References of "Lejeune, Philippe"
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See detailMulti-temporal monitoring of a regional riparian buffer network (>12,000 km) with LiDAR and photogrammetric point clouds
Michez, Adrien ULiege; Piégay, Hervé; Lejeune, Philippe ULiege et al

in Journal of Environmental Management (in press)

Riparian buffers are of major concern for land and water resource managers despite their relatively low spatial coverage. In Europe, this concern has been acknowledged by different environmental ... [more ▼]

Riparian buffers are of major concern for land and water resource managers despite their relatively low spatial coverage. In Europe, this concern has been acknowledged by different environmental directives which recommend multi-scale monitoring (from local to regional scales). Remote sensing methods could be a cost-effective alternative to field-based monitoring, to build replicable “wall-to-wall” monitoring strategies of large river networks and associated riparian buffers. The main goal of our study is to extract and analyze various parameters of the riparian buffers of up to 12,000 km of river in southern Belgium (Wallonia) from three-dimensional (3D) point clouds based on LiDAR and photogrammetric surveys to i) map riparian buffers parameters on different scales, ii) interpret the regional patterns of the riparian buffers and iii) propose new riparian buffer management indicators. We propose different strategies to synthesize and visualize relevant information at different spatial scales ranging from local (<10 km) to regional scale (>12,000 km). Our results showed that the selected parameters had a clear regional pattern. The reaches of Ardenne ecoregion have channels with the highest flow widths and shallowest depths. In contrast, the reaches of the Loam ecoregion have the narrowest and deepest flow channels. Regional variability in channel width and depth is used to locate management units potentially affected by human impact. Riparian forest of the Loam ecoregion is characterized by the lowest longitudinal continuity and mean tree height, underlining significant human disturbance. As the availability of 3D point clouds at the regional scale is constantly growing, our study proposes reproducible methods which can be integrated into regional monitoring by land managers. With LiDAR still being relatively expensive to acquire, the use of photogrammetric point clouds combined with LiDAR data is a cost-effective means to update the characterization of the riparian forest conditions. [less ▲]

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See detailQuantification of anthropogenic effects in the landscape of Lubumbashi
Andre, Marie ULiege; Vranken, Isabelle ULiege; Boisson, Sylvain ULiege et al

in Mahy, Grégory; Colinet, Gilles; Bogaert, Jan (Eds.) Anthropisation au Katanga (in press)

In order to understand the dynamic of the (sub)urbanisation and so, to quantify the anthropogenic effects of the rapid growth of tropical cities, it is crucial to find and apply valuable methods. In this ... [more ▼]

In order to understand the dynamic of the (sub)urbanisation and so, to quantify the anthropogenic effects of the rapid growth of tropical cities, it is crucial to find and apply valuable methods. In this contribution, the transferability of the Rüdisser et al. (2012) «Distance to Nature» hemeroby assessment method to the landscape surrounding the city of Lubumbashi (DRC) is evaluated. That methodology has the advantage of taking structural connectivity into account by computing the distance to natural habitats. As it had never been applied to an African city before, some adjustments (fitting of the local land uses types into the hemeroby levels designed to Austria) and amendments (suppression of the final classification into hemeroby level simplification) are proposed. Moreover, an analysis of the decanal (2002-2013) hemeroby dynamics is presented. Results suggest that the Distance to Nature methodology is transferable but requires good field knowledge to define reference habitats and identify them in the Landsat classified images. There was a dramatic decrease of the «natural» and «near-natural» levels in the study extent during the studied period. In addition, 32% of the land underwent anthropisation increase, mostly around cities and following a ribbon development. [less ▲]

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See detailUpscaling winter wheat above-ground biomass measurements using multispectral imagery and 3D data from unmanned aerial vehicle
Michez, Adrien ULiege; Bauwens, Sébastien ULiege; Heinesch, Bernard ULiege et al

Poster (2017, October 20)

