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See detailIntroduction aux géotraitements dans l’environnement R
Lejeune, Philippe ULiege; Michez, Adrien ULiege

Learning material (2020)

Tutoriel d'initiation aux géotraitements dans l'environnement R

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See detailCan regional aerial images from orthophoto surveys produce high quality photogrammetric Canopy Height Model? A single tree approach in Western Europe
Michez, Adrien ULiege; Huylenbroeck, Léo ULiege; Bolyn, Corentin ULiege et al

in International Journal of Applied Earth Observation and Geoinformation (2020), 92

Forest monitoring tools are needed to promote effective and data driven forest management and forest policies. Remote sensing techniques can increase the speed and the cost-efficiency of the forest ... [more ▼]

Forest monitoring tools are needed to promote effective and data driven forest management and forest policies. Remote sensing techniques can increase the speed and the cost-efficiency of the forest monitoring as well as large scale mapping of forest attribute (wall-to-wall approach). Digital Aerial Photogrammetry (DAP) is a common cost-effective alternative to airborne laser scanning (ALS) which can be based on aerial photos routinely acquired for general base maps. DAP based on such pre-existing dataset can be a cost effective source of large scale 3D data. In the context of forest characterization, when a quality Digital Terrain Model (DTM) is available, DAP can produce photogrammetric Canopy Height Model (pCHM) which describes the tree canopy height. While this potential seems pretty obvious, few studies have investigated the quality of regional pCHM based on aerial stereo images acquired by standard official aerial surveys. Our study proposes to evaluate the quality of pCHM individual tree height estimates based on raw images acquired following such protocol using a reference filed-measured tree height database. To further ensure the replicability of the approach, the pCHM tree height estimates benchmarking only relied on public forest inventory (FI) information and the photogrammetric protocol was based on low-cost and widely used photogrammetric software. Moreover, our study investigates the relationship between the pCHM tree height estimates based on the neighboring forest parameter provided by the FI program. Our results highlight the good agreement of tree height estimates provided by pCHM using DAP with both field measured and ALS tree height data. In terms of tree height modeling, our pCHM approach reached similar results than the same modeling strategy applied to ALS tree height estimates. Our study also identified some of the drivers of the pCHM tree height estimate error and found forest parameters like tree size (diameter at breast height) and tree type (evergreenness/deciduousness) as well as the terrain topography (slope) to be of higher importance than image survey parameters like the variation of the overlap or the sunlight condition in our dataset. In combination with the pCHM tree height estimate, the terrain slope, the Diameter at Breast Height (DBH) and the evergreenness factor were used to fit a multivariate model predicting the field measured tree height. This model presented better performance than the model linking the pCHM estimates to the field tree height estimates in terms of r² (0.90 VS 0.87) and root mean square error (RMSE, 1.78 VS 2.01 m). Such aspects are poorly addressed in literature and further research should focus on how pCHM approaches could integrate them to improve forest characterization using DAP and pCHM. Our promising results can be used to encourage the use of regional aerial orthophoto surveys archive to produce large scale quality tree height data at very low additional costs, notably in the context of updating national forest inventory programs. [less ▲]

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See detailUsing remote sensing to characterize riparian vegetation: a review of available tools and perspectives for managers
Huylenbroeck, Léo ULiege; Laslier, Marianne; Dufour, Simon et al

in Journal of Environmental Management (2020), 267

Riparian vegetation is a central component of the hydrosystem. As such, it is often subject to management practices that aim to influence its ecological, hydraulic or hydrological functions. Remote ... [more ▼]

Riparian vegetation is a central component of the hydrosystem. As such, it is often subject to management practices that aim to influence its ecological, hydraulic or hydrological functions. Remote sensing has the potential to improve knowledge and management of riparian vegetation by providing cost-effective and spatially continuous data over wide extents. The objectives of this review were twofold: to provide an overview of the use of remote sensing in riparian vegetation studies and to discuss the transferability of remote sensing tools from scientists to managers. We systematically reviewed the scientific literature (428 articles) to identify the objectives and remote sensing data used to characterize riparian vegetation. Overall, results highlight a strong relationship between the tools used, the features of riparian vegetation extracted and the mapping extent. Very high-resolution data are rarely used for rivers longer than than 100 km, especially when mapping species composition. Multi-temporality is central in remote sensing riparian studies, but authors use only aerial photographs and relatively coarse resolution satellite images for diachronic analyses. Some remote sensing approaches have reached an operational level and are now used for management purposes. Overall, new opportunities will arise with the increased availability of very high-resolution data in understudied or data-scarce regions, for large extents and as time series. To transfer remote sensing approaches to riparian managers, we suggest mutualizing achievements by producting open-access and robust tools. These tools will then have to be adapted to each specific project, in collaboration with managers. [less ▲]

