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Above-ground biomass estimation and yield prediction in potato by using UAV-based RGB and hyperspectral imaging / Bo Li in ISPRS Journal of photogrammetry and remote sensing, vol 162 (April 2020)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 162 (April 2020) . - pp 161 -1 72 Titre : Above-ground biomass estimation and yield prediction in potato by using UAV-based RGB and hyperspectral imaging Type de document : Article/Communication Auteurs : Bo Li, Auteur ; Xiangming Xu, Auteur ; Li Zhang, Auteur Année de publication : 2020 Article en page(s) : pp 161 -1 72 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] biomasse aérienne [Termes IGN] classification par forêts d'arbres décisionnels [Termes IGN] couvert végétal [Termes IGN] hauteur de la végétation [Termes IGN] image captée par drone [Termes IGN] image hyperspectrale [Termes IGN] image RVB [Termes IGN] indice de végétation [Termes IGN] pomme de terre [Termes IGN] régression des moindres carrés partiels [Termes IGN] rendement agricole Résumé : (auteur) Rapid and accurate biomass and yield estimation facilitates efficient plant phenotyping and site-specific crop management. A low altitude unmanned aerial vehicle (UAV) was used to acquire RGB and hyperspectral imaging data for a potato crop canopy at two growth stages to estimate the above-ground biomass and predict crop yield. Field experiments included six cultivars and multiple treatments of nitrogen, potassium, and mixed compound fertilisers. Crop height was estimated using the difference between digital surface model and digital elevation models derived from RGB imagery. Combining with two narrow-band vegetation indices selected by the RReliefF feature selection algorithm. Random Forest regression models demonstrated high prediction accuracy for both fresh and dry above-ground biomass, with a coefficient of determination (r2) > 0.90. Crop yield was predicted using four narrow-band vegetation indices and crop height (r2 = 0.63) with imagery data obtained 90 days after planting. A Partial Least Squares regression model based on the full wavelength spectra demonstrated improved yield prediction (r2 = 0.81). This study demonstrated the merits of UAV-based RGB and hyperspectral imaging for estimating the above-ground biomass and yield of potato crops, which can be used to assist in site-specific crop management. Numéro de notice : A2020-125 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2020.02.013 Date de publication en ligne : 28/02/2020 En ligne : https://doi.org/10.1016/j.isprsjprs.2020.02.013 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94750 [article]

Reducing multipath effect of low-cost GNSS receivers for monitoring by considering temporal correlations / Li Zhang in Journal of applied geodesy, vol 14 n° 2 (April 2020)  

Public [article]  inJournal of applied geodesy > vol 14 n° 2 (April 2020) . - pp 167 – 175 Titre : Reducing multipath effect of low-cost GNSS receivers for monitoring by considering temporal correlations Type de document : Article/Communication Auteurs : Li Zhang, Auteur ; Volker Schwieger, Auteur Année de publication : 2020 Article en page(s) : pp 167 – 175 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] atténuation du signal [Termes IGN] corrélation temporelle [Termes IGN] coût [Termes IGN] itération [Termes IGN] ligne de base [Termes IGN] oscillation [Termes IGN] phase [Termes IGN] plan de masse [Termes IGN] qualité des données [Termes IGN] récepteur GNSS [Termes IGN] récepteur monofréquence [Termes IGN] réflecteur [Termes IGN] source d'erreur [Termes IGN] trajet multiple Résumé : (auteur) The investigations on low-cost single frequency GNSS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox GNSS receivers combined with low-cost antennas and self-constructed L1-optimized choke rings can reach an accuracy which almost meets the requirements of geodetic applications (see Zhang and Schwieger [25]). However, the quality (accuracy and reliability) of low-cost GNSS receiver data should still be improved, particularly in environments with obstructions. The multipath effects are a major error source for the short baselines. The ground plate or the choke ring ground plane can reduce the multipath signals from the horizontal reflector (e. g. ground). However, the shieldings cannot reduce the multipath signals from the vertical reflectors (e. g. walls). Because multipath effects are spatially and temporally correlated, an algorithm is developed for reducing the multipath effect by considering the spatial correlations of the adjoined stations (see Zhang and Schwieger [24]). In this paper, an algorithm based on the temporal correlations will be introduced. The developed algorithm is based on the periodic behavior of the estimated coordinates and not on carrier phase raw data, which is easy to use. Because, for the users, coordinates are more accessible than the raw data. The multipath effect can cause periodic oscillations but the periods change over time. Besides this, the multipath effect’s influence on the coordinates is a mixture of different multipath signals from different satellites and different reflectors. These two properties will be used to reduce the multipath effect. The algorithm runs in two steps and iteratively. Test measurements were carried out in a multipath intensive environment; the accuracies of the measurements are improved by about 50 % and the results can be delivered in near-real-time (in ca. 30 minutes), therefore the algorithm is suitable for structural health monitoring applications. Numéro de notice : A2020-217 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2019-0059 Date de publication en ligne : 27/03/2020 En ligne : https://doi.org/10.1515/jag-2019-0059 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94910 [article]

