While CO2 emissions of cities are widely discussed, carbon storage in urban vegetation has been rarely empirically analyzed. Remotely sensed data offer considerable benefits for addressing this lack ...of information. The aim of this paper is to develop and apply an approach that combines airborne LiDAR and QuickBird to assess the carbon stored in urban trees of Berlin, Germany, and to identify differences between urban structure types. For a transect in the city, dendrometric parameters were first derived to estimate individual tree stem diameter and carbon storage with allometric equations. Field survey data were used for validation. Then, the individual tree carbon storage was aggregated at the level of urban structure types and the distribution of carbon storage was analysed. Finally, the results were extrapolated to the entire urban area. High accuracies of the detected tree locations were reached with 65.30% for all trees and 80.1% for dominant trees. The total carbon storage of the study area was 20,964.40 t ( sigma = 15,550.11 t). Its carbon density equaled 13.70 t/ha. A general center-to-periphery increase in carbon storage was identified along the transect. Our approach methods can be used by scientists and decision-makers to gain an empirical basis for the comparison of carbon storage capacities between cities and their subunits to develop adaption and mitigation strategies against climate change.
Vegetation provides important functions and services in urban areas, and vegetation heights divided into vertical and horizontal units can be used as indicators for its assessment. Conversely, ...detailed area-wide and updated height information is frequently missing for most urban areas. This study sought to assess three vegetation height classes from a globally available TanDEM-X digital elevation model (DEM, 12 12 m spatial resolution) for Berlin, Germany. Subsequently, height distribution and its accuracy across biotope classes were derived. For this, a TanDEM-X intermediate DEM, a LiDAR DTM, an UltraCamX vegetation layer, and a biotope map were included. The applied framework comprised techniques of data integration and raster algebra for: Deriving a height model for all of Berlin, masking non-vegetated areas, classifying two canopy height models (CHMs) for bushes/shrubs and trees, deriving vegetation heights for 12 biotope classes and assessing accuracies using validation CHMs. The findings highlighted the possibility of assessing vegetation heights for total vegetation, trees and bushes/shrubs with low and consistent offsets of mean heights (total CHM: -1.56 m; CHM for trees: -2.23 m; CHM bushes/shrubs: 0.60 m). Negative offsets are likely caused by X-band canopy penetrations. Between the biotope classes, large variations of height and area were identified (vegetation height/biotope and area/biotope: ~3.50-~16.00 m; 4.44%-96.53%). The framework and results offer a great asset for citywide and spatially explicit assessment of vegetation heights as an input for urban ecology studies, such as investigating habitat diversity based on the vegetation's heterogeneity.
Large-area urban ecology studies often miss information on vertical parameters of vegetation, even though they represent important constituting properties of complex urban ecosystems. The new ...globally available digital elevation model (DEM) of the spaceborne TanDEM-X mission has an unprecedented spatial resolution (12 × 12 m) that allows us to derive such relevant information. So far, suitable approaches using a TanDEM-X DEM for the derivation of a normalized canopy model (nCM) are largely absent. Therefore, this paper aims to obtain digital terrain models (DTMs) for the subsequent computation of two nCMs for urban-like vegetation (e.g., street trees) and forest-like vegetation (e.g., parks), respectively, in Berlin, Germany, using a TanDEM-X DEM and a vegetation mask derived from UltraCam-X data. Initial comparisons between morphological DTM-filter confirm the superior performance of a novel disaggregated progressive morphological filter (DPMF). For improved assessment of a DTM for urban-like vegetation, a modified DPMF and image enhancement methods were applied. For forest-like vegetation, an interpolation and a weighted DPMF approach were compared. Finally, all DTMs were used for nCM calculation. The nCM for urban-like vegetation revealed a mean height of 4.17 m compared to 9.61 m of a validation nCM. For forest-like vegetation, the mean height for the nCM of the weighted filtering approach (9.16 m) produced the best results (validation nCM: 13.55 m). It is concluded that an nCM from TanDEM-X can capture vegetation heights in their appropriate dimension, which can be beneficial for automated height-related vegetation analysis such as comparisons of vegetation carbon storage between several cities.
Urban heat island (UHI) studies have recognized ten factors as increasing the inner-city temperature compared with that of the surrounding suburbs. The UHI effect is a leading cause of heat-related ...diseases and mortality in many nations. However, there are still two main shortcomings. First, the effect of UHI is not well recognized in arid and semi-arid regions. Second, the association of multi-dimensional information with surface temperature in urban areas must be examined. This study focuses on the height-related aspects of urban geometry in an arid region. A range of multispectral and spatial vector data were used to derive the surface temperature and two-dimensional (2D) and three-dimensional (3D) information of the study area. All information was aggregated into a grid with common spatial resolution to create a homogeneous dataset. The machine learning statistical model of a boosted regression tree (BRT) was used to reflect the relative influence of 2D and 3D indicators with land surface temperature. Our results showed a cooler surface temperature in the city than in the surrounding area, leading to the question of whether the established UHI definition encompasses all types of cities. In addition, the thermal band was able to distinguish different spatial structures in the study area. The BRT analysis demonstrated that both multi-dimensional 2D and 3D indicators affect the surface temperature. In particular, the 3D indicators play a more important role than 2D indicators in shaping the surface temperature at different urban geometries of the study area. This new method can help urban planners identify the most influential 2D and 3D indicators that affect the surface temperature in different districts of a city.