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See detailPlanetScope Radiometric Normalization and Sentinel-2 Super-Resolution (2.5 m): A Straightforward Spectral-Spatial Fusion of Multi-Satellite Multi-Sensor Images Using Residual Convolutional Neural Networks
Latte, Nicolas ULiege; Lejeune, Philippe ULiege

in Remote Sensing (2020), 12

Sentinel-2 (S2) imagery is used in many research areas and for diverse applications. Its spectral resolution and quality are high but its spatial resolutions, of at most 10 m, is not sufficient for fine ... [more ▼]

Sentinel-2 (S2) imagery is used in many research areas and for diverse applications. Its spectral resolution and quality are high but its spatial resolutions, of at most 10 m, is not sufficient for fine scale analysis. A novel method was thus proposed to super-resolve S2 imagery to 2.5 m. For a given S2 tile, the 10 S2 bands (four at 10 m and six at 20 m) were fused with additional images acquired at higher spatial resolution by the PlanetScope (PS) constellation. The radiometric inconsistencies between PS microsatellites were normalized. Radiometric normalization and super-resolution were achieved simultaneously using state-of–the-art super-resolution residual convolutional neural networks adapted to the particularities of S2 and PS imageries (including masks of clouds and shadows). The method is described in detail, from image selection and downloading to neural network architecture, training, and prediction. The quality was thoroughly assessed visually (photointerpretation) and quantitatively, confirming that the proposed method is highly spatially and spectrally accurate. The method is also robust and can be applied to S2 images acquired worldwide at any date. [less ▲]

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See detailCan water level stations be used for thermal assessment in aquatic ecosystem?
Georges, Blandine ULiege; Brostaux, Yves ULiege; Claessens, Hugues ULiege et al

in River Research and Applications (2020), 36(6), 960-973

Many studies focus on stream water temperature (WT) because it is considered a key ecological factor. However, few of them have investigated the use of WT data from water level monitoring networks, which ... [more ▼]

Many studies focus on stream water temperature (WT) because it is considered a key ecological factor. However, few of them have investigated the use of WT data from water level monitoring networks, which often measure WT as ancillary data. Our study was conducted in southern Belgium at a high temporal resolution with continuous data recorded at intervals of 10 min between 2012 and 2016 and large spatial scale greater than 16,000 km2. This study aimed to assess whether a regional water level network (140 stations) is reliable for continuous WT monitoring based on a Bland–Altman analysis with WT collected through a European monitoring network (Water Framework Directive). This study also investigates whether WT data acquired by water level stations can be used to perform both state‐of‐the‐art visualization of thermal regimes and spatio‐temporal queries for specific ecological monitoring. We found that the water level stations were reliable tools in recording continuous WT in the streams of the study area. The temperature difference between the two WT monitoring networks was −0.57°C on average. Our positive results promote the use of WT from water level stations in order to globally characterize the thermal regime of streams as well as to provide spatial or temporal information on this regime at high frequencies. As an example, our data showed the effectiveness for brown trout (Salmo trutta fario L.) in spatializing thermal risk areas related to the thermal requirement of this fish species; in 2015, 19% of stations located in brown trout fish zone recorded temperatures above 25°C. [less ▲]

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See detailUpscaling UAS Paradigm to UltraLight Aircrafts: A Low-Cost Multi-Sensors System for Large Scale Aerial Photogrammetry
Latte, Nicolas ULiege; Gaucher, Peter; Bolyn, Corentin ULiege et al

in Remote Sensing (2020), 12(8),

The use of unmanned aerial systems (UASs) has rapidly grown in many civil applications since the early 2010s. Nowadays, a large variety of reliable low-cost UAS sensors and controllers are available ... [more ▼]

