation of the radiative budget of urban environments has gained a high interest in the re... more The derivation of the radiative budget of urban environments has gained a high interest in the recent years as an essential part of the global energy budget of big cities. Urban 3D (three-dimensional) heterogeneity hampers its assessment with in-situ measurements, which stresses the interest of Earth Observation (EO) satellites. Improvements in remote-sensing technology and 3D urban databases open the way to new deterministic approaches. This paper presents a new method that derives maps of urban shortwave exitance, albedo and radiative budget Q SW * from EO satellite images (e.g. Sentinel 2, Landsat-8), using the discrete anisotropic radiative transfer model. In a preliminary step, it derives maps of urban material optical properties from an EO satellite image, at the spatial resolution of this EO image. The method is applied to the city of Basel, Switzerland, in the frame of the European Community H2020 URBANFLUXES (www.urbanfluxes.eu) project which aims at improving our knowledge on anthropogenic heat fluxes in European cities. Results are very encouraging. Indeed, urban Q SW * derived from 234 EO satellite images, ranging from 200 to 800 W/m 2 through the year, is very close to in-situ measured Q SW *: ≈15 W/m 2 temporal root mean square error (i.e. 2.7% mean relative difference) relative to measurements.

Forests

Advances in high-performance computer resources and exploitation of high-density terrestrial lase... more Advances in high-performance computer resources and exploitation of high-density terrestrial laser scanning (TLS) data allow for reconstruction of close-to-reality 3D forest scenes for use in canopy radiative transfer models. Consequently, our main objectives were (i) to reconstruct 3D representation of Norway spruce (Picea abies) trees by deriving distribution of woody and foliage elements from TLS and field structure data and (ii) to use the reconstructed 3D spruce representations for evaluation of the effects of canopy structure on forest reflectance simulated in the Discrete Anisotropic Radiative Transfer (DART) model. Data for this study were combined from two spruce research sites located in the mountainous areas of the Czech Republic. The canopy structure effects on simulated top-of-canopy reflectance were evaluated for four scenarios (10 × 10 m scenes with 10 trees), ranging from geometrically simple to highly detailed architectures. First scenario A used predefined simple t...

Remote Sensing of Environment

If citing, it is advised that you check and use the publisher's definitive version for pagination... more If citing, it is advised that you check and use the publisher's definitive version for pagination, volume/issue, and date of publication details. And where the final published version is provided on the Research Portal, if citing you are again advised to check the publisher's website for any subsequent corrections.

Biogeosciences, 2016

The complex three-dimensional (3-D) structure of tropical forests generates a diversity of light ... more The complex three-dimensional (3-D) structure of tropical forests generates a diversity of light environments for canopy and understory trees. Understanding diurnal and seasonal changes in light availability is critical for interpreting measurements of net ecosystem exchange and improving ecosystem models. Here, we used the Discrete Anisotropic Radiative Transfer (DART) model to simulate leaf absorption of photosynthetically active radiation (lAPAR) for an Amazon forest. The 3-D model scene was developed from airborne lidar data, and local measurements of leaf reflectance, aerosols, and PAR were used to model lAPAR under direct and diffuse illumination conditions. Simulated lAPAR under clear-sky and cloudy conditions was corrected for light saturation effects to estimate light utilization, the fraction of lAPAR available for photosynthesis. Although the fraction of incoming PAR absorbed by leaves was consist...

Simulation of the BRDF of forest cover with the coupling of high and medium resolution reflectance models

1995 International Geoscience and Remote Sensing Symposium, IGARSS '95. Quantitative Remote Sensing for Science and Applications, 1995

Information extraction from remote sensing data with the help of physical modeling requires an ap... more Information extraction from remote sensing data with the help of physical modeling requires an approach that retains the 3D complexity of covers while dealing with a limited data volume, i.e. the scene is made of a small number of complex elements. Therefore, the authors developed a methodology that couples a high and a medium reflectance models: output (i.e. mean transmittance

Remote sensing spectrometry of a temperate deciduous forest-a modeling approach

IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium, 1996

This work evaluates the potential of remote sensing visible and near infrared spectrometry for st... more This work evaluates the potential of remote sensing visible and near infrared spectrometry for studying the dynamics of a temperate deciduous forest. It is conducted with the airborne Reflective Optics Spectrometric Imaging System (ROSIS) in the frame of the European Multisensors Airborne Campaign (EMAC-94). A modeling approach, i.e. coupled canopy and leaf reflectance models, is used for assessing the sensitivity

