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Application of 3D triangulations of airborne laser scanning data to estimate boreal forest leaf area index / Titta Majasalmi in International journal of applied Earth observation and geoinformation, vol 59 (July 2017)  

Public [article]  inInternational journal of applied Earth observation and geoinformation > vol 59 (July 2017) . - pp 53 - 62 Titre : Application of 3D triangulations of airborne laser scanning data to estimate boreal forest leaf area index Type de document : Article/Communication Auteurs : Titta Majasalmi, Auteur ; Lauri Korhonen, Auteur ; Ilkka Korpela, Auteur ; Jari Vauhkonen, Auteur Année de publication : 2017 Article en page(s) : pp 53 - 62 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] canopée [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] houppier [Termes IGN] Leaf Area Index [Termes IGN] modèle numérique de surface de la canopée [Termes IGN] Triangulated Irregular Network [Termes IGN] volume (grandeur) Numéro de notice : A2017-365 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.jag.2017.02.022 En ligne : https://doi.org/10.1016/j.jag.2017.02.022 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85792 [article]

Backscattering of individual LiDAR pulses from forest canopies explained by photogrammetrically derived vegetation structure / Ilkka Korpela in ISPRS Journal of photogrammetry and remote sensing, vol 83 (September 2013)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 83 (September 2013) . - pp 81 - 93 Titre : Backscattering of individual LiDAR pulses from forest canopies explained by photogrammetrically derived vegetation structure Type de document : Article/Communication Auteurs : Ilkka Korpela, Auteur ; Aarne Hovi, Auteur ; Lauri Korhonen, Auteur Année de publication : 2013 Article en page(s) : pp 81 - 93 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] appariement de lignes [Termes IGN] canopée [Termes IGN] diffusion du rayonnement [Termes IGN] forêt [Termes IGN] impulsion laser [Termes IGN] photogrammétrie métrologique [Termes IGN] photogrammétrie terrestre [Termes IGN] rétrodiffusion [Termes IGN] signal lidar Résumé : (Auteur) In recent years, airborne LiDAR sensors have shown remarkable performance in the mapping of forest vegetation. This experimental study looks at LiDAR data at the scale of individual pulses to elucidate the sources behind interpulse variation in backscattering. Close-range photogrammetry was used for obtaining the canopy reference measurements at the ratio scale. The experiments illustrated different orientation techniques in the field, LiDAR acquisitions and photogrammetry in both leaf-on and leaf-off conditions, and two-waveform recording LiDAR sensors. The intrafootprint branch silhouettes in zenith-looking images, in which the camera, footprint, and LiDAR sensor were collinear, were extracted and contrasted with LiDAR backscattering. An enhanced planimetric match (refinement of strip matching) was achieved by shifting the pulses in a strip and searching for the maximal correlation between the silhouette and LiDAR intensity. The relative silhouette explained up to 80–90% of the interpulse variation. We tested whether accounting for the Gaussian spread of intrafootprint irradiance would improve the correlations, but the effect was blurred by small-scale geometric noise. Accounting for receiver gain variations in the Leica ALS60 sensor data strengthened the dependences. The size of the vegetation objects required for triggering a LiDAR observation was analyzed. We demonstrated the use of LiDAR pulses adjacent to canopy vegetation, which did not trigger a canopy echo, for canopy mapping. Pulses not triggering an echo constitute the complement to the actual canopy. We conclude that field photogrammetry is a useful tool for mapping forest canopies from below and that quantitative analysis is feasible even at the scale of single pulses for enhanced understanding of LiDAR observations from vegetation. Numéro de notice : A2013-489 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2013.06.002 En ligne : https://doi.org/10.1016/j.isprsjprs.2013.06.002 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32627 [article]

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Range and AGC normalization in airborne discrete-return LiDAR intensity data for forest canopies / Ilkka Korpela in ISPRS Journal of photogrammetry and remote sensing, vol 65 n° 4 (July - August 2010)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 65 n° 4 (July - August 2010) . - pp 369 - 379 Titre : Range and AGC normalization in airborne discrete-return LiDAR intensity data for forest canopies Type de document : Article/Communication Auteurs : Ilkka Korpela, Auteur ; Hans Ole Ørka, Auteur ; Juha Hyyppä, Auteur ; et al., Auteur Année de publication : 2010 Article en page(s) : pp 369 - 379 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] couvert forestier [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] espèce végétale [Termes IGN] Finlande [Termes IGN] forêt boréale [Termes IGN] lasergrammétrie [Termes IGN] Pinophyta [Termes IGN] précision de la classification [Termes IGN] signal laser Résumé : (Auteur) Recently, the intensity characteristics of discrete-return LiDAR sensors were studied for vegetation classification. We examined two normalization procedures affecting LiDAR intensity through the scanning geometry and the system settings, namely, range normalization and the effects of the automatic gain control (AGC) in the Optech ALTM3100 and Leica ALS50-II sensors. Range normalization corresponds to weighting of the observed intensities with the term (R/RRef)a , where R is the range, RRef is a mean reference range, and aset membership, variant[2,4] is the exponent that is, according to theory, dependent on the target geometry. LiDAR points belonging to individual tree crowns were extracted for 13 887 trees in southern Finland. The coefficient of variation (CV) of the intensity was analyzed for a range of values of exponent a. The tree species classification performance using 13 intensity variables was also used for sensitivity analysis of the effect of a. The results were in line with the established theory, since the optimal level of a was lower (a~2) for trees with large or clumped leaves and higher (a~3) for diffuse coniferous crowns. Different echo groups also showed varying responses. Single-return pulses that represented strong reflections had a lower optimal value of a than the first and all echoes in a pulse. The gain in classification accuracy from the optimal selection of the exponent was 2%–3%, and the optimum for classification was different from that obtained using the CV analysis. In the ALS50-II sensor, the combined and optimized AGC and R normalizations had a notably larger effect (6%–9%) on classification accuracy. Our study demonstrates the ambiguity of R normalization in vegetation canopies. Numéro de notice : A2010-297 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2010.04.003 En ligne : https://doi.org/10.1016/j.isprsjprs.2010.04.003 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30491 [article]

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