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Spherical harmonic synthesis of area-mean potential values on irregular surfaces / Blažej Bucha in Journal of geodesy, vol 96 n° 10 (October 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 10 (October 2022) . - n° 68 Titre : Spherical harmonic synthesis of area-mean potential values on irregular surfaces Type de document : Article/Communication Auteurs : Blažej Bucha, Auteur Année de publication : 2022 Article en page(s) : n° 68 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de gravitation [Termes IGN] convergence [Termes IGN] harmonique sphérique [Termes IGN] surface hétérogène [Termes IGN] transformation de Legendre [Termes IGN] transformation rapide de Fourier Résumé : (auteur) We present a method to integrate external solid spherical harmonic expansions at geographical grids residing on undulated surfaces. It can be used to evaluate area-mean potential values on planetary surfaces that vary within grid cells. This is in contrast with available methods, which assume cells with a constant spherical radius only. When formulating the technique, we took advantage of 2D spherical Fourier methods to improve the computational speed. The price to be paid are high memory requirements, even with moderate maximum harmonic degrees such as 100 (both of the potential and of the irregular surface). In numerical experiments, we validate the method against independent area-mean potential values to prove its correctness. A study of the series behavior below the sphere of convergence shows that the series may diverge on planetary topographies, similarly as it is with its point-value counterpart. The method can be utilized in numerical studies of the change of boundary method, one of the pivotal concepts of recent high-degree models such as EGM2008. A numerical implementation is made available through CHarm, a C library to work with spherical harmonics up to high degrees. CHarm is accessible via https://github.com/blazej-bucha/charm. Numéro de notice : A2022-736 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-022-01658-1 Date de publication en ligne : 27/09/2022 En ligne : https://doi.org/10.1007/s00190-022-01658-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=101708 [article]

Scale effect in indirect measurement of leaf area index / Guangjian Yan in IEEE Transactions on geoscience and remote sensing, vol 54 n° 6 (June 2016)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 54 n° 6 (June 2016) . - pp 3475 - 3484 Titre : Scale effect in indirect measurement of leaf area index Type de document : Article/Communication Auteurs : Guangjian Yan, Auteur ; Ronghai Hu, Auteur ; Yiting Wang, Auteur ; et al., Auteur Année de publication : 2016 Article en page(s) : pp 3475 - 3484 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] indice foliaire [Termes IGN] longueur [Termes IGN] mesure optique [Termes IGN] méthode de mesure [Termes IGN] modèle non linéaire [Termes IGN] surface hétérogène Résumé : (Auteur) Scale effect, which is caused by a combination of model nonlinearity and surface heterogeneity, has been of interest to the remote sensing community for decades. However, there is no current analysis of scale effect in the ground-based indirect measurement of leaf area index (LAI), where model nonlinearity and surface heterogeneity also exist. This paper examines the scale effect on the indirect measurement of LAI. We built multiscale data sets based on realistic scenes and field measurements. We then implemented five representative methods of indirect LAI measurement at scales (segment lengths) that range from meters to hundreds of meters. The results show varying degrees of deviation and fluctuation that exist in all five methods when the segment length is shorter than 20 m. The retrieved LAI from either Beer's law or the gap-size distribution method shows a decreasing trend with increasing segment lengths. The length at which the LAI values begin to stabilize is about a full period of row in row crops and 100 m in broadleaf or coniferous forests. The impacts of segment length on the finite-length averaging method, the combination of gap-size distribution and finite-length methods, and the path-length distribution method are relatively small. These three methods stabilize at the segment scale longer than 20 m in all scenes. We also find that computing the average LAI of all of the short segment lengths, which is commonly done, is not as good as merging these short segments into a longer one and computing the LAI value of the merged one. Numéro de notice : A2016-856 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2016.2519098 En ligne : https://doi.org/10.1109/TGRS.2016.2519098 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=82995 [article]

