| 1. |
- Kent, Christoph W., et al.
(författare)
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Evaluation of Urban Local-Scale Aerodynamic Parameters: Implications for the Vertical Profile of Wind Speed and for Source Areas
- 2017
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Ingår i: Boundary-Layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 164:2, s. 183-213
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 The Author(s)Nine methods to determine local-scale aerodynamic roughness length (Formula presented.) and zero-plane displacement (Formula presented.) are compared at three sites (within 60 m of each other) in London, UK. Methods include three anemometric (single-level high frequency observations), six morphometric (surface geometry) and one reference-based approach (look-up tables). A footprint model is used with the morphometric methods in an iterative procedure. The results are insensitive to the initial (Formula presented.) and (Formula presented.) estimates. Across the three sites, (Formula presented.) varies between 5 and 45 m depending upon the method used. Morphometric methods that incorporate roughness-element height variability agree better with anemometric methods, indicating (Formula presented.) is consistently greater than the local mean building height. Depending upon method and wind direction, (Formula presented.) varies between 0.1 and 5 m with morphometric (Formula presented.) consistently being 2–3 m larger than the anemometric (Formula presented.). No morphometric method consistently resembles the anemometric methods. Wind-speed profiles observed with Doppler lidar provide additional data with which to assess the methods. Locally determined roughness parameters are used to extrapolate wind-speed profiles to a height roughly 200 m above the canopy. Wind-speed profiles extrapolated based on morphometric methods that account for roughness-element height variability are most similar to observations. The extent of the modelled source area for measurements varies by up to a factor of three, depending upon the morphometric method used to determine (Formula presented.) and (Formula presented.).
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| 2. |
- Landier, Lucas, et al.
(författare)
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3D modeling of radiative transfer and energy balance in urban canopies combined to remote sensing acquisitions
- 2016
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Ingår i: IGARSS 2016 - 2016 IEEE International Geoscience and Remote Sensing Symposium. - 2153-7003.
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Konferensbidrag (refereegranskat)abstract
- In this paper we present a study on the use of remote sensing data combined to the 3D modeling of radiative transfer (RT) and energy balance in urban canopies in the aim to improve our knowledge on anthropogenic heat fluxes in several European cities (London, Basel, Heraklion, and Toulouse). The approach is based on the forcing by the use of LandSAT8 data of a coupled radiative transfer model DART (Direct Anisotropic Radiative Transfer) (www.cesbio.upstlse.fr/dart) with an energy balance module. LandSAT8 visible remote sensing data is used to better parametrize the albedo of the urban canopy and thermal remote sensing data is used to enhance the anthropogenic component in the coupled model. This work is conducted in the frame of the H2020 project URBANFLUXES, which aim is to improve the efficiency of remote-sensing data usage for the determination of the anthropogenic heat fluxes in urban canopies
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| 3. |
- Landier, Lucas, et al.
(författare)
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Calibration of DART Radiative Transfer Model with Satellite Images for Simulating Albedo and Thermal Irradiance Images and 3D Radiative Budget of Urban Environment
- 2016
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Ingår i: 36th EARSeL Symposium, 20-24 June 2016, Bonn, Germany.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Remote sensing is increasingly used for managing urban environment. In this context, the H2020 project URBANFLUXES aims to improve our knowledge on urban anthropogenic heat fluxes, with the specific study of three cities: London, Basel and Heraklion. Usually, one expects to derive directly 2 major urban parameters from remote sensing: the albedo and thermal irradiance. However, the determination of these two parameters is seriously hampered by complexity of urban architecture. For example, urban reflectance and brightness temperature are far from isotropic and are spatially heterogeneous. Hence, radiative transfer models that consider the complexity of urban architecture when simulating remote sensing signals are essential tools. Even for these sophisticated models, there is a major constraint for an operational use of remote sensing: the complex 3D distribution of optical properties and temperatures in urban environments. Here, the work is conducted with the DART (Discrete Anisotropic Radiative Transfer) model. It is a comprehensive physically based 3D radiative transfer model that simulates optical signals at the entrance of imaging spectro-radiometers and LiDAR scanners on board of satellites and airplanes, as well as the 3D radiative budget, of urban and natural landscapes for any experimental (atmosphere, topography,…) and instrumental (sensor altitude, spatial resolution, UV to thermal infrared,…) configuration. Paul Sabatier University distributes free licenses for research activities. This paper presents the calibration of DART model with high spatial resolution satellite images (Landsat 8, Sentinel 2, etc.) that are acquired in the visible (VIS) / near infrared (NIR) domain and in the thermal infrared (TIR) domain. Here, the work is conducted with an atmospherically corrected Landsat 8 image and Bale city, with its urban database. The calibration approach in the VIS/IR domain encompasses 5 steps for computing the 2D distribution (image) of urban albedo at satellite spatial resolution. (1) DART simulation of satellite image at very high spatial resolution (e.g., 50cm) per satellite spectral band. Atmosphere conditions are specific to the satellite image acquisition. (2) Spatial resampling of DART image at the coarser spatial resolution of the available satellite image, per spectral band. (3) Iterative derivation of the urban surfaces (roofs, walls, streets, vegetation,…) optical properties as derived from pixel-wise comparison of DART and satellite images, independently per spectral band. (4) Computation of the band albedo image of the city, per spectral band. (5) Computation of the image of the city albedo and VIS/NIR exitance, as an integral over all satellite spectral bands. In order to get a time series of albedo and VIS/NIR exitance, even in the absence of satellite images, ECMWF information about local irradiance and atmosphere conditions are used. A similar approach is used for calculating the city thermal exitance using satellite images acquired in the thermal infrared domain. Finally, DART simulations that are conducted with the optical properties derived from remote sensing images give also the 3D radiative budget of the city at any date including the date of the satellite image acquisition.
