References of "Lejeune, Philippe"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailDiscrimination of deciduous tree species from time series of unmanned aerial system imagery
Lisein, Jonathan ULg; Michez, Adrien ULg; Claessens, Hugues ULg et al

in PLoS ONE (in press)

Technology advances can revolutionize Precision Forestry by providing accurate and fine forest information at tree level. This paper addresses the question of how and particularly when Unmanned Aerial ... [more ▼]

Technology advances can revolutionize Precision Forestry by providing accurate and fine forest information at tree level. This paper addresses the question of how and particularly when Unmanned Aerial System (UAS) should be used in order to efficiently discriminate deciduous tree species. A time series of high resolution UAS imagery was collected to cover the growing season from leaf flush to leaf fall. Full benefit was taken of the temporal resolution of UAS acquisition, one of the most promising features of small drones. The disparity in forest tree phenology is at the maximum during early spring and late autumn. But the phenology state that optimized the classification result is the one that minimizes the spectral variation within tree species groups and, at the same time, maximizes the phenologic differences between species. Sunlit tree crowns (5 deciduous species groups) were classified using a Random Forest approach for monotemporal, two-date and three-date combinations. The end of leaf flushing was the most efficient single-date time window. Multitemporal datasets definitely improve the overall classification accuracy. But single-date high resolution orthophotomosaics, acquired on optimal time-windows, result in a very good classification accuracy (overall out of bag error of 16%). [less ▲]

Detailed reference viewed: 46 (20 ULg)
Full Text
Peer Reviewed
See detailMapping of riparian invasive species with supervised classification of Unmanned Aerial System (UAS) imagery
Michez, Adrien ULg; Piégay, Hervé; Lisein, Jonathan ULg et al

in International Journal of Applied Earth Observation and Geoinformation (2016), 44

Riparian zones are key landscape features, representing the interface between terrestrial and aquatic ecosystems. Although they have been influenced by human activities for centuries, their degradation ... [more ▼]

Riparian zones are key landscape features, representing the interface between terrestrial and aquatic ecosystems. Although they have been influenced by human activities for centuries, their degradation has increased during the 20th century. Concomitant with (or as consequences of) these disturbances, the invasion of exotic species has increased throughout the world’s riparian zones. In our study, we propose a easily reproducible methodological framework to map three riparian invasive taxa using Unmanned Aerial Systems (UAS) imagery: Impatiens glandulifera Royle, Heracleum mantegazzianum Sommier and Levier, and Japanese knotweed (Fallopia sachalinensis (F. Schmidt Petrop.), Fallopia japonica (Houtt.) and hybrids). Based on visible and near-infrared UAS orthophoto, we derived simple spectral and texture image metrics computed at various scales of image segmentation (10,30, 45, 60 using eCognition software). Supervised classification based on the random forests algorithm was used to identify the most relevant variable (or combination of variables) derived from UAS imagery for mapping riparian invasive plant species. The models were built using 20% of the dataset, the rest of the dataset being used as a test set (80%). Except for H. mantegazzianum, the best results in terms of global accuracy were achieved with the finest scale of analysis (segmentation scale parameter = 10). The best values of overall accuracies reached 72%, 68%, and 97% for I. glandulifera, Japanese knotweed, and H. mantegazzianum respectively. In terms of selected metrics, simple spectral metrics (layer mean / camera brightness) were the most used. Our results also confirm the added value of texture metrics (GLCM derivatives) for mapping riparian invasive species. The results obtained for I. glandulifera and Japanese knotweed do not reach sufficient accuracies for operational applications. However, the results achieved for H. mantegazzianum are encouraging. The high accuracies values combined to relatively light model-inputs needed (delineation of a few umbels) make our approach a serious contender as a cost-effective tool to improve the field management of H. mantegazzianum. [less ▲]

Detailed reference viewed: 21 (4 ULg)
See detailVirtual plaster cast: digital 3D modelling of paws and tracks via photogrammetry
Marchal, Antoine ULg; De Bruyn, Nico; Lejeune, Philippe ULg

Conference (2015, July 17)

Detailed reference viewed: 17 (1 ULg)
Full Text
See detailGuide d'utilisation - Grille : Plugin de création de grilles d'échantillonnage pour le logiciel QGIS
Handerek, Daphné ULg; De Thier, Olivier ULg; Modave, Maxime et al

Learning material (2015)

Manuel d'utilisation du plugin grille pour QGIS.

Detailed reference viewed: 55 (7 ULg)
Full Text
See detailGrille : Plugin de création de grilles d'échantillonnage pour le logiciel QGIS
De Thier, Olivier ULg; Handerek, Daphné ULg; Modave, Maxime et al

Software (2015)

Le plugin Grille pour QGIS est destiné à définir et créer des grilles d’échantillonnage dans le cadre d’inventaires et de recensements appliqués à la gestion des ressources naturelles.

