1. 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

2. 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

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

4. 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

5. 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

6. 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 (%)

7. 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)

8. 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 (%)

9. 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 km

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

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

12. 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

13. 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

14. Thank you for your attention.