The use of unmanned aerial systems (UASs) has rapidly grown in many civil applications since the early 2010s. Nowadays, a large variety of reliable low-cost UAS sensors and controllers are available. However, contrary to ultralight aircrafts (ULAs), UASs have a too small operational range to efficiently cover large areas. Flight regulations prevailing in many countries further reduced this operational range; in particular, the “within visual line of sight” rule. This study presents a new system for image acquisition and high-quality photogrammetry of large scale areas (>10 km²). It was developed by upscaling the UAS paradigm, i.e., low-cost sensors and controllers, little (or no) on-board active stabilization, and adequate structure from motion photogrammetry, to an ULA platform. Because the system is low-cost (good quality-price ratio of UAS technologies), multi-sensors (large variety of available UAS sensors) and versatile (high ULA operational flexibility and more lenient regulation than for other platforms), the possible applications are numerous in miscellaneous research domains. The system was described in detail and illustrated from the flight and images acquisition to the photogrammetric routine. The system was successfully used to acquire high resolution and high quality RGB and multispectral images, and produced precisely georeferenced digital elevation model (DEM) and orthophotomosaics for a forested area of 1200 ha. The system can potentially carry any type of sensors. The system compatibility with any sensor can be tested, in terms of image quality and flight plan, with the proposed method. This study also highlighted a major technical limitation of the low-cost thermal infrared cameras: the too high integration time with respect to the flight speed of most UASs and ULAs. By providing the complete information required for reproducing the system, the authors seek to encourage its implementation in different geographical locations and scientific contexts, as well as, its combination with other sensors, in particular, laser imaging detection and ranging (LiDAR) and hyperspectral. [less ▲]

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See detailHow Can Remote Sensing Help Monitor Tropical Moist Forest Degradation?—A Systematic Review
Dupuis, Chloé ULiege; Lejeune, Philippe ULiege; Michez, Adrien ULiege et al

in Remote Sensing (2020), 12(7), 1087

In the context of the climate and biodiversity crisis facing our planet, tropical forests playing a key role in global carbon flux and containing over half of Earth’s species are important to preserve ... [more ▼]

In the context of the climate and biodiversity crisis facing our planet, tropical forests playing a key role in global carbon flux and containing over half of Earth’s species are important to preserve. They are today threatened by deforestation but also by forest degradation, which is more difficult to study. Here, we performed a systematic review of studies on moist tropical forest degradation using remote sensing and fitting indicators of forest resilience to perturbations. Geographical repartition, spatial extent and temporal evolution were analyzed. Indicators of compositional, structural and regeneration criteria were noted as well as remote sensing indices and metrics used. Tropical moist forest degradation is not extensively studied especially in the Congo basin and in southeast Asia. Forest structure (i.e., canopy gaps, fragmentation and biomass) is the most widely and easily measured criteria with remote sensing, while composition and regeneration are more difficult to characterize. Mixing LiDAR/Radar and optical data shows good potential as well as very high-resolution satellite data. The awaited GEDI and BIOMASS satellites data will fill the actual gap to a large extent and provide accurate structural information. LiDAR and unmanned aerial vehicles (UAVs) form a good bridge between field and satellite data. While the performance of the LiDAR is no longer to be demonstrated, particular attention should be brought to the UAV that shows great potential and could be more easily used by local communities and stakeholders. [less ▲]

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See detailManaging the high variability of compressed sward heights to model grass growth on pastures using satellite images
Nickmilder, Charles ULiege; Soyeurt, Hélène ULiege; Dufrasne, Isabelle ULiege et al

Poster (2020, January 31)

ROADSTEP is a Walloon research program aiming to develop decision tools to help farmers in their daily herd monitoring on pastures. One of the aims is to develop a modelling tool to predict the ... [more ▼]

ROADSTEP is a Walloon research program aiming to develop decision tools to help farmers in their daily herd monitoring on pastures. One of the aims is to develop a modelling tool to predict the availability of pasture feeding based on satellite images, meteorological variables and soil characteristics. So, 72,975 compressed sward heights (CSH) have been measured on 30 parcels located in 3 farms using Jenquip EC20G platemeter in 2018 and 2019. CSH records (175 ± 53 mm) seemed to be normally distributed based on the low values of skewness (-1.96) and kurtosis (3.28). However, CSH gathered per parcel and per date showed a trend to unfit a normal distribution and seemed to be dependent on the location of the measurement spot on the parcel. Indeed, the observed kurtosis per parcel and test date were comprised between 0.64 and 27.40. Skewness values ranged from -4.39 to -1.38. These high kurtosis values highlight that CSH records were not normally distributed per parcel. Therefore, the current way to use an average CSH to represent a parcel is not the best choice as this value is not representative. This implies the need to adopt an unbiased approach that enables the comparison of CSH and other variables between dates. The chosen method consists in splitting the parcels in square sub-blocks. Each cell of this grid gathers all the climatic-soil related-satellite-median CSH data and is used as the unitary entity to train the predictive model of the biomass available in the pasture. [less ▲]

