The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Ismael Moya - One of the best experts on this subject based on the ideXlab platform.
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effect of Canopy Structure on sun induced chlorophyll fluorescence
Isprs Journal of Photogrammetry and Remote Sensing, 2012Co-Authors: Antoine Fournier, Yves Goulas, F Daumard, S Champagne, A Ounis, Ismael MoyaAbstract:Abstract We investigated the impact of Canopy Structure on chlorophyll fluorescence properties. For this purpose, we developed SpectroFLEX, an instrument for quantitative measurements of Canopy fluorescence in O2A and O2B atmospheric absorption bands. The fluorescence emission of a natural grass Canopy was compared with the leaf level fluorescence spectrum acquired simultaneously. It was found that the red-to-far-red fluorescence ratio decreased by a factor of two from the leaf to the Canopy level. In addition, this ratio decreased under high light conditions. FluoSAIL simulations were conducted to study the impact of Canopy density and geometry on this decrease. This effect has been attributed to a preferential re-absorption of red fluorescence emission during radiative transfer within the Canopy compared to far-red emission.
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Effect of Canopy Structure on sun-induced chlorophyll fluorescence
ISPRS Journal of Photogrammetry and Remote Sensing, 2012Co-Authors: Antoine Fournier, Yves Goulas, F Daumard, S Champagne, A Ounis, Ismael MoyaAbstract:We investigated the impact of Canopy Structure on chlorophyll fluorescence properties. For this purpose, we developed SpectroFLEX, an instrument for quantitative measurements of Canopy fluorescence in O 2A and O 2B atmospheric absorption bands. The fluorescence emission of a natural grass Canopy was compared with the leaf level fluorescence spectrum acquired simultaneously. It was found that the red-to-far-red fluorescence ratio decreased by a factor of two from the leaf to the Canopy level. In addition, this ratio decreased under high light conditions. FluoSAIL simulations were conducted to study the impact of Canopy density and geometry on this decrease. This effect has been attributed to a preferential re-absorption of red fluorescence emission during radiative transfer within the Canopy compared to far-red emission. © 2012 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).
Felix Morsdorf - One of the best experts on this subject based on the ideXlab platform.
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forest Canopy Structure characterization a data driven approach
Forest Ecology and Management, 2015Co-Authors: Reik Leiterer, Reinhard Furrer, Michael E. Schaepman, Felix MorsdorfAbstract:Forest Canopy Structure influences and partitions the energy fluxes between the atmosphere and vegetation. It serves as an indicator of a variety of biophysical variables and ecosystem goods and services. Airborne laser scanning (ALS) can simultaneously provide horizontal and vertical information on Canopy Structure. Existing approaches to assess Canopy Structure often focus on in situ collected structural variables and require a substantial set of prior information about stand characteristics. They also rely on pre-defined spatial units and are usually dependent on site-specific model calibrations. We propose a method to provide quantitative Canopy-Structure descriptors on different scales, retrieved from ALS data. The approach includes (i) a sensitivity assessment and a quantification of ALS-derived Canopy-Structure information dependent on ALS data properties, (ii) an automatic determination of the most feasible spatial unit for Canopy-Structure characterization, and (iii) the derivation of Canopy-Structure types (CSTs) using a hierarchical, multi-scale classification approach based on Bayesian robust mixture models (BRMM), satisfying structurally homogenous criteria without the use of in situ calibration information. The CSTs resulted in retrievals of Canopy layering (single-, two-, and multi-layered canopies) and Canopy types (deciduous or evergreen canopies). Retrievals classified seven CSTs with accuracies ranging from 52% to 82% user accuracy (Canopy layering) and 89–99% user accuracy (Canopy type). The method supports a data-driven approach, allowing for an efficient monitoring of Canopy Structure.
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Retrieval of Canopy Structure types for forest characterization using multi-temporal airborne laser scanning
2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2015Co-Authors: Reik Leiterer, Reinhard Furrer, Michael E. Schaepman, Felix MorsdorfAbstract:We present a method to characterize forest Canopy Structure in space and time based on vertical echo distributions from airborne laser scanning (ALS). We developed a transferable, grid-based method using ALS data combined with an automatic determination of the best feasible spatial unit for Canopy Structure characterization. We derive Canopy Structure types (CSTs) using a hierarchical, multi-scale classification approach based on Bayesian robust mixture models (BRMMs), which satisfy structurally homogenous criteria without the use of in-situ calibration information. The validation shows promising results for the CSTs, particularly in terms of seasonal and horizontal variations in vertical Canopy Structure. We conclude that our method can improve the robustness and reliability of Canopy Structure characterization. Future work will include tests of transferability to a larger variety of forests and extensive testing using CSTs as a structural classification scheme.