Detailed reference viewed: 55 (15 ULg)
Full Text
See detailForEstimator
Dedry, Laurent ULg; De Thier, Olivier ULg; Perin, Jérôme ULg et al

Software (2015)

ForEstimator est un plugin (une extension) QGIS qui permet d'estimer la hauteur dominante de peuplements résineux en Wallonie.

Detailed reference viewed: 89 (17 ULg)
Full Text
Peer Reviewed
See detailA novel procedure to measure shrinkage-free tree-rings from very large wood samples combining photogrammetry, high-resolution image processing, and GIS tools
Latte, Nicolas ULg; Beeckman, Hans; Bauwens, Sébastien ULg et al

in Dendrochronologia (2015), 34

We present a new procedure for wood sampling and tree-ring measurement that can be used for dendrochronological investigation on very large trees, specifically adapted for tropical rainforest species ... [more ▼]

We present a new procedure for wood sampling and tree-ring measurement that can be used for dendrochronological investigation on very large trees, specifically adapted for tropical rainforest species. This procedure takes advantage of the technological developments in computing, image processing, and geographic information systems (GIS) to overcome the technical limitations of the currently used methods. Two types of wood samples can be used (stem disks and/or bars) depending on tree diameter, and the difficulty of ring delineation and crossdating. Bars are an effective compromise between cores and disks. We developed an application combining several programs (Excel, R, ArcGIS, and MapWinGIS) in the Windows operating system for semi-automatic measurement of tree-rings from high-resolution images of the sanded cross-section. Using an innovative method to reverse the wood shrinkage resulting from the drying process, tree-ring measurement can be performed on shrinkage-free images, thus referring to the actual growth of the tree. [less ▲]

Detailed reference viewed: 33 (10 ULg)
Full Text
See detailDétection de l'érosion dans un bassin versant agricole par comparaison d'images multidates acquises par drone
Lisein, Jonathan ULg; Pineux, Nathalie ULg; Pierrot-Deseilligny, marc et al

Scientific conference (2015, March 26)

Detailed reference viewed: 36 (1 ULg)
Full Text
Peer Reviewed
See detailHow Tightly Linked Are Pericopsis elata (Fabaceae) Patches to Anthropogenic Disturbances in Southeastern Cameroon?
Bourland, Nils; Cerisier, François; Daïnou, Kasso ULg et al

in Forests (2015), 6(2), 293-310

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and ... [more ▼]

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and-burn agriculture since 3000–2000 BP (Before Present) could be the main driver of the persistence of light-demanding tree species. In order to examine anthropogenic factors in the persistence of such populations, our study focused on Pericopsis elata, an endangered clustered timber species. We used a multidisciplinary approach comprised of botanical, anthracological and archaeobotanical investigations to compare P. elata patches with surrounding stands of mixed forest vegetation (“out-zones”). Charcoal samples were found in both zones, but were significantly more abundant in the soils of patches. Eleven groups of taxa were identified from the charcoals, most of them also present in the current vegetation. Potsherds were detected only inside P. elata patches and at different soil depths, suggesting a long human presence from at least 2150 to 195 BP, as revealed by our charcoal radiocarbon dating. We conclude that current P. elata patches most likely result from shifting cultivation that occurred ca. two centuries ago. The implications of our findings for the dynamics and management of light-demanding tree species are discussed. [less ▲]

Detailed reference viewed: 11 (1 ULg)
Full Text
Peer Reviewed
See detailAre unmanned aircraft systems (UASs) the future of wildlife monitoring? A review of accomplishments and challenges
Linchant, Julie ULg; Lisein, Jonathan ULg; Semeki, Jean et al

in Mammal Review (2015)

1. Regular monitoring of animal populations must be established to ensure wildlife protection, especially when pressure on animals is high. The recent development of drones or unmanned aircraft systems ... [more ▼]

1. Regular monitoring of animal populations must be established to ensure wildlife protection, especially when pressure on animals is high. The recent development of drones or unmanned aircraft systems (UASs) opens new opportunities. UASs have several advantages, including providing data at high spatial and temporal resolution, providing systematic, permanent data, having low operational costs and being low-risk for the operators. However, UASs have some constraints, such as short flight endurance. 2. We reviewed studies in which wildlife populations were monitored by using drones, described accomplishments to date and evaluated the range of possibilities UASs offer to provide new perspectives in future research. 3. We focused on four main topics: 1) the available systems and sensors; 2) the types of survey plan and detection possibilities; 3) contributions towards antipoaching surveillance; and 4) legislation and ethics. 4. We found that small fixed-wing UASs are most commonly used because these aircraft provide a viable compromise between price, logistics and flight endurance. The sensors are typically electro-optic or infrared cameras, but there is the potential to develop and test new sensors. 5. Despite various flight plan possibilities, mostly classical line transects have been employed, and it would be of great interest to test new methods to adapt to the limitations of UASs. Detection of many species is possible, but statistical approaches are unavailable if valid inventories of large mammals are the purpose. 6. Contributions of UASs to anti-poaching surveillance are not yet well documented in the scientific literature, but initial studies indicate that this approach could make important contributions to conservation in the next few years. 7. Finally, we conclude that one of the main factors impeding the use of UASs is legislation. Restrictions in the use of airspace prevent researchers from testing all possibilities, and adaptations to the relevant legislation will be necessary in future. [less ▲]