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See detailInvestigating stream water temperature in southern Belgium : environmental drivers and potential impact on a thermal sensitive species (Salmo trutta fario)
Georges, Blandine ULiege; Piégay, Hervé; Lejeune, Philippe ULiege et al

Poster (2020, January 31)

Stream water temperature (WT) is considered as a key ecological factor. Oxygen solubility, organic matter, decomposition rates,… are influenced by WT. Moreover, WT directly influences aquatic species by ... [more ▼]

Stream water temperature (WT) is considered as a key ecological factor. Oxygen solubility, organic matter, decomposition rates,… are influenced by WT. Moreover, WT directly influences aquatic species by interacting with the metabolism, growth and survival of species. In Wallonia (Southern Belgium, 16,000 km²), a water level monitoring network of about 140 stations also measures continuous WT taken at intervals of 10 minutes. Continuous monitoring allows detecting extreme thermal events generally harmful to aquatic organisms and time-limited because of high WT variability. The objectives of this study were : - To study WT evolution between 2012 and 2018, which are still underestimated due to the lack of regular and continuous monitoring over long periods; - To demonstrate the importance of having continuous temperature data for understanding and anticipating thermal damage to the aquatic ecosystem with the example of the brown trout (Salmo trutta fario L.); - To study the influence of land cover, topographical, hydromorphological and seasonal parameters on WT. The results showed a typical yearly sinusoidal evolution of the WT between 2012 and 2018. However, between years, remarkable thermal differences were observed reflecting the meteorological assessment established for the study period. Moreover, our data allowed us to map areas and target periods when temperatures too hot for brown trout are recorded. In addition to this essential information for the management of aquatic environments, the study of environmental factors has shown that shade has a strong impact on river temperature variability. This result provides an objective basis for conservatory management of riparian forest cover. [less ▲]

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See detailQuantifier les dimensions des houppiers à l’aide d’images aériennes à haute résolution pour estimer l’accroissement diamétrique des arbres dans les forêts d’Afrique centrale
Ndamiyehe Ncutirakiza, Jean-Baptiste; Lejeune, Philippe ULiege; Gourlet-Fleury, Sylvie et al

in Bois et Forêts des Tropiques (2020), 343

Characterising forest dynamics of a forest is essential to its management. Tree crowns are a key factor in these dynamics, but measuring them in tropical forests is not an easy matter. This study tested ... [more ▼]

Characterising forest dynamics of a forest is essential to its management. Tree crowns are a key factor in these dynamics, but measuring them in tropical forests is not an easy matter. This study tested the use of highresolution aerial imagery to estimate the tree diameter growth by incorporating detailed measurements of the detected tree crowns. Ortho-images at a resolution of 10 cm/pixel were captured by a fixed-wing drone over a 9 ha plot in the Yoko forest in the Democratic Republic of Congo. Inventories conducted on trees ≥ 10 cm diameter at breast height (DBH) in 2008 and 2016 provided access to a variety of tree dendrometric characteristics, including DBH and species temperament, and allowed the calculation of diameter increments. Mixed linear models were calibrated to predict diameter increment of 163 trees identified both on the ground and on the ortho-images, using variables quantified on the ground only and/or from variables measured from the orthoimages. From the aerial images, we were able to detect 23.4% of the trees with DBH ≥ 10 cm listed in the ground inventories, representing 75.1% of the stand’s aerial biomass. The probability of detecting the trees varied with their DBH, from 0.09 for trees with DBH < 30 cm to 0.97 for trees with DBH ≥ 60 cm. Predictions of diametric growth improved significantly when the variables quantified by remote sensing were added to the ground variables. The best models for estimating diameter increment include, in particular, a term characterising the size of tree crowns, which can only be measured by remote sensing. Of the variables determined by remote sensing, convex crown area was the most successfull in the models and therefore appears to be the most accurate variable to describe competition between tree crowns. These results open up possibilities to build new tools of data acquisition to support forest planning. [less ▲]

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See detailCartographie et caractérisation des arbres hors forêt à l’aide de la technologie LiDAR
Bolyn, Corentin ULiege; Latte, Nicolas ULiege; Fourbisseur, Anne et al

Article for general public (2020)

