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A wavelet-based echo detector for waveform LiDAR data / Cheng-Kai Wang in IEEE Transactions on geoscience and remote sensing, vol 54 n° 2 (February 2016)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 54 n° 2 (February 2016) . - pp 757 - 769 Titre : A wavelet-based echo detector for waveform LiDAR data Type de document : Article/Communication Auteurs : Cheng-Kai Wang, Auteur ; Yi-Hsing Tseng, Auteur ; Chi-Kuei Wang, Auteur Année de publication : 2016 Article en page(s) : pp 757 - 769 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] données lidar [Termes IGN] forme d'onde [Termes IGN] modèle numérique de surface [Termes IGN] onde lidar [Termes IGN] ondelette [Termes IGN] semis de points [Termes IGN] signal laser Résumé : (Auteur) This paper presents a wavelet-based (WB) echo detector that can recover the echoes missed by a light detection and ranging (LiDAR) system via on-the-fly detection. An on-the-fly detection method normally utilizes a simple threshold (TH) to register a target point. Points that belong to weak and/or overlapping echoes are much complicated and are easily missed by TH approaches. The proposed detector based on wavelet transformation is robust to noise and is capable of resolving overlapping echoes. It is thus expected to be good at handling missing echoes. A simulated waveform data set and a real waveform data set of a forest area were both used in this paper. The simulated waveform data were utilized to compare the proposed detector with zero crossing (ZC) and Gaussian decomposition (GD) detectors in terms of their ability to deal with weak or overlapping echoes. The real waveform data set acquired from Leica ALS60 was used to demonstrate a WB algorithm for exploring the missing echoes. Experiments using the simulated data showed that the WB and GD detectors are superior to the ZC detector in finding overlapping echoes. The WB algorithm performs well when dealing with overlapping echoes with a low signal-to-noise ratio. Experiments using the real waveform data show that 31.5% additional weak or overlapping echoes can be detected by the WB detector compared with the point cloud provided by the system. With such additional points, the mean and root-mean-square errors of the digital elevation model differences can be improved from 0.72 and 0.79 m to 0.16 and 0.59 m, respectively. Numéro de notice : A2016-119 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2015.2465148 En ligne : https://doi.org/10.1109/TGRS.2015.2465148 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79999 [article]

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DEM measurements of a gravel-bed surface using two scales of images / Chi-Kuei Wang in Photogrammetric record, vol 30 n° 152 (December 2015 - February 2016)  

Public [article]  inPhotogrammetric record > vol 30 n° 152 (December 2015 - February 2016) . - pp 387 - 401 Titre : DEM measurements of a gravel-bed surface using two scales of images Type de document : Article/Communication Auteurs : Chi-Kuei Wang, Auteur ; Jui-Teng Chung, Auteur ; Yu-Li Lin, Auteur Année de publication : 2015 Article en page(s) : pp 387 - 401 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications photogrammétriques [Termes IGN] gravier [Termes IGN] limite de résolution géométrique [Termes IGN] lit [Termes IGN] modèle numérique de surface [Termes IGN] photogrammétrie terrestre [Termes IGN] rivière [Termes IGN] Taïwan Résumé : (auteur) Determining the geometry of an exposed gravel-bed surface is important in understanding river flow characteristics. This study presents a method of generating a digital elevation model (DEM) of exposed gravel-bed surfaces using two different scales of images of a riverine environment. The small scale DEM covers an area of 4·5 m × 4·5 m and serves as the reference base, whereas several large scale DEMs provide highly detailed elevation information along the site diagonals. The equipment includes a consumer-grade camera and is light and easy to set up in the field. Highly automated procedures using several off-the-shelf packages ease the burden of generating DEMs of the gravel-bed surface, reducing the technological obstacles for other disciplines. This study evaluates the accuracy of the proposed method at three study sites with different grain sizes along the Hou-Jue River in southern Taiwan. The elevation accuracy obtained by the proposed method was validated by a total station and achieved a root mean square error of 2·9 to 4·3 mm. Numéro de notice : A2015-828 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.1111/phor.12125 Date de publication en ligne : 15/12/2015 En ligne : https://doi.org/10.1111/phor.12125 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79124 [article]

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