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Introduction The purpose of the present work is to create a tool able to simplify the analysis of atmospheric phenomena in lower atmosphere; with specific application to up-slope winds on sloping terrain and the evaporation of water vapor from the vegetation. Models of atmospheric processes occurring close to the ground and GIS display a point of c...
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A small body of knowledge exists on the root water uptake RWU and evapotranspiration in humid environments having a mixture of natural vegetative cover. In this paper, we assess the impacts of atmospheric conditions and land cover on RWU from a natural vegetative cover. An intensive field investigation was carried out to monitor water table fluctua...
Citations
... In general, 3D rasters can be used for development of new remotely sensed data processing techniques and subsequent landscape ecology methodologies and measures such as landscape indices or connectivity metrics. Specifically 3D rasters in GRASS GIS were used in past for modeling of evaporation processes in 3D [46]. ...
Background
Point clouds with increased point densities create new opportunities for analyzing landscape structure in 3D space. Taking advantage of these dense point clouds we have extended a 2D forest fragmentation index developed for regional scale analyses into a 3D index for analyzing vegetation structure at a much finer scale.
Methods
Based on the presence or absence of points in a 3D raster (voxel model) the 3D fragmentation index is used to evaluate the configuration of a cell’s 3D neighborhood resulting in fragmentation classes such as interior, edge, or patch. In order to incorporate 3D fragmentation into subsequent conventional 2D analyses, we developed a transformation of this 3D fragmentation index into a series of 2D rasters based on index classes.
Results
We applied this method to a point cloud obtained by airborne lidar capturing a suburban area with mixed forest cover. All processing and visualization was done in GRASS GIS, an open source, geospatial processing and remote sensing tool. The newly developed code is also publicly available and open source. The entire processing chain is available and executable through Docker for maximum reproducibility.
Conclusions
We demonstrated that this proposed index can be used to describe different types of vegetation structure making it a promising tool for remote sensing and landscape ecology. Finally, we suggest that processing point clouds using 3D raster methods including 3D raster algebra is as straightforward as using well-established 2D raster and image processing methods.
... Many natural processes are directly influenced by the incoming solar energy e.g. permafrost distribution [37], evapotranspiration (sum of evaporation and transpiration) [38] and hence it can be thought about integrating this approach in models simulating these processes. Nevertheless, many improvements can still be made (Section 5.) and are planned for future studies. ...
A relative height threshold is defined to separate potential roof points from the point cloud, followed by a segmentation of these points into homogeneous areas fulfilling the defined constraints of roof planes. The normal vector of each laser point is an excellent feature to decompose the point cloud into segments describing planar patches. An object-based error assessment is performed to determine the accuracy of the presented classification. It results in 94.4% completeness and 88.4% correctness. Once all roof planes are detected in the 3D point cloud, solar potential analysis is performed for each point. Shadowing effects of nearby objects are taken into account by calculating the horizon of each point within the point cloud. Effects of cloud cover are also considered by using data from a nearby meteorological station. As a result the annual sum of the direct and diffuse radiation for each roof plane is derived. The presented method uses the full 3D information for both feature extraction and solar potential analysis, which offers a number of new applications in fields where natural processes are influenced by the incoming solar radiation (e.g., evapotranspiration, distribution of permafrost). The presented method detected fully automatically a subset of 809 out of 1,071 roof planes where the arithmetic mean of the annual incoming solar radiation is more than 700 kWh/m(2).
... More specifically, geostatistical interpolation methods offer good alternatives for the estimation of climatic parameters, as precipitation, at unrecorded sites with good accuracy (Martínez-Cob, 1996;Goovaerts, 2000;Diodato & Michele, 2005). Moreover, there are several models which have been developed for the estimation of the topographically influenced incoming solar radiation (Hofierka, 1997;Hughes, 2000;Ciolli et al., 2002;Reuter et al., 2005). The accuracy of predictions largely depends on the spatial resolution of the DEM and in present, DEMs of even 1x1 m resolution can be purchased while DEM with 90x90m grid resolution -which is an adequate resolution for the study of vegetation's distribution at regional scales-are freely available (Reuter et al., 2007;Jarvis et al., 2008). ...