Il est aujourd’hui admis qu’une part importante de la ressource ligneuse se trouve en dehors de la forêt. Les « arbres hors forêt » ont un rôle important dans notre environnement grâce à leurs multiples ... [more ▼]

Il est aujourd’hui admis qu’une part importante de la ressource ligneuse se trouve en dehors de la forêt. Les « arbres hors forêt » ont un rôle important dans notre environnement grâce à leurs multiples fonctions : production de bois, préservation de la biodiversité, qualité paysagère… Bien que l’évolution récente des politiques environnementales tendent à leur donner plus d’importance, ils restent peu étudiés et ne font que rarement l’objet d’un inventaire ou d’un suivi à l’échelle régionale ou nationale. Face au besoin d’outils pour l’évaluation de cette ressource, une méthode de cartographie et de description des éléments arborés situés hors forêt a été développée. Elle repose sur l’utilisation de données LiDAR aérien au travers d’une série d’algorithmes intégrée dans une procédure automatique. Les éléments arborés de plus de 2 mètres de hauteur sont cartographiés avec une résolution de 1 mètre et catégorisés en cinq classes en fonction de leurs dimensions et de leur organisation spatiale. Les utilisations de cette couche cartographique sont nombreuses : calcul de statistiques, analyses spatiales, étude de la dynamique temporelle… À titre d’exemple, nous présentons les résultats obtenus sur trois sites : les communes rurales de Ohey et de Paliseul en Wallonie, et un périmètre regroupant douze communes françaises situées au Nord-Est de Valencienne. [less ▲]

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See detailAccuracy of tree stem circumference estimation using close range photogrammetry: Does point-based stem disk thickness matter?
Akpo, H. A.; Atindogbé, G.; Obiakara, M. C. et al

in Trees, Forests and People (2020), 2

There is an increase in the use of photogrammetric point clouds for tree attribute mensuration. Stem diameter and circumference can be estimated from point clouds using stem disks of varying thicknesses ... [more ▼]

There is an increase in the use of photogrammetric point clouds for tree attribute mensuration. Stem diameter and circumference can be estimated from point clouds using stem disks of varying thicknesses along the bole. However, there is a dearth of information on the effect of the thickness of point cloud-based stem disks on the accuracy of diameter and circumference estimations. In this study, we outlined a GIS-based procedure for analysing Structure from Motion-derived photogrammetric point clouds with a view to providing an optimal disk thickness for accurate circumference estimates. Geo-referenced point clouds were created from photographs of 30 trees belonging to five savanna species. For each tree, 20 horizontal stem disks, with increasing thicknesses of 1 to 20 mm were made at breast height using the open source QGIS software. The resulting cross-sections were manually delineated and digitised. The difference between reference (manually measured) and point cloud-based circumferences at breast height was expressed as mean absolute percent error (MAPE) and compared across tree species, size and disk thickness. We found significant effects of species identity, tree size and disk thickness on MAPE. A stem disk of 7 mm in thickness provided consistently lower MAPE values ( < 6%). This suggests that the accuracy of tree stem circumference estimations from photogrammetric point clouds depends on stem disk thickness. [less ▲]

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See detailCan Low-Cost Unmanned Aerial Systems Describe the Forage Quality Heterogeneity? Insight from a Timothy Pasture Case Study in Southern Belgium
Michez, Adrien ULiege; Lejeune, Philippe ULiege; David, Knoden et al

in Remote Sensing (2020), 12(10 1650),

Applied to grazing management, unmanned aerial systems (UASs) allow for the monitoring of vegetation at the level of each individual on the pasture while covering a significant area (>10 ha per flight ... [more ▼]

