Surface Heat Balance Analysis by using ASTER and Formosat-2 data Soushi Kato Department of Earth Sciences, Earth Dynamic System Research Center, National Cheng Kung University 2008. 3. 11

Introduction Estimation of surface heat balance in urban area helpful to understand the causes of heat island effect Using Remote Sensing data useful to obtain spatial pattern RS data with high spatial resolution and wide spectral coverage are suitable to heat balance estimation

ASTER and Formosat-2 ASTER VNIR Formosat-2 Visible & NIR 3 band 15m resolution SWIR TIR 6 band 5 band 30 m 90 m Visible & NIR 4 band 8 m & 2 m resolution False-color images around NCKU, Taiwan (NIR, Green, Red)

Sensible heat flux increase → Heat island phenomenon Surface Heat Balance Net radiation Short- and longwave radiation Sensible heat Surface-atmosphere temperature difference Latent heat Evapotranspiration H LE Rn G A Surface Ground heat Surface-subsurface temperature difference Anthropogenic heat Energy consumption Rn + A = H + LE + G Sensible heat flux increase → Heat island phenomenon

Storage Heat Flux (DG) DG = G – A = Rn – H – LE Ground heat (G) Anthropogenic heat (A) Difficult to obtain through a wide area Net radiation Sensible heat Latent heat DG = G – A = Rn – H – LE Rn H LE [W/m2] G A Combine G and A Estimated by Rn, H and LE Ground heat Anthropogenic heat Based on the method for ground measurement (e.g. Oke et al., 1999) Rn H LE DG > 0 ⇒ Heat storage Storage heat flux DG DG < 0 ⇒ Heat discharge

Net Radiation (Rn) Estimation Rn = (1 ｰ a) Rs + es RL↓ｰ RL↑ 　　 　 RL↓ RL↑ a : Albedo Rs Reflectance (Liang, 2000) Rs : Solar radiation (W/m2) a es RL : Longwave radiation (W/m2) = ei s Ti4 (Stefan-Boltzmann’s law) Ta : Atmospheric temperature (K)　　 Ts : Surface temperature (K) es : Surface emissivity (absorptance) (Ogawa et al., 2003) ea : Atmospheric emissivity (Prata, 1996) Atmospheric temperature (K) Relative humidity (%)

Sensible Heat Flux (H) Estimation Ts – Ta ra H = rCp Ta 　　　 Bulk resistance approach ra 　　　 Ts　　　　　　 r : Air density (kg/m3) Cp : Specific heat of air at constant pressure (J/kg K) Ts : Surface temperature (K) Ta : Atmospheric temperature (K) ra : Aerodynamic resistance (s/m) Wind speed (m/s) Roughness length (m) 　 Surface type (Brutsaert, 1982; Kondo, 1994; Yasuda, 1995)

Latent Heat Flux (LE) Estimation rCp g es* – ea ra + rs ra rs Bulk resistance approach es* r : Air density (kg/m3) Cp : Specific heat of air at constant pressure (J/kg K) es* : Saturation vapor pressure (hPa) ea : Vapor pressure (hPa) g : Psychrometric constant (hPa/k) ra : Aerodynamic resisntance (s/m) rs : Stomatal resistance (s/m) 　(Nishida et al., 2003) Surface temperature (K) Air temperature (K) Solar radiation (W/m2) Minimum rs (s/m) 　　Surface type Air temperature (K) Relative humidity (%)

Data Used false color (NIR: Green: Red) Study area Tainan, Taiwan Satellite data ASTER 2000 / 3 / 6 Formosat-2 2004 / 7 / 12 Meteorological data Meteorological Station Tainan 2000 / 3 / 6 0 5km

Surface Classification Map Derived from Maximum likelihood method and manual correction Formosat-2 Urban Road Water Bare soil Short grass Tall grass Bush Forest

Comparison of Classification Maps Surface classification map around Tainan Station ASTER Formosat-2 0 1km Roads and vegetations are distinguished more clearly

Heat Fluxes by ASTER & Formosat-2 Net radiation Rn Sensible heat H Latent heat LE 190 　　　 360 W/m2 -5 　　　 120 W/m2 0 　　　 90 W/m2 Storage heat DG 40 　　　 360 W/m2

Further Study Usage of ASTER and Formosat-2 data acquired on the same (at least closer) dates 2-m resolution pan-sharpened Formosat-2 image ASTER 15m Formosat-2 8m Formosat-2 2m

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