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Urban-rural air temperature patterns from remotely sensed land surface temperature Koen De Ridder, Bino Maiheu, VITO – Flemish Institute for Technological Research, Mol, Belgium Enrique Montero, INDRA Espacio, Madrid, Spain Giulio Ceriola, Paolo Manunta, Monique Viel, Planetek Italia, Bari, Italy Iphigenia Keramitsoglou, Vassilis Amiridis, NOA – National Observatory of Athens, Athens, Greece Marc Paganini, ESA-ESRIN, Frascati, Italy Bénédicte Dousset, University of Hawaï, Honolulu, Hawaï, USA José Sobrino, University of Valencia, Valencia, Spain Kostas Kourtidis, Democritus University of Thrace, Xanthi, Greece Xavier Briotet, ONERA, Toulouse, France

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urban heat island phenomenon – impacts

health

“The evidence that heat waves can result in both increased deaths and illness is substantial, and concern over this issue is rising because of climate change”

energy consumption

Reid CE, O’Neill MS, Gronlund CJ, Brines SJ, Brown DG, Diez-Roux AV, et al. 2009. Mapping Community Determinants of Heat Vulnerability. Environ Health Perspect 117:1730-1736.

Sailor, D. J. 2002. Urban Heat Islands, Opportunities and Challenges for Mitigation and Adaptation. Sample Electric Load Data for New Orleans, LA (NOPSI, 1995). North American Urban Heat Island Summit. Toronto, Canada. 1–4 May 2002. Data courtesy Entergy Corporation.

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ESA-UHI project – objectives

» demonstrate use of thermal infrared (TIR) satellite imagery to map urban heat island characteristics for ten European cities and using different sensors (SEVIRI, AVHRR, ASTER, …)

» thermal remote sensing alone is not sufficient to describe the urban heat island need to determine air temperature from land surface temperature imagery

» this presentation focuses on » retrieval of air temperature from ASTER TIR imagery» case study for the Madrid area

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ASTER – Advanced Spaceborne Thermal Emission and Reflection Radiometer

» onboard Terra platform» channels:

» visible / near infrared» short-wave infared» thermal infrared

» five thermal channels» range 8.125 – 11.65 µm» spatial resolution 90 m

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land surface temperature derived from ASTER

Madrid area, 25 June 2008, 22:18 UT

atmospheric and surface emissivity corrections

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method (1)

1. calculate turbulent sensible heat flux H from

a. vertical temperature gradient Ts-Ta

b. aerodynamic resistance rah

2. use H as lower boundary condition in a numerical advection-diffusion model, forced by ECMWF large-scale forcing

3. update air temperature Ta using this model

4. back to step 1.

background air temperature

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method (2)

» ASTER pixels are characterized by a single temperature only while they are composed of a mixture of land cover types (vegetation, soil, urban, …)

» this requires the specification of aggregated values for» momentum roughness length z0 ( Mason, 1988)

» thermal roughness length z0t ( Beljaars and Holtslag, 1991)

» specification of kB-1 [ ln(z0/z0t)]

» kB-1 = 2 over vegetation» over cities Zilitinkevich (1970)

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validation

ASTER 25 June 2008 22:18 UTASTER 25 June 2008 11:13 UT

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day versus night air temperature

% sealed soil surfaces 2-m air temperature 25 June 2008 11:13 UT

2-m air temperature 25 June 2008 22:18 UT

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air temperature transects across Retiro Park

day

night

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conclusions

» we implemented » an aerodynamic method to obtain sensible heat flux from satellite

surface temperature, » coupled to a coarse atmospheric model to estimate background air

temperature

» validation for Madrid for a day/night image pair yielded » average errors of the order of 1°C » pattern correlation coefficients 0.8

» it was found that» the UHI is stronger at night than during the day» cooling effect Retiro park 0.5-1.5 °C (background temperature!)