Applied to grazing management, unmanned aerial systems (UASs) allow for the monitoring of vegetation at the level of each individual on the pasture while covering a significant area (>10 ha per flight). Few studies have investigated the use of UASs to describe the forage quality in terms of nutritive value or chemical composition, while these parameters are essential in supporting the productive functions of animals and are known to change in space (i.e., sward species and structure) and time (i.e., sward phenology). Despite interest, these parameters are scarcely assessed by practitioners as they usually require important laboratory analyses. In this context, our study investigates the potential of off-the-shelf UAS systems in modeling essential parameters of pasture productivity in a precision livestock context: sward height, biomass, and forage quality. In order to develop a solution which is easily reproducible for the research community, we chose to avoid expensive solutions such as UAS LiDAR (light detection and ranging) or hyperspectral sensors, as well as comparing several UAS acquisition strategies (sensors and view angles). Despite their low cost, all tested strategies provide accurate height, biomass, and forage quality estimates of timothy pastures. Considering globally the three groups of parameters, the UAS strategy using the DJI Phantom 4 pro (Nadir view angle) provides the most satisfactory results. The UAS survey using the DJI Phantom 4 pro (Nadir view angle) provided R2 values of 0.48, 0.72, and 0.7, respectively, for individual sward height measurements, mean sward height, and sward biomass. In terms of forage quality modeling, this UAS survey strategy provides R² values ranging from 0.33 (Acid Detergent Lignin) to 0.85 (fodder units for dairy and beef cattle and fermentable organic matter). Even if their performances are of lower order than state-of-art techniques such as LiDAR for sward height or hyperspectral sensors (for biomass and forage quality modeling), the important trade-off in terms of costs between UAS LiDAR (>100,000 €) or hyperspectral sensors (>50,000 €) promotes the use of such low-cost UAS solutions. This is particularly true for sward height modeling and biomass monitoring, where our low-cost solutions provide more accurate results than state-of-the-art field approaches, such as rising plate meters, with a broader extent and a finer spatial grain. [less ▲]

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See detailImage data acquisition for estimating individual trees metrics: closer is better
Akpo, Hospice A.; Atindogbé, Gilbert; Obiakara, Maxwell C. et al

in Forests (2020), 11(1), 15

Background and Objectives: The recent use of Structure-from-Motion with Multi-View Stereo photogrammetry (SfM-MVS) in forestry has underscored its robustness in tree mensuration. This study evaluated the ... [more ▼]

Background and Objectives: The recent use of Structure-from-Motion with Multi-View Stereo photogrammetry (SfM-MVS) in forestry has underscored its robustness in tree mensuration. This study evaluated the di_erences in tree metrics resulting from various related SfM-MVS photogrammetric image acquisition scenarios. Materials and Methods: Scaled tri-dimensional models of 30 savanna trees belonging to five species were built from photographs acquired in a factorial design with shooting distance (d = 1, 2, 3, 4 and 5 m away from tree) and angular shift ( α = 15°, 30°, 45° and 60°; nested in d). Tree stem circumference at 1.3 m and bole volume were estimated using models resulting from each of the 20 scenarios/tree. Mean absolute percent error (MAPE) was computed for both metrics in order to compare the performance of each scenario in relation to reference data collected using a measuring tape. Results: An assessment of the e_ect of species identity (s), shooting distance and angular shift showed that photographic point cloud density was dependent on α and s, and optimal for 15° and 30°. MAPEs calculated on stem circumferences and volumes significantly di_ered with d and α , respectively. There was a significant interaction between α and s for both circumference and volume MAPEs, which varied widely (1.6 ± 0.4%–20.8 ± 23.7% and 2.0 ± 0.6%–36.5 ± 48.7% respectively), and were consistently lower for smaller values of d and α. Conclusion: The accuracy of photogrammetric estimation of individual tree attributes depended on image-capture approach. Acquiring images 2 m away and with 30° intervals around trees produced reliable estimates of stem circumference and bole volume. Research Highlights: This study indicates that the accuracy of photogrammetric estimations of individual tree attributes is species-dependent. Camera positions in relation to the subject substantially influence the level of uncertainty in measurements. [less ▲]

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See detailDynamique des populations d’azobé, Lophira alata Banks ex C. F. Gaertn., et implications pour sa gestion durable au Cameroun
Biwolé, Achille ULiege; Ouédraogo, Dakis-Yaoba; Betti, Jean Lagarde et al

in Bois et Forêts des Tropiques (2019), 342(novembre 2019), 55-68

L’impact de l’exploitation forestière sur le renouvellement du stock de bois d’oeuvre reste largement méconnu en Afrique centrale du fait du manque de données sur la dynamique des populations d’arbres ... [more ▼]

