1,721,093 research outputs found
Valutazione degli effetti di eventi naturali disastrosi in zone boschive mediante acquisizioni LiDAR aeree e multi-temporali
Full text linkQuesto studio presenta un metodo di segmentazione automatica di nuvole di punti multi-temporali in zone boschive attraverso l’identificazione degli alberi e la localizzazione delle specie abbattute
A comparison of tree segmentation methods using very high density airborne laser scanner data
Full text linkAbstract. Developments of LiDAR technology are decreasing the unit cost per single point (e.g. single-photo counting). This brings to the possibility of future LiDAR datasets having very dense point clouds. In this work, we process a very dense point cloud (~200 points per square meter), using three different methods for segmenting single trees and extracting tree positions and other metrics of interest in forestry, such as tree height distribution and canopy area distribution. The three algorithms are tested at decreasing densities, up to a lowest density of ~5 point per square meter. Accuracy assessment is done using Kappa, recall, precision and F-Score metrics comparing results with tree positions from groundtruth measurements in six ground plots where tree positions and heights were surveyed manually. Results show that one method provides better Kappa and recall accuracy results for all cases, and that different point densities, in the range used in this study, do not affect accuracy significantly. Processing time is also considered; the method with better accuracy is several times slower than the other two methods and increases exponentially with point density. Best performer gave Kappa = 0.7. The implications of metrics for determining the accuracy of results of point positions’ detection is reported. Motives for the different performances of the three methods is discussed and further research direction is proposed.
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An automatic individual tree 3D change detection method for allometric parameters estimation in mixed uneven-aged forest stands from ALS data
Full text linkForests play a central role in the management of the Earth’s climate. Airborne laser scanning (ALS) technologies facilitate the monitoring of large and impassable areas and can be used to monitor the 3D structure of forests. While the ALS-based forest measures have been studied in depth, 3D change detection in forests is still a subject of little attention in the literature due to the challenges introduced by comparing point cloud pairs. In this study, we propose an innovative methodology to (i) automatically perform a 3D change detection of forests on an individual tree level(ii) estimate tree parameters with allometric equationsand (iii) perform an assessment of the aboveground biomass (AGB) variation over time. The area in which the tests were carried out was hit by an ice storm that occurred in the time interval between the two LiDAR acquisitionsfurthermore, field measurements were carried out and used to validate the results. The single-tree segmentation of the point clouds was automatically performed with a local maxima algorithm to detect the treetop, and a decision tree method to define the individual crowns around the local maxima. The multitemporal comparison of the point clouds was based on the identification of single trees, which were matched when there was a correlation between the position of the treetops. For each tree, the DBH (diameter at breast height) and the AGB were also estimated using allometric equations. The results are promising and allowed us to identify the uprooted trees and estimate that about 40% of the AGB of the area under examination had been destroyed, with an RMSE over the estimation ranging between 4% and 21% in four scenarios
Using airborne LiDAR to quantify changes in forest structure following an ice storm disturbance and subsequent salvage logging
Full text linkIce storms are common disturbance agents in temperate forests, often causing complex damage by partially destroying tree crowns. These irregular damage patterns pose challenges in production forests. Post-disturbance management decisions, such as salvage logging, are typically based on hastily collected field data, which is costly, time-consuming, and often fails to capture damage heterogeneity. Remote sensing offers a practical alternative. In 2014, a severe ice storm damaged mixed forests across the northern Dinaric Mountains. We used multitemporal high-density Airborne Laser Scanning data to validate a procedure for quantifying ice storm damage in stands dominated by Norway spruce, silver fir and European beech, using field data as a reference. LiDAR-derived leaf area density profiles and voxel-based biomass loss estimates effectively reflected field-observed patterns. Methods based on individual-tree segmentation underestimated post-disturbance tree density reductions, but basal area and volume loss estimates aligned closely with field measurements, even at low point densities. These methods offer a scalable approach to damage assessment and improve understanding of the spatial variability of ice storm impacts. They also hold considerable promise for land managers with access to regional bitemporal LiDAR datasets