Using simulated Terrestrial Laser Scanning to analyse errors in high-resolution scan data of irregular surfaces / R. Hodge in ISPRS Journal of photogrammetry and remote sensing, vol 65 n° 2 (March - April 2010)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 65 n° 2 (March - April 2010) . - pp 227 - 240 Titre : Using simulated Terrestrial Laser Scanning to analyse errors in high-resolution scan data of irregular surfaces Type de document : Article/Communication Auteurs : R. Hodge, Auteur Année de publication : 2010 Article en page(s) : pp 227 - 240 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] erreur en position [Termes IGN] lasergrammétrie [Termes IGN] modèle numérique de surface [Termes IGN] semis de points [Termes IGN] simulation [Termes IGN] surface hétérogène [Termes IGN] télémétrie laser terrestre Résumé : (Auteur) Terrestrial Laser Scanning (TLS) is increasingly being used to collect mm-resolution surface data from a broad range of environments. When scanning complex surfaces, interactions between the surface topography, laser footprint and scanner precision can introduce errors into the point cloud. Quantification of these errors is, however, limited by the availability of independent measurement techniques. This research presents simulated TLS as a new approach to error quantification. Two sets of experiments are presented. The first set demonstrates that simulated TLS is able to reproduce real TLS data from a plane and a pebble. The second set uses simulated TLS to assess a methodology developed for the collection and processing of field TLS data. Simulated TLS data is collected from surfaces up to not, vert, similar1 m2 created from regular arrays of uniform spheres (sphere diameters of 10 to 100 mm) and irregular arrays of mixed spheres (median sphere diameters of 16 to 94 mm). These data were analysed to (i) assess the effectiveness of the processing methodology at removing erroneous points; (ii) quantify the magnitude of errors in a digital surface model (DSM) interpolated from the processed point cloud; and (iii) investigate the extent to which the interpolated DSMs retained the geometric properties of the original surfaces. The processing methodology was found to be effective, especially on data from coarser surfaces, with the retained points typically having an inter-quartile range (IQR) of point errors of not, vert, similar2 mm. DSM errors varied as a function of sphere size and packing, with DSM errors having an IQR of not, vert, similar2 mm for the regular surfaces and not, vert, similar4 mm for the irregular surfaces. Finally, whilst in the finer surfaces point and DSM errors were a substantial proportion of the sphere diameters, geometrical analysis indicated that the DSMs still reproduced properties of the original surface such as semivariance and some percentiles of the surface elevation distribution. Copyright ISPRS Numéro de notice : A2010-094 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2010.01.001 En ligne : https://doi.org/10.1016/j.isprsjprs.2010.01.001 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30290 [article]

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Estimation of regional evapotranspiration by TM/ETM+ data over heterogeneous surfaces / S. Liu in Photogrammetric Engineering & Remote Sensing, PERS, vol 73 n° 10 (October 2007)  

Public [article]  inPhotogrammetric Engineering & Remote Sensing, PERS > vol 73 n° 10 (October 2007) . - pp 1169 - 1178 Titre : Estimation of regional evapotranspiration by TM/ETM+ data over heterogeneous surfaces Type de document : Article/Communication Auteurs : S. Liu, Auteur ; G. Hu, Auteur ; et al., Auteur Année de publication : 2007 Article en page(s) : pp 1169 - 1178 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] analyse diachronique [Termes IGN] bilan hydrique [Termes IGN] données météorologiques [Termes IGN] estimation quantitative [Termes IGN] évapotranspiration [Termes IGN] image Landsat-ETM+ [Termes IGN] image Landsat-TM [Termes IGN] Pékin (Chine) [Termes IGN] surface hétérogène Résumé : (Auteur) Evapotranspiration is an important part in surface energy balance and water balance. Compared with other methods (micrometeorological, climatological, or hydrological method), the remote sensing model has obvious superiority to estimate regional evapotranspiration over heterogeneous surfaces. In this study, based on Landsat TM/ETM+ data and meteorological data, evapotranspiration in Beijing area on 17 April 2001, 12 April 2002, 06 July 2004, 06 May 2005, and 22 May 2005 were calculated by an estimation model of regional evapotranspiration. Comparisons of energy balance components (net radiation, soil heat flux, sensible and latent heat flux) with measured fluxes were made integrating the remotely sensed fluxes by the footprint model. Results show that latent heat flux estimates (adjusted for closure) with errors (MBE1RMSE) 26.47142.54 Wm-2, sensible heat flux error of -8.56123.79 Wm-2, net radiation error of 25.16150.87 Wm-2 and soil heat flux error of 10.68122.81 Wm-2. The better agreement between the estimates and the measurements indicates that the remote sensing model is appropriate for estimating regional evapotranspiration over heterogeneous surfaces. Furthermore, the spatial distribution of evapotranspiration in Beijing area was analyzed. Copyright ASPRS Numéro de notice : A2007-477 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.14358/PERS.73.10.1169 En ligne : https://doi.org/10.14358/PERS.73.10.1169 Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28840 [article]