Impact of surface heterogeneity on temperature, mass and energy exchanges

IGARSS 2003. 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477), 2003

In an attempt to provide more accurate estimates of sensible and latent heat fluxes and surface t... more In an attempt to provide more accurate estimates of sensible and latent heat fluxes and surface temperature, a 3- dimensional model is being developed. The originality of this model is to rely on a realistic description of the studied landscape: architecture, temperature, optical properties. It combines 3 components: (1) a radiative component managed by the 3-D radiative transfer DART model

Retrieval of forest biophysical parameters from remote sensing images with the DART model

IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium, 1996

This paper presents a quantitative analysis of the sensitivity of textural information of high re... more This paper presents a quantitative analysis of the sensitivity of textural information of high resolution remote sensing images of a forest plantation (Les Landes, France) with a number of biophysical characteristics: tree cover, crown diameter, distance between rows and leaf area index (LAI). The influence of spatial resolution and viewing and illumination configurations are also assessed. The work is conducted

Tropical Vegetation Mappjng with Combined Visible and Sar Spaceborne Data

[Proceedings] IGARSS '92 International Geoscience and Remote Sensing Symposium, 1992

Under the tropics, due to high cloud cover, vegetation monitoring can only be achieved by using b... more Under the tropics, due to high cloud cover, vegetation monitoring can only be achieved by using both visible and microwave data. In the present study, SIR-B and SPOT data acquired over central Sumatra are used in a supervised classifrcation of vegetation. Assessment of SAR-data potentialities is carried on by using 1) SIR-B image alone, 2) combined SIR-B and SPOT data.

Computer Assisted with Spot Land Cover Mapping in Indonesia

12th Canadian Symposium on Remote Sensing Geoscience and Remote Sensing Symposium,, 1989

A Modeling Approach for Studying Forest Chlorophyll Content

Remote Sensing of Environment, 2000

Imaging spectroscopy from space is a potentially powerful tool for assessing vegetation chemistry... more Imaging spectroscopy from space is a potentially powerful tool for assessing vegetation chemistry with approaches that rely either on empirical relationships or on the inversion of reflectance models. However, this assessment can be erroneous if the 3-D spatial distribution of the vegetation is neglected. Sophisticated radiative transfer models are often required to account for the 3-D canopy architecture. Due to

Retrieval of Vegetation Biophysical Parameters with Aviris, Tms and Ism - the Landes, South West France

[Proceedings] IGARSS '92 International Geoscience and Remote Sensing Symposium, 1992

Abstract This paper evaluates state-of-the-art parametric and nonparametric approaches for the es... more Abstract This paper evaluates state-of-the-art parametric and nonparametric approaches for the estimation of leaf chlorophyll content (Chl)(Chl) (Chl), leaf area index, and fractional vegetation cover from space. The parametric approach involves comparison of established and ...

Revue Française d'Allergologie et d'Immunologie Clinique, 2002

La détection des champs comportant des populations denses d'ambroisie (Ambrosia artemisiifolia L.... more La détection des champs comportant des populations denses d'ambroisie (Ambrosia artemisiifolia L.) par des méthodes spatiales pourrait être possible. Cette détection qui conduirait à une cartographie des parcelles « infestées » constituerait une aide précieuse pour engager des campagnes de désherbage et apprécier l'évolution spatiotemporelle de la plante. Les difficultés méthodologiques liées à la détection d'une adventice concernent la mixité des peuplements, la petite surface des zones infestées et le risque de confusion du comportement spectral avec celui d'autres espèces. Un repérage sur le terrain de zones particulièrement infestées dans la région lyonnaise (Rhône) a eu lieu le 27 juillet 2001. Ces données de terrain ont été utilisées pour exploiter deux images ASTER 1B (satellite Terra) du 26 juin et du 13 août 2001 de la zone prospectée. Une mesure réalisée en laboratoire sur un échantillon prélevé sur le terrain a déterminé le spectre de réflectance. Les résultats sont les suivants : il existe des cas où le comportement spectral des parcelles abritant une forte densité d'ambroisie permet leur cartographie. Lorsque la densité de cette espèce diminue, les signatures spectrales des peuplements deviennent multiformes et exigent des études plus approfondies. Des progrès prochains peuvent être attendus de l'utilisation de capteurs à très haute résolution spatiale tel IKONOS (résolution de 1 m en panchromatique ou 4 m en multispectral) ou le futur SPOT 5 (résolution de 2 à 3 m en panchromatique ou 10 m en multispectral) qui permettent de travailler à des résolutions de l'ordre du mètre.