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| 4. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Impact of city changes and weather on anthropogenic heat flux in Europe 1995–2015
- 2013
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Ingår i: Urban Climate. - 2212-0955. ; 4, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- How people live, work, move from place to place, consume and the technologies they use all affect heat emissions in a city which influences urban weather and climate. Here we document changes to a global anthropogenic heat flux (QF) model to enhance its spatial (30'' x 30'' to 0.5° x 0.5°) resolution and temporal coverage (historical, current and future). QF is estimated across Europe (1995–2015), considering changes in temperature, population and energy use. While on average QF is small (of the order 1.9–4.6Wm2 across all the urban areas of Europe), significant spatial variability is documented (maximum 185Wm2). Changes in energy consumption due to changes in climate are predicted to cause a 13% (11%) increase in QF on summer (winter) weekdays. The largest impact results from changes in temperature conditions which influences building energy use; for winter, with the coldest February on record, the mean flux for urban areas of Europe is 4.56 W m-2 and for summer (warmest July on record) is 2.23 W m-2. Detailed results from London highlight the spatial resolution used to model the QF is critical and must be appropriate for the application at hand, whether scientific understanding or decision making.
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| 5. |
- Loridan, Thomas, et al.
(författare)
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High Resolution Simulation of the Variability of Surface Energy Balance Fluxes Across Central London with Urban Zones for Energy Partitioning
- 2013
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Ingår i: Boundary-Layer Meteorology. - : Springer Netherlands. - 0006-8314 .- 1573-1472. ; 147:3, s. 493-523
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Tidskriftsartikel (refereegranskat)abstract
- The parameterization of surface heat-flux variability in urban areas relies on adequate representation of surface characteristics. Given the horizontal resolutions (e.g. ≈ 0.1–1 km) currently used in numerical weather prediction (NWP) models, properties of the urban surface (e.g. vegetated/built surfaces, street-canyon geometries) often have large spatial variability. Here, a new approach based on Urban Zones to characterize Energy partitioning (UZE) is tested within a NWP model (Weather Research and Forecasting model; WRF v3.2.1) for Greater London. The urban land-surface scheme is the Noah/Single-Layer Urban Canopy Model (SLUCM). Detailed surface information (horizontal resolution 1 km) in central London shows that the UZE offers better characterization of surface properties and their variability compared to default WRF-SLUCM input parameters. In situ observations of the surface energy fluxes and near-surface meteorological variables are used to select the radiation and turbulence parameterization schemes and to evaluate the land-surface scheme and choice of surface parameters. For radiative fluxes, improved performance (e.g. > 25 W m −2 root-mean-square error reduction for the net radiation) is attained with UZE parameters compared to the WRF v3.2.1 default for all three methods from the simplest to the most detailed. The UZE-based spatial fluxes reproduce a priori expectations of greater energy storage and less evaporation in the dense city centre compared to the residential surroundings. Problems in Noah/SLUCM partitioning of energy between the daytime turbulent fluxes are identified with the overestimation of the turbulent sensible heat and underestimation of the turbulent latent heat fluxes.
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| 6. |
- Magliulo, Vicenzo, et al.
(författare)
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Environmental measurements in BRIDGE case studies
- 2015
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Ingår i: Understanding Urban Metabolism: A Tool for Urban Planning. - : Routledge. - 9780415835114 ; , s. 45-57
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Ward, Helen, et al.
(författare)
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Using observations to improve modelled energy, water and carbon exchanges for urban areas
- 2015
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Ingår i: ICUC9 – 9 th International Conference on Urban Climate jointly with 12th Symposium on the Urban Environment. 20-24 July 2015, Toulouse, France.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Models are an essential tool for studying how our surroundings influence us and how we, intentionally or inadvertently, influence our surroundings. The Surface Urban Energy and Water balance Scheme (SUEWS) uses a basic meteorological forcing dataset and information about the surface cover to model components of the energy and water balance. The model was initially developed based on studies in North America and is now being run for multiple locations around the world. Here, we evaluate the model at two locations in the UK. A network of micrometeorological observations exists across London, enabling comparisons between the city centre and suburbs. The central London study site is one of the most highly urbanised and densely populated to date. 120 km to the west is the typical suburban town of Swindon. At both of these locations, extensive observational datasets spanning several years have been collected, and work has been undertaken to classify the surface characteristics. However, as detailed land cover and socio-economic information may not always be available, we consider the impact on model performance of using only easily accessible data to provide the required inputs. SUEWS is evaluated against observations of energy and water balance components (including turbulent heat fluxes from eddy covariance and scintillometry techniques). SUEWS estimates evaporation using an adapted Penman-Monteith formulation with a variable surface conductance. Analysis of observed surface conductances suggests adjustments to improve model performance. CO2 fluxes, closely linked to the surface conductance, are also examined. The central London and suburban Swindon sites behave differently, in terms of both the magnitude and temporal variability of CO2 exchanges. These differences are almost entirely a result of land use and land cover, and associated patterns of human behaviour. Simple models based on anthropogenic emissions inventories provide an indication of the magnitude of the CO2 release, however, at the suburban site vegetation plays an important role in CO2 uptake and must be incorporated too. With improved modelling capability, the exposure of the population to risks such as thermal stress or flooding can be better estimated. Having validated the model, the impact of policy decisions and future climate scenarios on the wellbeing of the citizens can be assessed.
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