Field measurements in the ICOS program are spatially limited whereas the monitored gas fluxes may have a large footprint. Aerial remote sensing has the advantage to monitor large areas. The main goal of ... [more ▼]

Field measurements in the ICOS program are spatially limited whereas the monitored gas fluxes may have a large footprint. Aerial remote sensing has the advantage to monitor large areas. The main goal of our research was to test the potential of unmanned aerial vehicles (UAV) to upscale parameters monitored through the ICOS program. In this study, we specifically focus on above-ground biomass (AGB) monitoring in a winter wheat crop. We used a octocopter drone (X frame type) to acquire a time series over the crop growing season (8 flights from the 14th of February 2017 to the 7th of July 2017) of multispectral imagery covering the ICOS candidate station of Lonzée (Wallonia, Belgium) and the surrounding field crop areas (ca. 0.25 km² per flight). The multispectral camera provides spectral information on the green (550 +/- 50 nm), red (660 +/- 50 nm), near infrared (735 +/- 50 nm) and red-edge (790 +/- 10 nm) wavelengths bands. The UAV also brought an off-the-shelf high resolution (20 Mpx) RGB camera to derive accurate 3D data. We performed a photogrammetric 3D reconstruction of the acquired imagery for every flight survey. The images provided by the RGB sensor (Sony RX100) were used to produce a high spatial resolution Digital Surface Model (0.05 m) and the images acquired by the multispectral sensor were used to derive reflectance maps (0.1 m) in the four wavelengths bands. The four reflectance layers were combined to produce two straight-forward vegetation indices (Normalized Difference Vegetation Index and Green NDVI). The photogrammetric DSM’s were combined to a LiDAR Digital Terrain Model (public database, survey in winter 2013) to produce Crop Height Models (CHM) of the study area. We used multiple linear regressions modelling in order to predict the AGB of the field crop monitored by the ICOS station of Lonzée with UAV imagery. AGB=a+b*GNDVI+c*NDVI+d *CHM The field crop data were provided by the ICOS program and by field research conducted in experimental field crops close to the flux tower. The field sampling consisted in destructive samples of the crop which were weighted after drying. For each field sample, an associated area was computed based on the outdistance sowing and the number of sampled crops in order to compute an AGB per area unit (t / Ha). Each AGB field estimation was associated to the closest flight date to build a multi date model presenting good performances (r² = 0.85, RMSE = 2.3 t/Ha). We used the same modelling approach to adjust a single date model to derive a predicted AGB map for the 7th of July. The performance of the single date model is lower but still highlights the biomass variation within the crop (r² = 0.71, RMSE = 1.9 t/Ha). The predicted AGB map displays a high spatial heterogeneity with some spatial patterns. Locally low AGB values are found along two old pedestrian whereas higher AGB values can be associated to areas which were sprayed twice (in-between two tractor tracks). Our results highlight the potential of UAV multispectral imagery to monitor the AGB variation within the footprint of the flux tower and highlight the need for repeated field sampling with a precise geolocation to improve the matching between the flight and the field surveys. [less ▲]

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See detailIdentification of the anteroposterior and mediolateral position of lion paws and tracks using 3D geometric morphometrics
Marchal, Antoine F.J.; Lejeune, Philippe ULiege; de Bruyn, P.J. Nico

in African Journal of Wildlife Research (2017), 47(2), 106-113

Estimating the distribution and status of animal populations is crucial in various fields of biology. Monitoring species via their tracks is controversial due to unreliable recording techniques ... [more ▼]

