Uw N‘ .
a >
— CY
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
photosynthesis. PH is generally very low and can thus be
ignored.
2.1.1 Net radiation R,
Surface net radiation R, can be calculated from the incoming
and outgoing radiation fluxes
REK ADD (2)
n
i - us
where À ” (0.15-4 um) is the incoming short-wave radiation, 7
; ; + ;
land surface reflection, L~ (>4 um) the atmospheric long-
s 7 i:
wave radiation, L land surface long-wave radiation.
: ; e Y.
The incoming short-wave radiation flux K' in Eq 2. can be
derived from radiative transfer model MODTRAN by inputting
several location-dependent atmospheric parameters.
Specifically, K can be obtained as
K'z T. K "rop (3)
where the atmospheric short-wave transmittance 7, can be
directly derived from MODTRAN. The spectrally integrated
form of in-band radiation K* TOP is obtained as
Ke (b)cos0
i
K TOP — 3 SUN
d
(4)
|
where K old) is the mean in-band solar exo-atmospheric
o
zog , the
represents the sun zenith angle.
irradiance undisturber by the atmosphere D
earth-sun distance, Om
+
The atmospheric long-wave radiation L can be expressed as
(Win, et al.,1999)
L'azsof'c-ooN-eN-N.) (5)
e 7
£, x].24| —- (6)
a
£, is atmosphere long-wave emissivity, T the atmosphere
temperature on the referral height, N total cloud amount, Nj,
low and middle cloud amounts, c2 and c3 are experiential
factors, e, the actual vapor tension for T, ChPa) .
7
Land surface long-wave radiation L' canbe expressed as
+
L = gol} + (1-¢, )L (7)
&, is land surface emissivity derived from Eq 6, c is Stefan-
Boltzmann constant. T (land surface temperature) can be
derived from the bright temperature of NOAA channels 4 and 5.
2.1.2 The soil heat flux Gy
The regional soil heat flux Gp can be determined by the
following equation (Choudhury and Monteith, 1988)
G, T Ps C, [Uu = T )] / sh (8)
where pO is soil dry bulk density, C soil specific heat, T
land surface temperature , T stand for soil temperature at a
determined height, J, represents soil heat transportation
resistance. Although G can not be directly derived from
satellite remote sensing data, an empirical equation, I" = G, /
R
calculate G from remote sensing data. I, = 0.05 05 is for
4» Was proposed (Menenti et al.,1991; Bastiaanssen, 1995) to
a full vegetation canopy (Monteith 1973) and I: =0315 is
for bare soil (Kustas and Daughtry 1989). An interpolation is
then performed between these two extremes by using the
fractional canopy coverage f. derived from Eq (10). The soil
heat flux G, can thus be parameterized as
G, SR, -[T, «(0-7 7) 47, - T, )] (9)
According to Gutman (1998) , the relationship between t f
and NDVI is found as:
y, NDVI - NDVI,,
c
NDVI NDVI in
NDVI,,,,and NDVI,;, are the maximum and minimum NDV] in
growth seasons. We adopt the NDVI in summer to be the
NDVI, and 0.005 to be NDVI in.
(10)
2.4.3 Sensible Heat flux H
The sensible heat flux (H) is the component that transfers
sensible energy from land surface to atmosphere. The regional
distribution of H can be estimated with a bulk transfer equation
expressed in following form (Monteith,1973)
H = pC, va = T.)
Va
P C, is the atmosphere volume heat capacity, Ta the
(11)
atmosphere temperature in the referral height, T land
surface temperature that can be estimated by the bright
temperature of NOAA channels 4 and 5, 7, is the
aerodynamics resistance.
The aerodynamics resistance }, in Eq 11 is obtained based on
the following edqation:
—d
y, = = Homo )-kB - V, (12)
T Om
and
Zn d
u, = ku[[In( ———-) — VP, ] (13)
0m
where k is the Von-Karman constant , us the friction velocity, z
reference height, d; zero-plane displacement height, Zu the
0m
effective aerodynamic roughness, Y and V the stability
correction functions for momentum and sensible heat transfer
respectively. kB ! is excess resistance to heat transfer
(Chamberlain,1968) and can be derived from the model
proposed by Su et al.(2001).
1315
