5 research outputs found
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Urban morphology parameters from global digital elevation models: implications for aerodynamic roughness for wind-speed estimation
Urban morphology and aerodynamic roughness parameters are derived from three global digital elevation models (GDEM): Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Shuttle Radar Topography Mission (SRTM), and TanDEM-X. Initially, each is compared to benchmark elevation data in London (UK). A moving window extracts ground heights from the GDEMs, generating terrain models with root-mean-square accuracy of up to 3 m. Subtraction of extracted ground heights provides roughness-element heights only, allowing for calculation of morphology parameters. The parameters are calculated for eight directional sectors of 1 km grid-squares. Apparent merging of roughness elements in all GDEMs causes height-based parameter underestimation, whilst plan and frontal areas are over- and under-estimated, respectively. Combined, these lead to an underestimation of morphometrically-derived aerodynamic roughness parameters. Parameter errors are least for the TanDEM-X data. Further comparison in five cities (Auckland, Greater London, New York, Sao Paulo, Tokyo) provides basis for empirical corrections to TanDEM-X-derived geometric parameters. These reduce the error in parameters across the cities and for a separate location. Meteorological observations in central London give insight to wind-speed estimation accuracy using roughness parameters from the different elevation databases. The proposed corrections to TanDEM-X parameters lead to improved wind-speed estimates, which combined with the improved spatial representation of parameters across cities demonstrates their potential for use in future studies
Large-scale 3D Modelling of the Built Environment - Joint Analysis of TanDEM-X, Sentinel-2 and Open Street Map Data
Continental to global scale mapping of the human settlement extent based on earth observation satellite data has made considerable progress. Nevertheless, the current approaches only provide a two-dimensional representation of the built environment. Therewith, a full characterization
is restricted in terms of the urban morphology and built-up density, which can only be gained by a detailed examination of the vertical settlement extent. This paper introduces a methodology for the extraction of three-dimensional (3D) information on human settlements by analyzing the digital elevation and radar intensity data collected by the German TanDEM-X satellite mission in
combination with multispectral Sentinel-2 imagery and data from the Open Street Map initiative and the Global Urban Footprint human settlement mask. The first module of the underlying processor generates a normalized digital surface model from the TanDEM-X digital elevation model for all regions marked as a built-up area by the Global Urban Footprint. The second module generates a building mask based on a joint processing of Open Street Map, TanDEM-X/TerraSAR-X radar images, the calculated normalized digital surface model and Sentinel-2 imagery. Finally, a third module allocates the local relative heights of the normalized digital surface model to the building structures provided by the building mask. The outcome of the procedure is a 3D map of the built environment showing the estimated local height for all identified vertical building structures at 12 m spatial resolution. The results of a first validation campaign based on reference data collected for the seven cities of Amsterdam (NL), Indianapolis (US), Kigali (RW), Munich (DE), New York (US), Vienna (AT), and Washington (US) indicate the potential of the proposed methodology to accurately estimate the distribution of building heights within the built-up area
Interferometric Synthetic Aperture RADAR and Radargrammetry towards the Categorization of Building Changes
The purpose of this work is the investigation of SAR techniques relying on multi image acquisition for fully automatic and rapid change detection analysis at building level. In particular, the benefits and limitations of a complementary use of two specific SAR techniques, InSAR and radargrammetry, in an emergency context are examined in term of quickness, globality and accuracy. The analysis is performed using spaceborne SAR data
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Surface roughness parameters in cities: improvements and implications for windspeed estimation
The surface aerodynamic roughness parameters of the zero-plane displacement (zd) and
roughness length (z0) can be critical for wind-speed estimates in the atmospheric boundary layer.
In urban areas, the numerous sources and sinks of momentum makes it challenging to assign
appropriate values for zd and z0. The objective of this PhD is to improve the understanding of zd
and z0 in urban environments, especially for wind-speed estimates when flow is free from
roughness-element wakes.
Nine methods are applied to determine zd and z0 at three sites in central London (UK),
demonstrating the inter-method variability leads to a wide range of values. Wind-speed
estimates using the roughness parameters and five wind-speed profile methods are compared
to Doppler lidar observations up to 200 m (approximately 10 times the average building height)
above the canopy. Estimates with roughness parameters determined from morphometric
methods (i.e. based upon surface geometry) which directly incorporate roughness-element
height variability are consistently most accurate.
A morphometric method is developed to calculate zd and z0 that accounts for both buildings and
vegetation. The method captures the directional and seasonal variability of roughness with
vegetation and improves the accuracy of wind-speed estimates.
Due to the challenge of obtaining urban morphology and roughness parameters for cities
globally, three satellite-derived global digital elevation models (GDEMs) are assessed using
benchmark elevation datasets. It is concluded that empirical corrections to the most accurate
GDEM (TanDEM-X) can improve the parameter accuracy and associated wind-speed estimates