Estimating the distribution and status of animal populations is crucial in various fields of biology. Monitoring species via their tracks is controversial due to unreliable recording techniques, manipulator bias and substrate variation. Furthermore, subjective identification of the foot that produces each track can lead to significant errors, for example, when assigning tracks made by different feet from the same individual to different individuals. The aim of this research was to develop an accurate, consistent and objective algorithm to identify the anteroposterior (hind/front) and mediolateral (right/left) position from digital threedimensional (3D) models of African lion (Panthera leo) paws and tracks using geometric morphometrics. We manually positioned 12 fixed landmarks on 132 paws and 182 tracks recorded in 3D using digital close-range photogrammetry. We used geometric morphometrics to evaluate and visualize the shape variation between paws and between tracks along the anteroposterior and mediolateral axes, and between paws and tracks. The identification algorithm using linear discriminant analysis with jack-knifed predictions reached a maximum accuracy of 95.45% and 91.21% for paws and tracks, respectively.We recommend the use of this objective position identification algorithm in future studies where tracks are compared between individual African lions. [less ▲]

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See detailComparison of UAS photogrammetric products for tree detection and characterization of coniferous stands
Bonnet, Stéphanie ULiege; Lisein, Jonathan ULiege; Lejeune, Philippe ULiege

in International Journal of Remote Sensing (2017), 38(19), 5310-5337

The use of Unmanned Aerial Systems (UAS) opens a new era for remote sensing and forest management, which requires accurate and regular quantification of resources. In this study, we propose a ... [more ▼]

The use of Unmanned Aerial Systems (UAS) opens a new era for remote sensing and forest management, which requires accurate and regular quantification of resources. In this study, we propose a comprehensive workflow to detect trees and assess forest attributes in the particular context of coniferous stands in transformation from even-aged to uneven-aged stands, using UAS imagery, from data acquisition to model construction. We implement a local maxima detection to identify the tree tops, based on a fixed-radius moving window in a Canopy Height Model (CHM) and images produced from UAS surveys. To compare the contribution of different photogrammetric products, we analysed the local maxima detected from the CHM, from three image types (individual rectified and ortho-rectified images and ortho-mosaic) and from a combination of both CHM and images. The local maxima detection gave promising results, with low omission and true-positive rates of up to 89.2%. A filtering process of false positives was implemented, using a supervised classification which decreased the false positives up to 2.6%. Based on the local maxima combined with an area-based approach, we constructed models to assess top height (R2: 83%, root mean square error [RMSE]: 5.7%), number of stems (R2: 71%, RMSE: 28.3%), basal area (R2: 70%, RMSE: 16.2%), volume (R2: 69%, RMSE: 20.1%), and individual tree height (R2: 70%, RMSE: 7.2%). Despite a suboptimal data acquisition, our simple and flexible method has yielded good results and shows great potential for application. [less ▲]

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See detailPresent-day central African forest is a legacy of the 19th century human history
Morin, Julie ULiege; Fayolle, Adeline ULiege; Favier, Charly et al

in eLife (2017)

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850 ... [more ▼]

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850) after major anthropogenic disturbances ceased. Since 1885, less itinerancy and disturbance in the forest has occurred because the colonial administrations concentrated people and villages along the primary communication axes. Local populations formerly gardened the forest by creating scattered openings, which were sufficiently large for the establishment of light-demanding trees. Currently, common logging operations do not create suitable openings for the regeneration of these species, whereas deforestation degrades landscapes. Using an interdisciplinary approach, which included paleoecological, archaeological, historical, and dendrological data, we highlight the long-term history of human activities across central African forests and assess the contribution of these activities to present-day forest structure and composition. The conclusions of this sobering analysis present challenges to current silvicultural practices and to those of the future. [less ▲]

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See detailDétection de l’érosion dans un bassin versant agricole par comparaison d’images multidates acquises par drone
Lisein, Jonahtan; Pineux, Nathalie; Pierrot-Deseilligny, Marc et al

in Revue française de Photogrammétrie et de Télédétection (2017), 213-214(janvier-avril), 133-141

L’émergence des drones comme outils de cartographie rapide, de par leur capacité à répondre à des besoins très spécifiques, offre de nombreuses opportunités aux scientifiques. Par ailleurs, les récentes ... [more ▼]