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Analysis of landslides in the area of Lendavske gorice
Full text linkZemeljski plazovi so naraven pojav, ki pomembno vpliva na oblikovanje zemeljskega površja in se v Sloveniji pojavljajo pogosto, predvsem na območjih, kjer prevladujejo gričevja in hribovja. V sklopu diplomske naloge smo raziskali zemeljske plazove na območju Lendavskih goric, SV Slovenija. V sklopu terenskega dela smo popisali 58 zemeljskih plazov. Največ plazov je posledica obilnih padavin v kombinaciji z antropogenim dejavnikom. V največ primerih so se zemeljski plazovi pojavili kot hipni zdrs zemljine. Pred sprožitvijo plazu je prevladovala izbočena oblika terena. Na mestu odloma prevladujejo nakloni med 21 in 40 °. Prevladujejo plitvi zemeljski plazovi, večina pa jih je sanirana.Landslides are a natural phenomenon that has a significant impact on the formation of the landscape and occur frequently in Slovenia, especially in areas dominated by hills. Within the framework of the diploma thesis, we investigated landslides in the area of Lendavske gorice, NE Slovenia. During the fieldwork, we surveyed 58 landslides. Most landslides are triggered due to heavy rainfall, while anthropogenic factors also have important role. In most cases, landslides have occurred as a sudden slip of the earth, mainly on the slopes with convex shape and 21 and 40 ° of slope. Shallow landslides are prevalent and most of them are stabilised
Torrential control of Dovški potok above Dovje: a case study
No full textVarovalna vloga gozdov je ključna, zlasti ob neizogibnih podnebnih spremembah, ki v alpskem svetu še povečujejo tveganje za hudourniške procese. Za analizo vpliva veliko površinskih motenj na pretok in hudourniške procese smo izbrali Dovški potok na južnem pobočju Karavank, kjer so bili gozdovi v zadnjih desetih letih močno poškodovani. Z uporabo Kresnikove metode in hidrološkega modela ZEMOKOST smo določili pet scenarijev stanja gozda in ocenili različne razplete padavinskih dogodkov. Po enačbi Kresnik je stoletni pretok Dovškega potoka Q100 = 5,8 m³/s, medtem ko je bil leta 1961 izračunan na Q100 = 6,0 m³/s. Z modelom ZEMOKOST smo za različne scenarije dobili različne rezultate. Leta 2015, pred vplivom ujm, je bil Q100 = 3,6 m³/s in se je zgodil 45 minut po začetku padavin. Leta 2019, po ujmah, pa je Q100 narasel na 4,9 m³/s in se pojavil 39 minut po začetku padavin. Analiza hidravlične prevodnosti obstoječe hudourniške ureditve je pokazala, da ta ni več primerna glede na povečanje pretoka. Poleg tega smo na podlagi terenskih raziskav ugotovili, da erozijski drobir na območju predstavlja nevarnost za nastanek drobirskih in blatnih tokov, kar bi lahko ogrozilo vas Dovje.The protective role of forests is crucial, especially in the face of unavoidable climate change, which increases the risk of torrential processes in the alpine environment. To analyse the effects of large forest disturbances on runoff and torrential processes, we chose the Dovski potok on the southern slope of the Karawanken Mountains, where forests have been severely damaged in the last decade. Using the Kresnik method and the hydrological model ZEMOKOST, five scenarios for the state of the forests were determined and different scenarios of precipitation events were evaluated. According to the Kresnik equation, the 100-year discharge of the Dovski potok is Q100 = 5.8 m³/s, whereas in 1961 it was calculated as Q100 = 6.0 m³/s. The ZEMOKOST model provided different results for the different scenarios. In 2015, before the disturbances, the Q100 = 3.6 m³/s and occurred 45 minutes after the onset of the rainfall. In 2019, after the storms, Q100 increased to 4.9 m³/s and occurred 39 minutes after the onset of rainfall. Analysis of the hydraulic conductivity of the existing dams has shown that it is no longer sufficient to cope with the increase in runoff. In addition, on-site investigations have shown that the erosion debris deposits in the area harbour the risk of debris flows and mudslides that could endanger the village of Dovje
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