Detailed reference viewed: 65 (22 ULg)
Full Text
Peer Reviewed
See detailAgent-based modelling of the spatial pattern of leisure visitation in forests: A case study in Wallonia, south Belgium
Li, Sen; Colson, Vincent; Lejeune, Philippe ULg et al

in Environmental Modelling & Software (2015), 71

The leisure use of forests is a fast growing sector in European tourism. The difficulties in monitoring real usage pattern have hindered communications in tourism, conservation and public health in ... [more ▼]

The leisure use of forests is a fast growing sector in European tourism. The difficulties in monitoring real usage pattern have hindered communications in tourism, conservation and public health in forested areas. In this study, we present an agent-based model to approximate forest visit patterns at the regional level, based on the visitor, residential and forest attributes. The model was then adapted locally for Wallonia, south Belgium, to predict the daily distribution of forest visits and visitor flows. The results suggest high visit rates in urban forests. In highly attractive forests that are distant from major cities, the visit rates may greatly respond to the visitor-level and environmental changes. Future empirical investigations are encouraged to build a cross-contextual understanding on visitors' decision-making mechanisms and to identify how these mechanisms may be influenced by environmental factors operating at different spatio-temporal levels. [less ▲]

Detailed reference viewed: 39 (3 ULg)
Full Text
See detailNew technologies in conservation: monitoring African wildlife with UAS
Linchant, Julie ULg; Semeki, Jean; Lejeune, Philippe ULg et al

Conference (2014, December 13)

In the vast protected areas of Africa, traditional wildlife surveys performed by plane or foot are logistically difficult to implement due to the lack of means and appropriate materials. Moreover, the ... [more ▼]

In the vast protected areas of Africa, traditional wildlife surveys performed by plane or foot are logistically difficult to implement due to the lack of means and appropriate materials. Moreover, the possibilities of encountering poachers in the field pose a serious risk to the monitoring teams. Over the last decade, civilian UAS (Unmanned Aerial Systems) boomed in natural resource monitoring. One of the biggest challenges of the UAS is to replace traditional wildlife censuses for the application of wildlife conservation. Parameters have to be approached in a different way than before. We performed test flights in the open savannah of the Garamba National Park during the wet season using the Falcon Unmanned UAS. Both photos (Sony Nex7, 24Mp) and videos, including thermal infrared videos (Tamarisk 640x480), have been used. Flight altitude ranged from 50 to 200m and pictures showed that animals can be effectively detected at 100m. We spotted elephants, hippopotamus and buffaloes as well as other smaller species such as hartebeests, kobs and warthogs. Thermal videos gave medium quality results during the day due to the heat but performed well during the night. The limited range and endurance of the UAS suggest a rethink of the usual census protocols. We therefore tested new flight plans in a rosette shape to take advantage of the higher points in the park, with transects having the length of the maximal range. Twelve transects of 10km can be covered in half a day with pictures covering a 15.6km² area. Human activities could also be detected. Pictures showed areas burned by poachers and the thermal infrared camera allows the detection of fires from a high altitude. Future developments need to be investigated such as automatic detection to review the huge amount of data collected and statistical methods must be adapted to those challenging situations. [less ▲]

Detailed reference viewed: 45 (13 ULg)
Full Text
Peer Reviewed
See detailForest inventory with Terrestrial LiDAR: what about Hand-Held Mobile LiDAR?
Bauwens, Sébastien ULg; Bartholomeus, Harm; Piboule, Alexandre et al

Conference (2014, November 05)

For a decade, studies of the application of static Terrestrial Laser Scanner (TLS) in plotwise forest inventories are giving more and more effective results. In spite of the improvements occurring in ... [more ▼]