Improving the quality of low-cost GPS receiver data for monitoring using spatial correlations / Li Zhang in Journal of applied geodesy, vol 10 n° 2 (June 2016)  

Public [article]  inJournal of applied geodesy > vol 10 n° 2 (June 2016) . - pp 119 - 129 Titre : Improving the quality of low-cost GPS receiver data for monitoring using spatial correlations Type de document : Article/Communication Auteurs : Li Zhang, Auteur ; Volker Schwieger, Auteur Année de publication : 2016 Article en page(s) : pp 119 - 129 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] correction du trajet multiple [Termes IGN] corrélation automatique de points homologues [Termes IGN] coût [Termes IGN] récepteur GPS [Termes IGN] récepteur monofréquence [Vedettes matières IGN] Traitement de données GNSS Résumé : (auteur) The investigations on low-cost single frequency GPS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox LEA-6T GPS receivers combined with Trimble Bullet III GPS antennas containing self-constructed L1-optimized choke rings can already obtain an accuracy in the range of millimeters which meets the requirements of geodetic precise monitoring applications (see [27]). However, the quality (accuracy and reliability) of low-cost GPS receiver data, particularly in shadowing environment, should still be improved, since the multipath effects are the major error for the short baselines. For this purpose, several adjoined stations with low-cost GPS receivers and antennas were set up next to the metal wall on the roof of the IIGS building and measured statically for several days. The time series of three-dimensional coordinates of the GPS receivers were analyzed. Spatial correlations between the adjoined stations, possibly caused by multipath effect, will be taken into account. The coordinates of one station can be corrected using the spatial correlations of the adjoined stations, so that the quality of the GPS measurements is improved. The developed algorithms are based on the coordinates and the results will be delivered in near-real-time (in about 30 minutes), so that they are suitable for structural health monitoring applications. Numéro de notice : A2016-559 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2015-0022 En ligne : http://dx.doi.org/10.1515/jag-2015-0022 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81738 [article]

Geostatistical estimation of signal-to-noise ratios for spectral vegetation indices / L. Ji in ISPRS Journal of photogrammetry and remote sensing, vol 96 (October 2014)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 96 (October 2014) . - pp 20 - 47 Titre : Geostatistical estimation of signal-to-noise ratios for spectral vegetation indices Type de document : Article/Communication Auteurs : L. Ji, Auteur ; Li Zhang, Auteur ; Jennifer Rover, Auteur Année de publication : 2014 Article en page(s) : pp 20 - 47 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] bruit (théorie du signal) [Termes IGN] estimation statistique [Termes IGN] géostatistique [Termes IGN] indice de végétation Résumé : (Auteur) In the past 40 years, many spectral vegetation indices have been developed to quantify vegetation biophysical parameters. An ideal vegetation index should contain the maximum level of signal related to specific biophysical characteristics and the minimum level of noise such as background soil influences and atmospheric effects. However, accurate quantification of signal and noise in a vegetation index remains a challenge, because it requires a large number of field measurements or laboratory experiments. In this study, we applied a geostatistical method to estimate signal-to-noise ratio (S/N) for spectral vegetation indices. Based on the sample semivariogram of vegetation index images, we used the standardized noise to quantify the noise component of vegetation indices. In a case study in the grasslands and shrublands of the western United States, we demonstrated the geostatistical method for evaluating S/N for a series of soil-adjusted vegetation indices derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. The soil-adjusted vegetation indices were found to have higher S/N values than the traditional normalized difference vegetation index (NDVI) and simple ratio (SR) in the sparsely vegetated areas. This study shows that the proposed geostatistical analysis can constitute an efficient technique for estimating signal and noise components in vegetation indices. Numéro de notice : A2014-382 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2014.06.013 En ligne : https://doi.org/10.1016/j.isprsjprs.2014.06.013 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=73809 [article]

