Adrien Michez

Discrimination of Deciduous Tree Species from Time Series of Unmanned Aerial System Imagery

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. The goal of this research is to determine when is the best time window to achieve an optimal species discrimination. 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%).

Characterization of riparian zones in wallonia (belgium) from local to regional scale using aerial lidar data and photogrammetric DSM

The present study proposes an innovative approach to automatically extract riparian zone characteristics in order to assess its quality, from pre-determined river management reaches (1-3 km long) to regional scale (ca. 13,000 km for 1,000 management sectors). The aim of this remotely sensed monitoring is to improve river and riparian zone management and planning by providing some key information for river managers. The methodology was developed based on two watersheds covering approximately 500 km of river network (ca. 200 management sectors). The riparian zone quality is evaluated through various indicators of its ecological integrity (e.g., longitudinal continuity of riparian forest, mean vegetation height and relative standard deviation), hydromorphological quality and physical settings (e.g., flow channel extent, floodplain width, channel sinuosity). The physical characteristics of the riparian zone are mainly extracted from a high quality Digital Terrain Model (derived from ALS data), while the attributes of the riparian forest are derived from a hybrid Canopy Height Model (photogrammetric Digital Surface Model - Lidar derived DTM). This first research is exclusively based on data which are available at the regional scale (170,000 km 2 ) to develop automated tools to implement the methodology to the whole Walloon river network (13,000 km) before 2015 with an update frequency of three years (photogrammetric DSM survey frequency). Moreover, our approach is based on a photogrammetric Digital Surface Model which is derived from raw images of an orthophoto coverage. As most European countries are regularly covered by orthophoto surveys, our approach is widely replicable in countries where a quality DTM is available.

Forest cover correlates with good biological water quality. Insights from a regional study (Wallonia, Belgium)

Forested catchments are generally assumed to provide higher quality water in opposition to agricultural and urban catchments. However, this should be tested in various ecological contexts and through the study of multiple variables describing water quality. Indeed, interactions between ecological variables, multiple land use and land cover (LULC) types, and water quality variables render the relationship between forest cover and water quality highly complex. Furthermore, the question of the scale at which land use within stream catchments most influences stream water quality and ecosystem health remains only partially answered. This paper quantifies, at the regional scale and across five natural ecoregions of Wallonia (Belgium), the forest cover effect on biological water quality indices (based on diatoms and macroinvertebrates) at the riparian and catchment scales. Main results show that forest cover - considered alone - explains around one third of the biological water quality at the regional scale and from 15 to 70% depending on the ecoregion studied. Forest cover is systematically positively correlated with higher biological water quality. When removing spatial, local morphological variations, or population density effect, forest cover still accounts for over 10% of the total biological water quality variation. Partitioning variance shows that physico-chemical water quality is one of the main drivers of biological water quality and that anthropogenic pressures often explain an important part of it (shared or not with forest cover). The proportion of forest cover in each catchment at the regional scale and across all ecoregions but the Loam region is more positively correlated with high water quality than when considering the proportion of forest cover in the riparian zones only. This suggests that catchment-wide impacts and a fortiori catchment-wide protection measures are the main drivers of river ecological water quality. However, distinctive results from the agricultural and highly human impacted Loam region show that riparian forests are positively linked to water quality and should therefore be preserved.

Characterization of Forests with LiDAR Technology

Abstract: Forest surfaces on a global scale represent one-third of the world land area. Human civilizations have always interacted closely with these ecosystems, notably through the broad range of environmental services that they provide: protection of water resources, soil protection, mitigation of the excesses of local climate, reduction of impacts of gas emissions, and conservation of natural habitat and biodiversity. Apart from these environmental services, forests are also of interest to the social life of these civilizations, especially through economic and recreational functioning, as well as their cultural dimension. This interest in forest ecosystems results, in particular, in a desire to monitor or even control them. In the 20th Century, the advent of aerial and satellite imagery revolutionized the traditional image of the forestry officer, patiently counting and measuring his trees on the ground.