Städtische Gehölzflächen haben positive Auswirkungen für Mensch und Natur, wie die Abkühlung überhitzter Innenstädte. Detaillierte Angaben zur Lage, Höhe und Kronenstruktur sind zur Lokalisierung und ...Quantifizierung derartiger Wirkungen unentbehrlich, allerdings auf globalen Maßstab nur für wenige Siedlungsräume verfügbar. In dieser Arbeit werden städtische Baumkronenhöhenmodelle (BHM) aus global verfügbaren digitalen Höhenmodellen (DHM) der TanDEM-X-Mission unter Einbezug zusätzlicher Fernerkundungsdaten und übertragbarer Bildverarbeitungstechniken erstellt sowie deren Anwendbarkeit für stadtökologische Fragestellungen untersucht. Das übergeordnete Ziel der Arbeit ist die Bereitstellung von Ansätzen zur Erstellung und Einbindung großmaßstäblicher, mehrdimensionaler Informationen zu städtischen Gehölzflächen. In einem ersten Schritt wird ein BHM aus einem TanDEM-X DHM unter Verwendung eines zusätzlichen Geländemodells für verschiedene urbane Biotopen der deutschen Stadt Berlin abgeleitet und validiert. Im Anschluss wird in einem neuartigen Ansatz zuerst ein Gelände- und dann ein Kronenmodell für groß- und kleinflächige Gehölzbestände aus einem TanDEM-X-DHM abgeleitet, um die Unabhängigkeit zusätzlicher Höhendaten zu erreichen. Die Genauigkeiten beider Schritte variieren in Abhängigkeit des städtischen Kontextes, wobei Resultate gröber aufgelöster globaler Höhendaten übertroffen werden. Zur Ideenfindung zukünftiger Anwendungen eines BHM in der Stadtforschung wird eine schriftliche Expertenumfrage durchgeführt. Über die Ableitung und Einbindung eines BHM für die iranische Stadt Yazd werden die methodische Übertragbarkeit getestet und Anwendbarkeit demonstriert. Im Gesamtergebnis liefert diese Dissertation validierte Ansätze zur Erstellung und Einbindung großskaliger Flächen- und Höhendaten städtischer Vegetation, die neue Perspektiven für stadtökologische Fragestellungen bieten.
Urban trees and shrubs have a variety of positive effects on humans and nature, such as cooling overheated inner cities. Detailed information on the location, height, and canopy structure of urban woody plants is indispensable for locating and quantifying such effects, but they are only poorly available on large scales. The globally available digital elevation model (DEM) of the TanDEM-X mission seems suitable for deriving the height and structure of woody areas in cities. This work incorporates TanDEM-X’s DEM with additional remote sensing data and transferable image processing techniques to create urban tree canopy height models (CHM) of woody vegetation and investigate their applicability. The overall goal of this thesis is to provide approaches for creating and applying large-scale, multi-dimensional information on urban wooded areas in a holistic framework. In a first step, CHMs are derived from a TanDEM-X DEM and validated using an additional terrain model for different urban biotopes in Berlin, Germany. Next, first a terrain model and then a crown model are derived in a novel approach, to eliminate the need for an additional terrain model. The accuracies of both steps vary depending on the urban context, but exceed results based on global elevation data with coarser resolution. Then, to generate ideas for future applications of a CHM in urban research, a Berlin CHM is presented to a scientific audience in a written survey. By conducting an urban CHM for the Iranian city of Yazd and integrating it into an urban ecological study, the methodological transferability of the model is tested and the applicability is demonstrated. As an overall result, this thesis provides approaches for the processing and specific application of large-scale area and elevation data on urban vegetation, offering a variety of new perspectives on urban ecological issues.
Three-dimensional urban vegetation data provide crucial ecological information, but generally feature poor coverage and availability. The spaceborne radar interferometer TanDEM-X delivers a digital ...elevation model that can be processed to produce urban Canopy Height Models (CHMs), including vegetation height and area per 12-metre cell. To date, these CHMs are underutilised in urban research. This study therefore explores the potential of urban TanDEM-X CHM by combining an expert survey on potential directions for CHM in urban research and a case study conducting and integrating a CHM for climatological research in the city of Yazd, Iran. We complement these empirical analyses with a detailed literature section of the current state of application of TanDEM-X-CHM. The expert survey highlights key research directions and interests for urban CHM implementation. The case study provides an example of implementation based on findings from the expert survey, revealing effects of vegetation height and volume on land surface temperature. Our results underscore the unique characteristics of a TanDEM-X-based CHM, asserting their potential for producing three-dimensional vegetation information crucial for effective research and policy efforts in urban ecology.
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