For a decade, studies of the application of static Terrestrial Laser Scanner (TLS) in plotwise forest inventories are giving more and more effective results. In spite of the improvements occurring in processing scan data to extract forest attributes, the occlusion effect is still limiting the processing efficiency. A multi-scan approach is recommended to reduce this effect. However, such approach needs pre-scan preparations (setting up the plot, targets positioning), it requires data registration and it comes at a higher data collection cost. In this study we explore the potential of a Hand-held mobile LiDAR System (HMLS) as new LiDAR tool to scan forest plots. HMLS data are compared to static TLS data (single and multi-scan) in terms of data acquisition, registration time and quality of automatic DBH extraction. The low weight, small size of the instrument and no targets requirements reduce the time of pre-scan preparations to the time needed for single scan which is 6 times less than scanning a plot with 5 scans. The registration time depends of the time spent to scan the plot and it is of the same magnitude than single scan. The resulting point cloud of the HMLS is noisier than TLS point clouds. Nevertheless, error on DBH estimations is similar to scanning a plot with a TLS positioned at 5 locations. RMSE is higher than multi-scan and close to single scan for trees detected by the both LiDAR technologies. This first study exhibits the high potential of HMLS by its simple use, which needs only one operator while presenting similar results in automatic DBH extraction than static TLS. Technology and registering method improvements of this type of mobile LiDAR will reduce the noise of the point cloud, which might reduce the DBH RMSE. [less ▲]

Detailed reference viewed: 93 (19 ULg)
Full Text
See detailHow to survey your hippos night and day? Follow them in bed with drones!
Linchant, Julie ULg; Lejeune, Philippe ULg; Vermeulen, Cédric ULg

Scientific conference (2014, October 20)

Detailed reference viewed: 48 (5 ULg)
Full Text
Peer Reviewed
See detailSeasonal variations of wild boar Sus scrofa distribution in agricultural landscapes: a species distribution modelling approach
Morelle, Kevin ULg; Lejeune, Philippe ULg

in European Journal of Wildlife Research (2014)

Seasonal changes in the distribution of animals can have an important impact on the ecosystem. In agricultural landscapes, the seasonal movement of the wild boar Sus scrofa towards field crops often ... [more ▼]

Seasonal changes in the distribution of animals can have an important impact on the ecosystem. In agricultural landscapes, the seasonal movement of the wild boar Sus scrofa towards field crops often results in damages and makes control of the population difficult. The plasticity of the species to cope with different habitats is largely proven, but the environmental and human drivers of this seasonal habitat shift at the population scale remain largely unknown. Using MaxEnt and two seasonally distinct presence datasets, we contrasted the distribution of wild boar in southern Belgium during the growing and hunting seasons to (i) analyse seasonal drivers of the distribution and (ii) forecast the potential spread of the species north to its current distribution. We demonstrated that during the growing season, wild boar range almost double, owing to the cover and food provided by agricultural areas, thereby enhancing the movement and spread of the species. We found that the seasonal distribution of wild boar in agricultural lands is mostly influenced by the search for cover and food provided alternatively by forest and field crops. Interestingly, it seems that this search for cover operates under the constraint of a threshold distance. Our results indeed reveal an increased probability of presence not only in the vicinity of forests but also above a threshold distance of 865 m from the forest edge, suggesting that wild boar can overcome the dependence to forest cover. The forecast distribution of wild boar highlighted a potential increase of the current range into suitable habitat between 63 and 168 km2. To counteract the potential spread of the species into agricultural habitats and the consecutive damages, we insist on the need for the development of integrated management strategies, combining land use spatial configuration and wild boar spatial behaviour. [less ▲]

Detailed reference viewed: 38 (18 ULg)
Full Text
See detailI know what you did last summer - High resolution mapping of wild boar damages with drones
Michez, Adrien ULg; Morelle, Kevin ULg; Lehaire, François ULg et al

Poster (2014, September 01)

Wild boar ability to cause important damages to agricultural lands is not anymore to be demonstrated. These damages often raise conflicts between farmers and hunters due to the associated economic losses ... [more ▼]

Wild boar ability to cause important damages to agricultural lands is not anymore to be demonstrated. These damages often raise conflicts between farmers and hunters due to the associated economic losses. Objective and accurate method for real impact assessment of losses suffered by farmers is thus needed. Currently,in Wallonia damage assessment is performed from the ground by experts, asked to evaluate precisely the area impacted. This task is time and man power consuming. Moreover, damaged areas are often large and consequently, sampling is mandatory and can induce accuracy issues. Recent development of unmanned aerial vehicle (UAV / drone) toghether with lower cost and better accessibility for civil society and scientific community, makes now possible the use of this technology for wildlife researches. Through photogrammetric 3D reconstruction of the field crop, UAV can allow to objectively and precisely measure the area impacted by wild boar damages. In a context of increasing issues caused by wild boar to agriculture, and the need for stakeholders for accurate impact assessment, we tested an innovative approach to estimate more effectively the area impacted by wild boar. [less ▲]

Detailed reference viewed: 128 (15 ULg)