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IGARSS - Retrieval of Canopy Structure types for forest characterization using multi-temporal airborne laser scanning
2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2015Co-Authors: Reik Leiterer, Reinhard Furrer, Michael E. Schaepman, Felix MorsdorfAbstract:We present a method to characterize forest Canopy Structure in space and time based on vertical echo distributions from airborne laser scanning (ALS). We developed a transferable, grid-based method using ALS data combined with an automatic determination of the best feasible spatial unit for Canopy Structure characterization. We derive Canopy Structure types (CSTs) using a hierarchical, multi-scale classification approach based on Bayesian robust mixture models (BRMMs), which satisfy structurally homogenous criteria without the use of in-situ calibration information. The validation shows promising results for the CSTs, particularly in terms of seasonal and horizontal variations in vertical Canopy Structure. We conclude that our method can improve the robustness and reliability of Canopy Structure characterization. Future work will include tests of transferability to a larger variety of forests and extensive testing using CSTs as a structural classification scheme.
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Robust characterization of forest Canopy Structure using Bayesian mixture models
2014Co-Authors: Reik Leiterer, Reinhard Furrer, Felix Morsdorf, Michael E. SchaepmanAbstract:Airborne laser scanning (ALS) systems are suitable to provide not only horizontal information on the forest Canopy Structure, but also vertical information based on the Canopy penetration of the emitted signal. Existing approaches for forest Canopy Structure characterization often include pre-defined analysis set up (e.g. determination of the spatial scales) and manual processing steps. They are in need of additional information on stand characteristics for the calculation of bio-physical variables and/or have specific requirements for the ALS data. Therefore, the transferability of methods on differing Canopy Structures types is usually limited and results will hardly be inter-comparable. We developed a robust, multi-scale assessment of forest Structure patterns at Canopy level to derive homogeneous Canopy Structure types (CSTs). CSTs represent a unique set of horizontal and vertical forest Canopy structural variables. For their development, we followed three main objectives: i) investigation of the sensitivity of ALS derived forest Structure information to data properties such as echo density, scan angle, and acquisition date; ii) analysis of the consequence of using pre-defined grid cell sizes for forest Structure characterization and the development of an automatic method to derive suitable grid cell size for vertical Canopy Structure analyses; and iii) robust stratification of the forest Canopy in various discrete layers based on the most suitable spatial scales and derivation of the CSTs as well as their spatial distribution using a hierarchical, multi-scale classification approach based on Bayesian robust mixture models. Our method supports and improves operational forest Structure monitoring, allowing for a comprehensive assessment of the inter-annual variability of derived Canopy Structure information, and provides a tool for scale-independent cross-comparisons to results of other ALS based Canopy Structure analysis. In particular, in cases where sound thematic definitions, from e.g. the forest inventory, are missing, our approach demonstrated to be successful in determining the most suitable vertical and horizontal scales for forest Structure analyses. These findings are an important step towards operational, ALS based forest Structure monitoring and changes thereof, which are often subject to different acquisition dates and therefore inconsistent acquisition conditions.
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A voxel-based approach for Canopy Structure characterization using full-waveform airborne laser scanning
2012 IEEE International Geoscience and Remote Sensing Symposium, 2012Co-Authors: Reik Leiterer, Michael E. Schaepman, Felix Morsdorf, H. Torabzadeh, W. Mücke, N. Pfeifer, M. HollausAbstract:Forests play a significant role in the global biogeochemical and -physical cycles and particularly the complex three-dimensional forest Canopy Structure influences the fluxes of energy and matter between the atmosphere and forests. Assessing this Structure quantitatively using conventional fieldwork or traditional remote sensing methods is difficult, whereas airborne laser scanning (ALS) systems have proven to be suitable for providing explicit vertical information for large areas. However, most existing ALS based approaches include manual processing steps or need additional data about stand characteristics. To solve these issues, a robust and automatic multi-dimensional clustering method was developed to derive forest Canopy Structure types (CSTs) based on full-waveform ALS data. The results show that it is possible to develop an automatic, self-sustained and transferable method for: the extraction of CSTs without any previous knowledge about the forest stand; and the extraction of bio-physical parameters based on the resulting CSTs.
Yun Bian - One of the best experts on this subject based on the ideXlab platform.