L’émergence des drones comme outils de cartographie rapide, de par leur capacité à répondre à des besoins très spécifiques, offre de nombreuses opportunités aux scientifiques. Par ailleurs, les récentes évolutions des techniques de photogrammétrie et de vision par ordinateur permettent, à partir de prises de vues aériennes stéréoscopiques, de fournir aux géomorphologues et aux hydrologues des données topographiques à haute résolution (Tarolli, 2014). En effet, les algorithmes d’orientation externe (structure from motion en anglais, Snavely et al. (2008)) permettent la détermination automatique de la position et de l’orientation des prises de vue d’une collection d’images se recouvrant. La corrélation dense automatique permet ensuite, depuis un bloc d’images orientées, de modéliser finement le relief. L’utilisation en géomorphologie de drones pour la modélisation du relief en est encore à ses premiers souffles, mais montre un potentiel très intéressant. La précision des mesures photogrammétriques rivalise en effet avec les relevés LiDAR, pour un coût d’acquisition significativement moins élevé. Cette recherche se focalise sur deux objectifs. Le premier est de déterminer si la précision des mesures photogrammétriques issues d’images acquises avec un mini-drone permet la détection de changement de relief très fin via la comparaison d’acquisitions multi-dates. Le deuxième objectif, plus spécifique, est de déterminer la manière la plus optimale de paramétrer la compensation par faisceaux avec points d’appui au sein de la suite photogrammétrique open-source MICMAC. [less ▲]

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See detailFrom tracks to fine-scale movement modes:a straightforward approach for identifying multiple spatial movement patterns
Morelle, Kévin; Bunnefeld, Nils; Lejeune, Philippe ULiege et al

in Methods in Ecology and Evolution (2017)

1. Thanks to developments in animal tracking technology, detailed data on the movement tracks of individual animals are now attainable for many species. However, straightforward methods to decompose ... [more ▼]

1. Thanks to developments in animal tracking technology, detailed data on the movement tracks of individual animals are now attainable for many species. However, straightforward methods to decompose individual tracks into high-resolution, spatial modes are lacking but are essential to understand what an animal is doing. 2. We developed an analytical approach that combines separately validated methods into a straightforward tool for converting animal GPS tracks into short-range movement modes. Our three-step analytical process comprises: (i) decomposing data into separate movement segments using behavioural change point analysis; (ii) defining candidate movement modes and translating them into nonlinear or linear equations between net squared displacement (NSD) and time and (iii) fitting each candidate equation to NSD segments and determining the best-fitting modes using Concordance Criteria, Akaike's Information Criteria and other fine-scale segment characteristics. We illustrate our approach for three sub-adults, male wild boar Sus scrofa tracked at 15-min intervals over 4 months using GPS collars. We defined five candidate movement modes based on previously published studies of short-term movements: encamped, ranging, round trips (complete and partial) and wandering. 3. Our approach successfully classified over 80% of the tracks into these movement modes lasting between 5 and 54 h and covering between 300 m to 20 km. Repeated analyses of GPS data resampled at different rates indicated that one positional fix every 3–4 h was sufficient for >70% classification success. Classified modes were consistent with published observations of wild boar movement, further validating our method. 4. The proposed approach advances the status quo by permitting classification into multiple movement modes (where these are adequately discernable from spatial fixes) facilitating analyses at high temporal and spatial resolutions, and is straightforward, largely objective, and without restrictive assumptions, necessary parameterizations or visual interpretation. Thus, it should capture the complexity and variability of tracked animal movement mode for a variety of taxa across a wide range of spatial and temporal scales. [less ▲]

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See detailIdentification of sprinkling storage facilities for windblown timber using a GIS-based modeling approach
Riguelle, Simon ULiege; Jourez, Benoît ULiege; Hebert, Jacques ULiege et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment (2017), 21(2),