Die Analyse der Verbreitungsgrenzen der Baumarten ist essentiell bei der Einschätzung der Wirkungen von Klimaänderungen. Die vorliegende Arbeit untersucht die Trockengrenze der Buche (Fagus sylvatica L.) auf Kalkböden am Olymp in Griechenland. Die Ergebnisse sind wichtig für die Einschätzung der Standortsgerechtigkeit der Buche unter ähnlichen Klimabedingungen.
Die Analyse der Trockengrenze der Buche wurde an naturnahen Grenzbereichen („Ökotonen“) zwischen Buchen- und Kiefern-(Pinus nigra)-Wäldern durchgeführt. Standorts- und Vegetationsdaten wurden von 108 Probeflächen erhoben, die in 36 Dreiergruppen („Triplets“) quer zu den Ökotonen angeordnet waren und verschiedene Expositionen und Höhenstufen umfassten. Der Abstand zwischen den Probeflächen im Triplet betrug ca. 40 m. Für jede Probefläche wurden alle Gefäßpflanzenarten mit der LONDO-Skala aufgenommen, ebenso Standortsparameter, insbesondere des Wasserhaushalts (nutzbare Feldkapazität; aktuelle und potenzielle Evapotranspiration, Wasserdefizit, Niederschlag).
Die Bodenvegetation wurde mittels TWINSPAN klassifiziert, durch indirekte (non-metric multidimensional scaling) und direkte (CCA) Gradientenanalysen mit Umweltvariablen in Beziehung gebracht. Diskriminanzanalyse und „classification trees” zeigten die dominierenden Variablen auf, welche die Verbreitung der Waldtypen und somit die Trockengrenze der Buchenbestände bestimmten.
Ergebnis: Der dominante Gradient reicht von “trockenen” Probeflächen mit Kiefern hin zu „frischen“ Probeflächen mit Buchenbeständen. Die aktuelle Evapotranspiration und das Wasserdefizit erwiesen sich als die treibenden Faktoren für die Artenzusammensetzung. Somit müssen zur Einschätzung von Trockenheit edaphische und klimatische Komponenten von Trockenheit berücksichtigt werden. Buchenbestände finden sich am Olymp auf Standorten mit aktuellen Evapotranspirationsraten >276.5 mm, Kiefernbestände zumeist auf Standorten mit aktuellen Evapotranspirationsraten <276.5 mm und einem Wasserdefizit >312.5 mm für die 3 trockensten Monate (Juni bis August). Die Quantifizierung der Trockengrenze der Buche am Olymp ermöglicht verbesserte Vegetations-Standorts-Modelle und gibt Hinweise für künftige Waldbewirtschaftungen.
... Infact, the management of hetherogeneus data linked by their position is what GISs are about. The development of a model for local atmospheric study within a GIS environment has started some years ago, resulting in a local thermally driven slope winds model based on the 3D raster GRASS model [1], [2], [3]. This model evaluates wind velocity and (potential) temperature anomaly in a volume over a slope. ...
... A more detailed discussion of the determination of these heat fluxes can be found in [1], [2], [3], where references are provided. The evaluation of the the sensible heat flux Q H is essential for the estimation of temperature and wind velocity over the slope. ...
... where q is the specific humidity. The expressions for θ V and u can be derived by applying the same procedure above, but in addition to the heat budget condition of equation 1 the conservation of moisture flux F W must be imposed [2]. ...
