Consequence of DTM Precision for Flood Hazard Mapping: A Case Study in SW Finland

Spatial information on floods, which includes inundation maps and estimations of flood damage are essential tools for the creation of effective plans for both flood protection and mitigation. In flood modelling, the accuracy of the model geometry used has a remarkable impact upon flood mapping. Therefore, in this study, flood hazard mapping was undertaken with two existing DTM (digital terrain model) products and a high-precision LiDAR-based DTM. Their characteristics were evaluated with respect to flood hazard mapping. An accuracy assessment of these digital terrain models and their applicability for one-dimensional flood inundation mapping clearly showed that LiDAR DTM topography was the most applicable. Although the 10×10 m DTM from the Finnish National Land Survey could be utilised to show where flooding might occur for very coarse flood mapping surveys, these were not suitable for more exact estimations of flood boundaries. Nevertheless, some inaccuracies in riverbank topography were also found using the LiDAR-DTM. Hence, to study detailed hydrological processes such as short-term channel dynamics, this particular DTM could be further improved by additional data

Council in war : civilocracy, order and local organisation in daraya during the Syrian War

While scholars have focused on rebel governance in Syria and elsewhere, other forms of governance have been neglected. This article explores the local council established in the rebel-held city of Daraya, Syria. It informs the fields of rebel governance and civil resistance, specifically wartime order, during civil wars and proposes that the forms and practices of local governance in Daraya exhibited a type of governance best labelled as ‘civilocracy’. In contrast to councils in other opposition-held parts of Syria, the council was established and led by civilians who welcomed rebels to work with them. Based on findings from in-depth, semi-structured interviews with former council members, the article finds that four factors were crucial for this form of governance to emerge and to endure. Key wartime events – a massacre and a siege –, earlier experiences of nonviolent activists, local ties, and the creation of a military office created a space for the maintenance of civil-led order. Daraya offers a fascinating example of how community’s norms affected how rebel governance was created and maintained. This research introduces a new concept to explain wartime order and encourages researchers to find causal explanations for the emergence of this particular governance form in other conflicts.Peer reviewe

Laser scanning applications in fluvial studies

Peer reviewe

Intelligent open data 3D maps in a collaborative virtual world

Three-dimensional (3D) maps have many potential applications, such as navigation and urban planning. In this article, we present the use of a 3D virtual world platform Meshmoon to create intelligent open data 3D maps. A processing method is developed to enable the generation of 3D virtual environments from the open data of the National Land Survey of Finland. The article combines the elements needed in contemporary smart city concepts, such as the connection between attribute information and 3D objects, and the creation of collaborative virtual worlds from open data. By using our 3D virtual world platform, it is possible to create up-to-date, collaborative 3D virtual models, which are automatically updated on all viewers. In the scenes, all users are able to interact with the model, and with each other. With the developed processing methods, the creation of virtual world scenes was partially automated for collaboration activities.Peer reviewe

Automated 3D scene reconstruction from open geospatial data sources: airborne laser scanning and a 2D topographic database

Open geospatial data sources provide opportunities for low cost 3D scene reconstruction. In this study, based on a sparse airborne laser scanning (ALS) point cloud (0.8 points/m2) obtained from open source databases, a building reconstruction pipeline for CAD building models was developed. The pipeline includes voxel-based roof patch segmentation, extraction of the key-points representing the roof patch outline, step edge identification and adjustment, and CAD building model generation. The advantages of our method lie in generating CAD building models without the step of enforcing the edges to be parallel or building regularization. Furthermore, although it has been challenging to use sparse datasets for 3D building reconstruction, our result demonstrates the great potential in such applications. In this paper, we also investigated the applicability of open geospatial datasets for 3D road detection and reconstruction. Road central lines were acquired from an open source 2D topographic database. ALS data were utilized to obtain the height and width of the road. A constrained search method (CSM) was developed for road width detection. The CSM method was conducted by splitting a given road into patches according to height and direction criteria. The road edges were detected patch by patch. The road width was determined by the average distance from the edge points to the central line. As a result, 3D roads were reconstructed from ALS and a topographic database

Comparing accuracy of airborne laser scanning and TerraSAR-X radar images in the estimation of plot-level forest variables

Peer reviewe

Multisource Point Clouds, Point Simplification and Surface Reconstruction

As data acquisition technology continues to advance, the improvement and upgrade of the algorithms for surface reconstruction are required. In this paper, we utilized multiple terrestrial Light Detection And Ranging (Lidar) systems to acquire point clouds with different levels of complexity, namely dynamic and rigid targets for surface reconstruction. We propose a robust and effective method to obtain simplified and uniform resample points for surface reconstruction. The method was evaluated. A point reduction of up to 99.371% with a standard deviation of 0.2 cm was achieved. In addition, well-known surface reconstruction methods, i.e., Alpha shapes, Screened Poisson reconstruction (SPR), the Crust, and Algebraic point set surfaces (APSS Marching Cubes), were utilized for object reconstruction. We evaluated the benefits in exploiting simplified and uniform points, as well as different density points, for surface reconstruction. These reconstruction methods and their capacities in handling data imperfections were analyzed and discussed. The findings are that (i) the capacity of surface reconstruction in dealing with diverse objects needs to be improved; (ii) when the number of points reaches the level of millions (e.g., approximately five million points in our data), point simplification is necessary, as otherwise, the reconstruction methods might fail; (iii) for some reconstruction methods, the number of input points is proportional to the number of output meshes; but a few methods are in the opposite; (iv) all reconstruction methods are beneficial from the reduction of running time; and (v) a balance between the geometric details and the level of smoothing is needed. Some methods produce detailed and accurate geometry, but their capacity to deal with data imperfection is poor, while some other methods exhibit the opposite characteristics

Yksityiskohtaisen metsävaratiedon tuottaminen – kohti täsmämetsätaloutta?

Tieteen tori: Yksityiskohtainen metsävaratiet

Retrieval of Forest Aboveground Biomass and Stem Volume with Airborne Scanning LiDAR

Airborne scanning LiDAR is a promising technique for efficient and accuratebiomass mapping due to its capacity for direct measurement of the three-dimensionalstructure of vegetation. A combination of individual tree detection (ITD) and an area-basedapproach (ABA) introduced in Vastaranta et al. [1] to map forest aboveground biomass(AGB) and stem volume (VOL) was investigated. The main objective of this study was totest the usability and accuracy of LiDAR in biomass mapping. The nearest neighbourmethod was used in the ABA imputations and the accuracy of the biomass estimation wasevaluated in the Finland, where single tree-level biomass models are available. The relativeroot-mean-squared errors (RMSEs) in plot-level AGB and VOL imputation were 24.9%and 26.4% when field measurements were used in training the ABA. When ITDmeasurements were used in training, the respective accuracies ranged between 28.5%–34.9%and 29.2%–34.0%. Overall, the results show that accurate plot-level AGB estimates can beachieved with the ABA. The reduction of bias in ABA estimates in AGB and VOL wasencouraging when visually corrected ITD (ITDvisual) was used in training. We conclude that itis not feasible to use ITDvisual in wall-to-wall forest biomass inventory, but it could provide acost-efficient application for acquiring training data for ABA in forest biomass mapping.JRC.H.3-Forest Resources and Climat