After catastrophic storm events, the storage of windblown timber is an effective measure for mitigating economic losses in the forest sector by preventing wood decay, protecting stands from secondary ... [more ▼]

After catastrophic storm events, the storage of windblown timber is an effective measure for mitigating economic losses in the forest sector by preventing wood decay, protecting stands from secondary damage, and regulating the timber supply in the middle and long term. In this study, we first propose a GIS-based methodology for identifying suitable sprinkling storage terminals in Wallonia (Belgium). In addition, we suggest an approach for building a coherent regional network as well as methods for selecting and activating terminals within this network after a storm, depending on the severity and distribution of the damage. The GIS-based approach was used to crosscheck technical requirements related to sprinkling storage according to operational and environmental constraints in the Ardenne, which is the most forested sub-region of Wallonia. A three-step process was employed to identify suitable areas. Nine procurement areas were also delineated according to the regional forest inventory plots as a reference for choosing the terminals that should be included in the regional network and activated after the storm. We generated and evaluated 96 scenarios. In the second step, a network of 30 terminals was suggested, which corresponded to a storage capacity of 4 million m³. This network could facilitate the flexibility in the strategic management of storage after huge storms. The procurement area approach also helps addressing routing and transportation issues in a simple way. The GIS approach facilitates the selection of sprinkling storage terminals, but field validation and enhanced collaboration between public and private landowners and forest owners would still be needed. [less ▲]

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See detailCan DEM time series produced by UAV be used to quantify diffuse erosion in an agricultural watershed?
Pineux, Nathalie ULiege; Lisein, Jonathan ULiege; Swerts, Gilles ULiege et al

in Geomorphology (2017), 280

Erosion and deposition modelling should rely on field data. Currently these data are seldom available at large spatial scales and/or at high spatial resolution. In addition, conventional erosion ... [more ▼]

Erosion and deposition modelling should rely on field data. Currently these data are seldom available at large spatial scales and/or at high spatial resolution. In addition, conventional erosion monitoring approaches are labour intensive and costly. This calls for the development of new approaches for field erosion data acquisition. As a result of rapid technological developments and low cost, unmanned aerial vehicles (UAV) have recently become an attractive means of generating high resolution digital elevation models (DEMs). The use of UAV to observe and quantify gully erosion is now widely established. However, in some agro-pedological contexts, soil erosion results from multiple processes, including sheet and rill erosion, tillage erosion and erosion due to harvest of root crops. These diffuse erosion processes often represent a particular challenge because of the limited elevation changes they induce. In this study,we propose to assess the reliability and development perspectives of UAV to locate and quantify erosion and deposition in a context of an agricultural watershed with silt loam soils and a smooth relief. Erosion and deposition rates derived from high resolution DEM time series are compared to field measurements. The UAV technique demonstrates a high level of flexibility and can be used, for instance, after a major erosive event. It delivers a very high resolution DEM(pixel size: 6 cm) which allows us to compute high resolution runoff pathways. This could enable us to precisely locate runoff management practices such as fascines. Furthermore, the DEMs can be used diachronically to extract elevation differences before and after a strongly erosive rainfall and be validated by field measurements. While the analysis for this study was carried out over 2 years, we observed a tendency along the slope from erosion to deposition. Erosion and deposition patterns detected at the watershed scale are also promising. Nevertheless, further development in the processing workflow of UAV data is required in order to make this technique accurate and robust enough for detecting sediment movements in an agricultural watershed affected by diffuse erosion. This area of investigation holdsmuch potential as the images processing is relatively new and expanding. [less ▲]

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See detailCaractérisation des forêts à l’aide de la technologie lidar
Michez, Adrien ULiege; Bauwens, Sébastien ULiege; Bonnet, Stéphanie ULiege et al

in Baghdadi, Nicolas; Zribi, Mehrez (Eds.) Observation des Surfaces Continentales par Télédétection: Agriculture et Forêt (2016)