A vector model has been setup to evaluate wind speed and direction for thermally driven slope winds. This model is based on an extension of the Prandtl model and uses the new GRASS 3D vector implemen-tation as well as its connection to external DBMS. This model follows the model for the raster approach to a local metereological model for the evaluation of temperature, wind speed and humidity [1], based on the 3D raster GRASS capability. The new vector implementation allows the evaluation of temperature, wind speed and direction on a set of irregular placed points, while the raster approach is constrained to use points on a regular grid. Moreover, all the attributes that are used as parameters in the model are managed through PostgreSQL and SQL queries. A new GRASS module has been written to evaluate the normal direction through a point in the 3D space, since all the model parameters depend on the distance from the surface along the normal direction. A comparison between the vector and the raster approach, in terms of implementation and use, is presented. Finally a synthetic and a real simulation and a comparison with the raster model results are reported.
... [48], re-design of r.hydro.casc2d [55], as well as new models such as evaporation over tilted slopes [41], or solar radiation r.sun [49]; ...
... (including option for computation of precipitation with influence of topography) [10]. Another examples are modeling of evaporation processes by r3.mapcalc [41] and 3D geology models [51]. Port of nviz to OpenGL [3] opened the use of GRASS visualization to non-SGI platforms as reflected for example in papers [65], [53], [40], [51]. ...
... GRASS is being applied in several new fields (besides its traditional environmental and land management), for example, in geology [51], [50]; coast and sea [61], [53], space [43], atmospheric [41], [42], real time hydrology [55]; linkages to other Open Source and Free Software projects such as gstat or R statistical software [2], [37] continue to rapidly expand and strengthen the power of Open Source and Free Software geospatial computing environment. ...
Introduction Over the past decade geoinformation field has evolved from a highly specialized niche to a technology with broad impact on society and its interaction with nature. Geographic Information Systems (GIS) applications now range from simple navigation to critical and extremely complex tasks, such as prediction and management of natural disasters. Due to the increased use of GPS, faster access to georeferenced data, expanding field of remote sensing and real-time monitoring, GIS technology is entering many new disciplines and industries and GIS is becoming a part of general computational infrastructure. It is therefore natural that geospatial tools are being developed also within the Open Source and Free Software community [60]. Several important trends can be identified in the current development of geospatial technology: modern, highly automated mapping and monitoring technologies produce massive amounts of spatiotemporal georeferenced data (e.g., LIDAR [39], [53], IFSARE,
Numerical simulation of atmospheric phenomena closely depending on interaction with ground requires a detailed representation of values of various fields of distributed land variables such as solar irradiance, local slope and exposition, land covering, underground nature and so on. In some cases it is convenient to integrate simple models simulating the phenomena above into a system for management of geographic information. However, the intrinsic 3D nature of these phenomena has been so far an obstacle to the implementation of suitable models, due to the impossibility of managing such data by means of the available Geographic Information Systems. The modules which have been recently made available in GRASS for management and treatment of 3D data allow the development of suitable algorithms by combination of both 2D and 3D data and modules. In the present work we show some preliminary results of a simulation of slope winds which develop along sloping valley side-walls due to ground heating or cooling. Simple classical parameterizations of wind and temperature profiles, obtained in the case of plain tilted slope (Prandtl, 1942; Defant, 1949), have been used along with distributed data over a 2D domain (incidence radiation, land nature and use, local slope from DTM, etc.) to evaluate a suitable energy balance at ground level and fields of meteorological variables such
The ability to manage and process fully three-dimensional information has only recently been made available for a few Geographical Information Systems (GIS). An example of integrated and complementary use of 2D and 3D GRASS modules for the evaluation and representation of thermally induced slope winds over complex terrain is presented. The analytic solution provided by Prandtl (1942) to evaluate wind velocity and (potential) temperature anomaly induced by either diurnal heating or nocturnal cooling on a constant angle slope is adopted to evaluate wind and temperature profiles at any point over both idealised and real complex terrain. As these quantities depend on the slope angle of the ground and on the distance from the slope surface suitable procedures are introduced to determine the coordinate n of a point in the 3D volume measured along the direction locally normal to the terrain surface. A new GRASS module has been developed to evaluate this quantity and to generate a 3D raster file where each cell is assigned the value of the cell on the surface belonging to the normal vector. The application of the algorithm implemented in