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Tests and performance evaluation of DMC images and new methods for their processing / Li Zhang in Revue Française de Photogrammétrie et de Télédétection, n° 183 (Septembre 2006)

Public [article]  inRevue Française de Photogrammétrie et de Télédétection > n° 183 (Septembre 2006) . - pp 67 - 74 Titre : Tests and performance evaluation of DMC images and new methods for their processing Type de document : Article/Communication Auteurs : Li Zhang, Auteur ; S. Kocaman, Auteur ; et al., Auteur Année de publication : 2006 Conférence : ISPRS 2006, Commission 1 Symposium, From sensors to imagery 03/07/2006 06/07/2006 Champs-sur-Marne [Paris Marne-la-Vallée] France OA ISPRS Archives Article en page(s) : pp 67 - 74 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] chambre DTC [Termes IGN] DMC [Termes IGN] image aérienne [Termes IGN] image numérique [Termes IGN] point d'appui [Termes IGN] points homologues [Termes IGN] précision géométrique (imagerie) [Termes IGN] test de performance [Termes IGN] traitement d'image [Termes IGN] valeur radiométrique Résumé : (Auteur) The Cartographic Institute of Catalonia (ICC) has acquired a DMC digital camera and has performed some first investigations regarding radiometric performance and geometric accuracy potential. In this cooperation with the Institute of Geodesy and Photogrammetry (IGP), ETH Zurich various aspects are analysed. The investigations make use of recent test flights near Tortosa, a plane region with varying landcover. For the quantitative analysis of the DMC results, a ground control points and lidar data exist, which have been simultaneously acquired with the DMC images. The first part of the investigations focusses on geometric sensor modeling and aerial triangulation. Preliminary results of ICC have shown that when standard additional parameters, like the 12 Ebner parameters, are used in AT, significant systematic errors remain and each of the 4 subimages that form the virtual panchromatic image has a different pattern of image deformations. In these investigations, we do not perform analysis of additional parameters in order to model these deformations, as this has been done in another ICC work. The results are analysed using GCPs established in the above mentioned testfield, using two different bundle adjustment programs.. Another part of our investigations regarding AT deals with automatic point transfer using a high quality multi-image, multi-primitive matching method developed at IGP, initially for automatic DSM generation. Different aspects like number, distribution and accuracy of the tie points are analysed, as well number of rays per tie point. The second part of the paper focuses on automatic DSM generation. Although digital cameras offer characteristics, like better image quality, that could be used favourably in automated DSM generation, almost all commercial systems employ matching methods with limitations, like no support of multi-image matching. In these investigations, we briefly introduce the above mentioned IGP multi-image matching and present the matching results. Initial results with other digital cameras and images with large forward and side overlap have shown that this matching approach can produce DSMs at least as dense as those produced by airborne laser scanning and almost as accurate, preserving also very well surface discontinuities. The processing and DSM control was performed by IGP using lidar data provided by ICC, while ICC made an independent control of the aerial triangulation using the software programs at ICC. Copyright SFPT Numéro de notice : A2006-630 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28353 [article]

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Multi-image matching for DSM generation from Ikonos imagery / Li Zhang in ISPRS Journal of photogrammetry and remote sensing, vol 60 n° 3 (May 2006)  

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Automatic Digital Surface Model (DSM) generation from linear array images / Li Zhang (2005)  

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