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See detailEvolution récente des surface forestières et de la régénération des coupes rases en Wallonie
Latte, Nicolas ULiege; Perin, Jérôme ULiege; Lejeune, Philippe ULiege

in FORÊT.NATURE (2016), 141

Une gestion réfléchie de la ressource forestière à l’échelle d’une région, telle que la Wallonie, nécessite de connaitre son état et de prédire son devenir. Pour y parvenir, nous proposons une méthode ... [more ▼]

Une gestion réfléchie de la ressource forestière à l’échelle d’une région, telle que la Wallonie, nécessite de connaitre son état et de prédire son devenir. Pour y parvenir, nous proposons une méthode relativement simple, combinant trois sources de données : l’inventaire forestier régional, la photo-interprétation d’orthoimages et une enquête de terrain, ayant comme finalité de décrire finement l’évolution des surfaces forestières, les peuplements mis à blanc et la régénération des coupes rases. [less ▲]

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See detailUse of Unmanned Aerial System to assess wildlife (Sus scrofa) damage to crops (Zea mays)
Michez, Adrien ULiege; Morelle, Kevin; Lehaire, François et al

in Journal of Unmanned Vehicle Systems (2016), 4(4)

Damage caused by ungulates to agricultural areas are difficult to evaluate because the real extent of the damage remains usually poorly described and potentially arising conflicts. Recent advances in ... [more ▼]

Damage caused by ungulates to agricultural areas are difficult to evaluate because the real extent of the damage remains usually poorly described and potentially arising conflicts. Recent advances in unmanned aerial system (UAS) provide new versatile mapping and quantification possibilities in a wide range of applications. We used crop fields (Zea mays) damaged by wild boar (Sus scrofa) and compared the extent of the damage by means of three methods: i) traditional ground-based assessment ii) UAS orthoimages with operator delineation and iii) UAS Crop Height Model with automatic delineation based on height threshold. We showed for the first time that UAS could be applied for assessing damage of ungulates to agriculture. The two methods using UAS imagery provide coherent and satisfactory results and trended to underestimate the damage area when compared to in-use ground-based field expertise. However we suggest that performance of UAS should further be tested in variable conditions in order to assess the broad application of this tool. Our study describes the potential of UAS as a tool for estimating more accurately the damage area and subsequently the compensation costs for wildlife damage. The proposed approach can come in support of local and regional policies for the definitions of compensation for farmers. [less ▲]

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See detailTerrestrial photogrammetry: a non-destructive method for modelling irregularly shaped tropical tree trunks
Bauwens, Sébastien ULiege; Fayolle, Adeline ULiege; Gourlet-Fleury, Sylvie et al

in Methods in Ecology and Evolution (2016)

1. Irregularly shaped trees including trees with buttresses, flutes or stilt roots are frequent in tropical forests. The lack of an international standard tomeasure the diameter of such trees leads to ... [more ▼]

1. Irregularly shaped trees including trees with buttresses, flutes or stilt roots are frequent in tropical forests. The lack of an international standard tomeasure the diameter of such trees leads to high uncertainties in biomass estimation, tree growth and carbon budget monitoring. 2. In this study, we developed a new method based on terrestrial close-range photogrammetry for measuring andmodelling irregular stems. This approach is cheap and easy to implement in the field as it only requires a camera and a graduated rod. We validated the approach with destructive cross-sectionmeasurements along the stem of three buttressed trees. To demonstrate the broader utility of this method, we extended the validated approach to 43 additional trees belonging to two species: Celtis mildbraedii (Ulmaceae) and Entandophragma cylindricum (Meliaceae). Based on the three dimensional models, we computed shape indices for each tree, and we analysed the stem morphology of the two species. Finally, we analysed some standardized predictors for the estimation of above-ground biomass. 3. We found a high concordance between diameters derived from the photogrammetric process and destructive diameter measurements along the stem for the three calibration trees. We found that C. mildbraedii develop much stronger irregularities than E. cylindricum.We also identified a large intraspecific variation in trunk morphology for E. cylindricum. The basal area at 1 3 mheight (Darea130) seems to be amore robust predictor for biomass estimates (lowest Akaike information criterion and relative squared error) than diameter measured above buttresses (DAB) or diameter at breast height estimated from available taper model. Finally, Darea130 might be estimated with a good precision [root mean square error (RMSE) < 5%] with linear model based on the field measurements DABand the perimeter of the convex hull of the buttresses at 1 3 mheight (Dconvhull130). 4. In this study, we showed the high potential of the photogrammetry for measuring and modelling irregular stems. Photogrammetry could then be used as a non-destructivemeasurement tool to produce correction factors for standardizing the diameter of irregular stems at a reference height which is a key issue in tree growthmonitoring and biomass change estimation. [less ▲]

