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Angular reflectance of leaves with a dual-wavelength terrestrial lidar and its implications for leaf-bark separation and leaf moisture estimation / Steven Hancock in IEEE Transactions on geoscience and remote sensing, vol 55 n° 6 (June 2017)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 55 n° 6 (June 2017) . - pp 3084 - 3090 Titre : Angular reflectance of leaves with a dual-wavelength terrestrial lidar and its implications for leaf-bark separation and leaf moisture estimation Type de document : Article/Communication Auteurs : Steven Hancock, Auteur ; Rachel Gaulton, Auteur ; F. Mark Danson, Auteur Année de publication : 2017 Article en page(s) : pp 3084 - 3090 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] angle d'incidence [Termes IGN] données lidar [Termes IGN] écorce [Termes IGN] indice de diversité [Termes IGN] longueur d'onde [Termes IGN] réflectance de surface [Termes IGN] réflectance végétale [Termes IGN] teneur en eau de la végétation Résumé : (Auteur) A new generation of multiwavelength lidars offers the potential to measure the structure and biochemistry of vegetation simultaneously, using range resolved spectral indices to overcome the confounding effects in passive optical measurements. However, the reflectance of leaves depends on the angle of incidence, and if this dependence varies between wavelengths, the resulting spectral indices will also vary with the angle of incidence, complicating their use in separating structural and biochemical effects in vegetation canopies. The Salford Advanced Laser Canopy Analyser (SALCA) dual-wavelength terrestrial laser scanner was used to measure the angular dependence of reflectance for a range of leaves at the wavelengths used by the new generation of multiwavelength lidars, 1063 and 1545 nm, as used by SALCA, DWEL, and the Optech Titan. The influence of the angle of incidence on the normalized difference index (NDI) of these wavelengths was also assessed. The reflectance at both wavelengths depended on the angle of incidence and could be well modelled as a cosine. The change in the NDI with the leaf angle of incidence was small compared with the observed difference in the NDI between fresh and dry leaves and between leaf and bark. Therefore, it is concluded that angular effects will not significantly impact leaf moisture retrievals or prevent leaf/bark separation for the wavelengths used in the new generation of 1063- and 1545-nm multiwavelength lidars. Numéro de notice : A2017-474 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2017.2652140 En ligne : http://dx.doi.org/10.1109/TGRS.2017.2652140 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=86399 [article]

Is waveform worth it? A comparison of LiDAR approaches for vegetation and landscape characterization / Karen Anderson in Remote sensing in ecology and conservation, vol 2 n° 1 (February 2016)  

Public [article]  inRemote sensing in ecology and conservation > vol 2 n° 1 (February 2016) . - pp 5 - 15 Titre : Is waveform worth it? A comparison of LiDAR approaches for vegetation and landscape characterization Type de document : Article/Communication Auteurs : Karen Anderson, Auteur ; Steven Hancock, Auteur ; Mathias I. Disney, Auteur ; Kevin J. Gaston, Auteur Année de publication : 2016 Article en page(s) : pp 5 - 15 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] canopée [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] forêt [Termes IGN] forme d'onde [Termes IGN] sous-bois [Termes IGN] sous-étage Résumé : (auteur) Light Detection and Ranging (LiDAR) systems are frequently used in ecological studies to measure vegetation canopy structure. Waveform LiDAR systems offer new capabilities for vegetation modelling by measuring the time-varying signal of the laser pulse as it illuminates different elements of the canopy, providing an opportunity to describe the 3D structure of vegetation canopies more fully. This article provides a comparison between waveform airborne laser scanning (ALS) data and discrete return ALS data, using terrestrial laser scanning (TLS) data as an independent validation. With reference to two urban landscape typologies, we demonstrate that discrete return ALS data provided more biased and less consistent measurements of woodland canopy height (in a 100% tree covered plot, height underestimation bias = 0.82 m; SD = 1.78 m) than waveform ALS data (height overestimation bias = 0.65 m; SD = 1.45 m). The same biases were found in suburban data (in a plot consisting of 100% hard targets e.g. roads and pavements), but discrete return ALS were more consistent here than waveform data (SD=0.57 m compared to waveform SD=0.76 m). Discrete return ALS data performed poorly in describing the canopy understorey, compared to waveform data. Our results also highlighted errors in discrete return ALS intensity, which were not present with waveform data. Waveform ALS data therefore offer an improved method for measuring the three-dimensional structure of vegetation systems, but carry a higher data processing cost. New toolkits for analysing waveform data will expedite future analysis and allow ecologists to exploit the information content of waveform LiDAR. Numéro de notice : A2016--166 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article DOI : 10.1002/rse2.8 En ligne : http://doi.org/10.1002/rse2.8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=87172 [article]