Figure 3 shows the study area from the LANDSAT
TM(Path/Row: 116/34) which obtained on 15 Apr. 1986
and 22 Sept. 1992, respectively. From this figure. the
large land cover change due to the land reclamation is
visible to naked eye.
3. PARAMETERIZATION OF SURFACE ENERGY
BALANCE COMPONENTS
3-1. Net Radiation, Rn
The net radiation at the land surface is the sum of
incoming and outgoing spectral radiant fluxes integrated
over all wavelengths and given by
Rn=(1-a)- -S¢ +L -LT -————————————————2)
where Rn is the net radiation(W/m' ), a. is the surface
albedo, Sl is incoming solar irradiance, L4 is incoming
longwave radiation from atmosphere, LT is the
outgoing longwave radiation from the land surface.
Each components of equation 2) were computed as
follows:
Shortwave radiation(W/m?): For each grid,
incoming shortwave radiation(0.15~ 4m) was
estimated from the cloudiness, digital elevation model,
and solar geometry. In this procedure, the topographic
effects were considered: direct irradiance(Rsdir), diffuse
irradiamce(Rsdif) and reflected irradiance(Rsref). The
total irradiance on a tilted surface can be estimated by
integrating those three components as follows:
Rsi =(a+b-n/N)-(Rsdir+ Rsdif + Rsref) —-3)
Rsdir - Isc- Eo: Pt" sin h' 4)
Rsdif = OSes pnd Pl ltem —-5)
1-14In Pt 2
Rsref » a |Isc - Eo: Pt" -sinh' C6)
1- Pi" , 1-cosB
05 - Isc - Eo - sinh
THYTTU 2
where Isc is the solar constant, Eo is the eccentricity
correction factor of earth, A is the solar altitude, A’ is
the altitude of the sun for a sloping surface, Pt is the
atmospheric transmission coefficient, g is the slope
angle of the surface, m is the relative optical air mass,
nN is the cloudiness(the relative duration of sunshine).
Albedo: Albedo was calculated using spectral
reflectance factors for representative bands in the visible
and near infrared bands of LANDSAT TM(Brest and
Goward, 1987). For vegetated surfaces Brest and
Goward calculated a as
a = 0.526P(TM2) + 0.362P(TM4) + 0.112P(TM7) --7)
32
for non-vegetated surfaces
x, 7 0,526p(TM2) * 0.474 D(TMA) M8 8)
where P(TM) is the reflectance of each TM band.
Longwave radiation(W/m^): Incoming and
outgoing longwave radiation( > 4um)also was
calculated using air temperature, surface temperature
which extracted from TM band 6, and vapor pressure
data in the following formula(Satterlund, 1979)
incomming longwave radiation:
LL = LO8 [1 — exp(-e, T, / 2016)] 0-Tg* ---9)
outgoing longwave radiation:
Lt uot 7
10)
where e, is the emissivity of the surface, c is the Stefan-
Boltzman constant(7 5.67108 W m? K-4), and 7; is
the surface temperature(°K ). T, is the air temperature(
° K)and e, is water vapor pressure(mb), respectively.
3-2. Sensible Heat Flux, H
The one-dimensional bulk resistance equation
computes the sensible heat flux(H) with the
surface(T,)-air temperature difference( T,) and
windspeed(4), i.e.,
H m p Cp(Ts T Ta) 11)
Ia
where D. is the density of air(kg m^), Cp is the specific
heat of air at constant pressure(=1004.7 J kg! K'!), 75
is the aerodynamic resistance(sm’!). 7, can be computed
using surface roughness( z,; m), displacement height
(d ; m) as follows:
si-de 2,)/ z, Y,
ku
12)
a
where K is the von-Karaman's constant(= 0.4), Z is the
measurement height(m). The surface roughness and
displacement height were can be estimated using canopy
height(Brutsaert, 1982).
3-3. Soil Heat Flux, G
The empirical data has shown that there is a reasonable
relationship between the ratio G / RA? and. normalized
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