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See detailCharacterization of Forests with LiDAR Technology
Michez, Adrien ULiege; Bauwens, Sébastien ULiege; Bonnet, Stéphanie ULiege et al

in Baghdadi, Nicolas; Zribi, Mehrez (Eds.) Land Surface Remote Sensing in Agriculture and Forest (2016)

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See detailBack on Track... in 3D
Marchal, Antoine ULiege; Lejeune, Philippe ULiege; De Bruyn, Nico

Poster (2016, September 04)

Ecological monitoring provides basic information on population status and distribution that is crucial for conservation, research and management strategies. Studies using tracks are controversial due to ... [more ▼]

Ecological monitoring provides basic information on population status and distribution that is crucial for conservation, research and management strategies. Studies using tracks are controversial due to past misuses tainted with subjectivity. Advances in photogrammetry literally add another dimension to the recording techniques, and geometric morphometrics provides an appropriate approach for the study of track shape variation. Tracks are back on track in conservation! [less ▲]

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See detailForest Inventory with Terrestrial LiDAR: A Comparison of Static and Hand-Held Mobile Laser Scanning
Bauwens, Sébastien ULiege; Bartholomeus, Harm; Calders, Kim et al

in Forests (2016), 7(6), 127

The application of static terrestrial laser scanning (TLS) in forest inventories is becoming more effective. Nevertheless, the occlusion effect is still limiting the processing efficiency to extract ... [more ▼]

The application of static terrestrial laser scanning (TLS) in forest inventories is becoming more effective. Nevertheless, the occlusion effect is still limiting the processing efficiency to extract forest attributes. The use of a mobile laser scanner (MLS) would reduce this occlusion. In this study, we assessed and compared a hand-held mobile laser scanner (HMLS) with two TLS approaches (single scan: SS, and multi scan: MS) for the estimation of several forest parameters in a wide range of forest types and structures. We found that SS is competitive to extract the ground surface of forest plots, while MS gives the best result to describe the upper part of the canopy. The whole cross-section at 1.3 m height is scanned for 91% of the trees (DBH > 10 cm) with the HMLS leading to the best results for DBH estimates (bias of 0.08 cm and RMSE of 1.11 cm), compared to no fully-scanned trees for SS and 42% fully-scanned trees for MS. Irregularities, such as bark roughness and non-circular cross-section may explain the negative bias encountered for all of the scanning approaches. The success of using MLS in forests will allow for 3D structure acquisition on a larger scale and in a time-efficient manner. [less ▲]

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See detailApport des nuages de points LiDAR et photogrammétriques pour le monitoring de 12000 km de cours d’eau en Wallonie (Belgique)
Michez, Adrien ULiege; Piégay, Hervé; Desteucq, Olivier et al

Conference (2016, June 10)

Sous l’impulsion de son administration, la Wallonie a entamé un processus de révision complète des modalités de la gestion des cours d’eau, notamment à travers le projet des Programmes d’Actions sur les ... [more ▼]