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Laser scanning based three dimensional measurement of vegetation Canopy Structure
Optics and Lasers in Engineering, 2014Co-Authors: Xudong Li, Hongzhi Jiang, Huijie Zhao, Yun BianAbstract:Abstract Three-dimensional vegetation Canopy Structure is the critical original data source for the evaluation of radiation transfer modeling, remote sensing products validation and many other remote sensing applications. Although a number of three-dimensional measurement techniques have been already used in industrial measurement, few of them can be directly applied to vegetation Canopy Structure measurement because of the insufficient ability of non-contact and field measurement, as well as the possibility of matching with other information like vegetation spectra. In this paper, a non-contact laser scanning based three-dimensional measurement system is proposed to acquire the Structure of the vegetation Canopy, which is based on the flying point scanning triangulation. It gives a way of obtaining dense Canopy Structure data in-situ without neither contacting nor sticking the targets on the vegetation. The system principle, modeling and novel calibration approach, which directly calibrates the equation of the incident laser beam and other key techniques related to the system implementation are presented and discussed in detail. The system's measurement ability is demonstrated by acquiring different shaped leaves. The scanning point separation and the accuracy of three-dimensional points are 3–5 mm and 1 mm respectively. The points can then be used to calculate the geometric descriptive parameters of the Canopy including plant area, leaf overlap, leaf area index, and gap fraction. It can also be used to establish highly detailed three-dimensional digital model of the vegetation Canopy.
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Laser scanning based three dimensional measurement of vegetation Canopy Structure
Optics and Lasers in Engineering, 2014Co-Authors: Xudong Li, Hongzhi Jiang, Huijie Zhao, Yun BianAbstract:Three-dimensional vegetation Canopy Structure is the critical original data source for the evaluation of radiation transfer modeling, remote sensing products validation and many other remote sensing applications. Although a number of three-dimensional measurement techniques have been already used in industrial measurement, few of them can be directly applied to vegetation Canopy Structure measurement because of the insufficient ability of non-contact and field measurement, as well as the possibility of matching with other information like vegetation spectra. In this paper, a non-contact laser scanning based three-dimensional measurement system is proposed to acquire the Structure of the vegetation Canopy, which is based on the flying point scanning triangulation. It gives a way of obtaining dense Canopy Structure data in-situ without neither contacting nor sticking the targets on the vegetation. The system principle, modeling and novel calibration approach, which directly calibrates the equation of the incident laser beam and other key techniques related to the system implementation are presented and discussed in detail. The system's measurement ability is demonstrated by acquiring different shaped leaves. The scanning point separation and the accuracy of three-dimensional points are 3-5 mm and 1 mm respectively. The points can then be used to calculate the geometric descriptive parameters of the Canopy including plant area, leaf overlap, leaf area index, and gap fraction. It can also be used to establish highly detailed three-dimensional digital model of the vegetation Canopy. © 2013 Elsevier Ltd.
V. Y. Ivanov - One of the best experts on this subject based on the ideXlab platform.
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Large eddy simulations of surface roughness parameter sensitivity to Canopy-Structure characteristics
Biogeosciences Discussions, 2014Co-Authors: K. D. Maurer, G. Bohrer, V. Y. IvanovAbstract:Abstract. Surface roughness parameters are at the core of every model representation of the coupling and interactions between land-surface and atmosphere, and are used in every model of surface fluxes. However, most models assume these parameters to be a fixed property of plant functional type and do not vary them in response to spatial or temporal changes to Canopy Structure. In part, this is due to the difficulty of reducing the complexity of Canopy Structure and its spatiotemporal dynamic and heterogeneity to less than a handful of parameters describing its effects of atmosphere–surface interactions. In this study we use large-eddy simulations to explore, in silico, the effects of Canopy Structure characteristics on surface roughness parameters. We performed a virtual experiment to test the sensitivity of resolved surface roughness to four axes of Canopy Structure: (1) leaf area index, (2) the vertical profile of leaf density, (3) Canopy height, and (4) Canopy gap fraction. We found roughness parameters to be highly variable, but were able to find positive relationships between displacement height and maximum Canopy height, aerodynamic Canopy height and maximum Canopy height and leaf area index, and eddy-penetration depth and gap fraction. We also found negative relationships between aerodynamic Canopy height and gap fraction, and between eddy-penetration depth and maximum Canopy height and leaf area index. Using a decade of wind and Canopy Structure observations in a site in Michigan, we tested the effectiveness of our model-resolved parameters in predicting the frictional velocity over heterogeneous and disturbed canopies. We compared it with three other semi-empirical models and with a decade of meteorological observations. We found that parameterizations with fixed representations of roughness performed relatively well. Nonetheless, some empirical approaches that incorporate seasonal and inter-annual changes to the Canopy Structure performed even better than models with temporally fixed parameters.