L’impact de l’exploitation forestière sur le renouvellement du stock de bois d’oeuvre reste largement méconnu en Afrique centrale du fait du manque de données sur la dynamique des populations d’arbres exploités. C’est en particulier le cas pour l’azobé, Lophira alata, un bois d’oeuvre de grande valeur commerciale. L’objectif de cette étude est double : quantifier l’effet du type forestier et de l’exploitation sur la croissance de l’azobé et simuler l’évolution du stock exploitable et du taux de reconstitution après exploitation. Nous avons effectué pendant trois ans un suivi annuel de la croissance et de la mortalité dans trois types forestiers au Cameroun : en forêt sempervirente, en forêt mixte et en forêt semi-caducifoliée. Le recrutement a été étudié uniquement en forêt mixte, sous deux conditions : en milieu exploité et non exploité. Nous avons calibré, avec ces données, un modèle matriciel de Usher. Douze scénarios d’exploitation ont été simulés en faisant varier le diamètre minimum d’exploitation de 60, 70 et 80 cm, et l’intensité de prélèvement des arbres de 100 à 40 %. La croissance de l’azobé est influencée à la fois par le type forestier et l’exploitation. Les arbres de forêt sempervirente ont une croissance plus faible jusqu’à 50 cm de diamètre, alors que la croissance maximale prédite pour ce type forestier est la plus élevée. L’exploitation a par ailleurs stimulé la croissance. Enfin, l’exploitation de l’azobé ne respecte pas le principe du rendement soutenu : ses taux de croissance à long terme varient entre 0,54 et 0,83 %. Pour garantir la durabilité de son exploitation au Cameroun, une sylviculture dynamisant la croissance des futurs arbres exploitables, ainsi que leur régénération, s’avère indispensable. [less ▲]

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See detailMalaria risk assessment and mapping using satellite imagery and boosted regression trees in the Peruvian Amazon
Solano Villarreal, Elisa Yoan ULiege; Valdivia, Walter; Pearcy, Morgan et al

in Scientific Reports (2019)

This is the first study to assess the risk of co-endemic Plasmodium vivax and Plasmodium falciparum transmission in the Peruvian Amazon using boosted regression tree (BRT) models based on social and ... [more ▼]

This is the first study to assess the risk of co-endemic Plasmodium vivax and Plasmodium falciparum transmission in the Peruvian Amazon using boosted regression tree (BRT) models based on social and environmental predictors derived from satellite imagery and data. Yearly cross-validated BRT models were created to discriminate high-risk (annual parasite index API > 10 cases/1000 people) and veryhigh-risk for malaria (API > 50 cases/1000 people) in 2766 georeferenced villages of Loreto department, between 2010–2017 as other parts in the article (graphs, tables, and texts). Predictors were cumulative annual rainfall, forest coverage, annual forest loss, annual mean land surface temperature, normalized difference vegetation index (NDVI), normalized difference water index (NDWI), shortest distance to rivers, time to populated villages, and population density. BRT models built with predictor data of a given year efficiently discriminated the malaria risk for that year in villages (area under the ROC curve (AUC) > 0.80), and most models also effectively predicted malaria risk in the following year. Cumulative rainfall, population density and time to populated villages were consistently the top three predictors for both P. vivax and P. falciparum incidence. Maps created using the BRT models characterize the spatial distribution of the malaria incidence in Loreto and should contribute to malaria-related decision making in the area. [less ▲]

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See detailAnalyse prospective de l'évolution de la ressource forestière wallonne
Perin, Jérôme ULiege; Lejeune, Philippe ULiege; Hebert, Jacques ULiege

Conference given outside the academic context (2019)

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See detailHarmonised projections of future forest resources in Europe
Vauhkonen, Jari; Berger, Ambros; Gschwantner, Thomas et al

in Annals of Forest Science (2019), 76:79

Abstract - Key message A dataset of forest resource projections in 23 European countries to 2040 has been prepared for forestrelated policy analysis and decision-making. Due to applying harmonised ... [more ▼]

Abstract - Key message A dataset of forest resource projections in 23 European countries to 2040 has been prepared for forestrelated policy analysis and decision-making. Due to applying harmonised definitions, while maintaining country-specific forestry practices, the projections should be usable from national to international levels. The dataset can be accessed at https://doi.org/10.5061/dryad.4t880qh. The associated metadata are available at https://metadata-afs.nancy.inra.fr/ geonetwork/srv/eng/catalog.search#/metadata/8f93e0d6-b524-43bd-bdb8-621ad5ae6fa9. [less ▲]

Detailed reference viewed: 33 (6 ULiège)
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See detailSupporting river management with UAV’s in the Provinces of Liège and Luxembourg
Huylenbroeck, Léo ULiege; Michez, Adrien ULiege; Lejeune, Philippe ULiege

Conference given outside the academic context (2019)

Detailed reference viewed: 24 (2 ULiège)