Sous l’impulsion de son administration, la Wallonie a entamé un processus de révision complète des modalités de la gestion des cours d’eau, notamment à travers le projet des Programmes d’Actions sur les Rivières par une approche Intégrée et Sectorisée (PARIS). Les PARIS ont pour but l'intégration dans le temps et dans l’espace de l’ensemble des mesures de gestion spécifiques au linéaire des cours d'eau en fonction d'enjeux prioritaires identifiés à l’échelle d’unités de gestion homogènes, les secteurs (6185 secteurs de gestion de 2 km de long en moyenne). La mise en place et le suivi de ces plans de gestion impliquent de facto le développement d'outils de suivi efficaces, permettant d'établir les états des lieux pour la planification des actes de gestion et à terme, d'évaluer l'efficacité desdits plans de gestion. Ces opérations doivent se réaliser sur près de 12000 km de cours d’eau et de bandes riveraines associées sur une base objective et commune à l’ensemble des gestionnaires de cours d’eau. Des données fines de télédétection étant disponibles et acquises de manière régulière par l’administration wallonne, des solutions dérivées de ces sources de données permettront de répondre partiellement aux besoins réguliers en information des plans de gestion PARIS pour un budget réduit. Pour atteindre cet objectif, un protocole a été établi sur base de nuages points LiDAR (densité ≈ 1 point « sol » / m²) complétés par des nuages de points photogrammétriques dérivés des images individuelles des couvertures ortho du territoire. Ces données ont été utilisées afin de caractériser la structure spatiale des bandes riveraines associées à l’ensemble du réseau hydrographique wallon (> 12 000 km) à travers 6 paramètres. Ces paramètres peuvent être d’ordre hydromorphologique (hauteur des berges, largeur et sinuosité du lit mineur), ou décrire la structure des forêts riveraines (hauteur moyenne, continuité longitudinale et ombrage du lit mineur). Une évaluation des patrons spatiaux de ces différents paramètres en lien avec les caractéristiques des territoires wallons (occupation du sol, régions naturelles) peut être ainsi réalisée. Différentes formes de visualisations de l’information peuvent ainsi appuyer le processus décisionnel des gestionnaires, de l’échelle locale (secteurs d’une masse d’eau DCE - Directive ‘Cadre-Eau’) à l’échelle régionale (354 masse d’eau DCE). L’acquisition des données sur l’ensemble du territoire wallon (15000 km²) a été sous-traitée à différentes compagnies privées, pour des montants approximatifs de 17 et 10 € / km² respectivement pour la donnée LiDAR et ortho. Une plateforme en ligne a récemment été lancée par la Direction des Cours d’Eau Non-Navigables du Service Public de Wallonie (DCENN) en tant que support du projet de plans de gestion PARIS. Les paramètres extraits dans le cadre de ce projet seront prochainement intégrés au sein de cette plateforme permettant leur visualisation à différentes échelles ainsi que l’encodage des actions par les gestionnaires. [less ▲]

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Full Text
See detailNouvelles normes sylvicoles pour les peuplements purs équiennes d'épicéa et de douglas
Perin, Jérôme ULiege; Hebert, Jacques ULiege; Lejeune, Philippe ULiege et al

E-print/Working paper (2016)

Ces documents rassemblent les tables de production (version 2016) représentant les nouvelles normes sylvicoles recommandées pour les peuplements purs équiennes d'épicéa commun et de douglas. Un ensemble ... [more ▼]

Ces documents rassemblent les tables de production (version 2016) représentant les nouvelles normes sylvicoles recommandées pour les peuplements purs équiennes d'épicéa commun et de douglas. Un ensemble de 10 tables de production est présentée pour chaque essence, associant deux densités de plantation (2.5 x 2 m et 2 x 2 m) et 5 classes de productivité (0 à IV). [less ▲]

Detailed reference viewed: 384 (67 ULiège)