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large eddy simulations of surface roughness parameter sensitivity to Canopy Structure characteristics
Biogeosciences, 2014Co-Authors: K. D. Maurer, G. Bohrer, W Kenny, V. Y. IvanovAbstract:Abstract. Surface roughness parameters, namely the roughness length and displacement height, are an integral input used to model surface fluxes. However, most models assume these parameters to be a fixed property of plant functional type and disregard the governing structural heterogeneity and dynamics. In this study, we use large-eddy simulations to explore, in silico, the effects of Canopy-Structure characteristics on surface roughness parameters. We performed a virtual experiment to test the sensitivity of resolved surface roughness to four axes of Canopy Structure: (1) leaf area index, (2) the vertical profile of leaf density, (3) Canopy height, and (4) Canopy gap fraction. We found roughness parameters to be highly variable, but uncovered positive relationships between displacement height and maximum Canopy height, aerodynamic Canopy height and maximum Canopy height and leaf area index, and eddy-penetration depth and gap fraction. We also found negative relationships between aerodynamic Canopy height and gap fraction, as well as between eddy-penetration depth and maximum Canopy height and leaf area index. We generalized our model results into a virtual "biometric" parameterization that relates roughness length and displacement height to Canopy height, leaf area index, and gap fraction. Using a decade of wind and Canopy-Structure observations in a site in Michigan, we tested the effectiveness of our model-driven biometric parameterization approach in predicting the friction velocity over heterogeneous and disturbed canopies. We compared the accuracy of these predictions with the friction-velocity predictions obtained from the common simple approximation related to Canopy height, the values calculated with large-eddy simulations of the explicit Canopy Structure as measured by airborne and ground-based lidar, two other parameterization approaches that utilize varying Canopy-Structure inputs, and the annual and decadal means of the surface roughness parameters at the site from meteorological observations. We found that the classical representation of constant roughness parameters (in space and time) as a fraction of Canopy height performed relatively well. Nonetheless, of the approaches we tested, most of the empirical approaches that incorporate seasonal and interannual variation of roughness length and displacement height as a function of the dynamics of Canopy Structure produced more precise and less biased estimates for friction velocity than models with temporally invariable parameters.
Antoine Fournier - One of the best experts on this subject based on the ideXlab platform.
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effect of Canopy Structure on sun induced chlorophyll fluorescence
Isprs Journal of Photogrammetry and Remote Sensing, 2012Co-Authors: Antoine Fournier, Yves Goulas, F Daumard, S Champagne, A Ounis, Ismael MoyaAbstract:Abstract We investigated the impact of Canopy Structure on chlorophyll fluorescence properties. For this purpose, we developed SpectroFLEX, an instrument for quantitative measurements of Canopy fluorescence in O2A and O2B atmospheric absorption bands. The fluorescence emission of a natural grass Canopy was compared with the leaf level fluorescence spectrum acquired simultaneously. It was found that the red-to-far-red fluorescence ratio decreased by a factor of two from the leaf to the Canopy level. In addition, this ratio decreased under high light conditions. FluoSAIL simulations were conducted to study the impact of Canopy density and geometry on this decrease. This effect has been attributed to a preferential re-absorption of red fluorescence emission during radiative transfer within the Canopy compared to far-red emission.
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Effect of Canopy Structure on sun-induced chlorophyll fluorescence
ISPRS Journal of Photogrammetry and Remote Sensing, 2012Co-Authors: Antoine Fournier, Yves Goulas, F Daumard, S Champagne, A Ounis, Ismael MoyaAbstract:We investigated the impact of Canopy Structure on chlorophyll fluorescence properties. For this purpose, we developed SpectroFLEX, an instrument for quantitative measurements of Canopy fluorescence in O 2A and O 2B atmospheric absorption bands. The fluorescence emission of a natural grass Canopy was compared with the leaf level fluorescence spectrum acquired simultaneously. It was found that the red-to-far-red fluorescence ratio decreased by a factor of two from the leaf to the Canopy level. In addition, this ratio decreased under high light conditions. FluoSAIL simulations were conducted to study the impact of Canopy density and geometry on this decrease. This effect has been attributed to a preferential re-absorption of red fluorescence emission during radiative transfer within the Canopy compared to far-red emission. © 2012 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).