eight:
of both
canopy
much
ut the
0% of
/ was
eight,
upper
Shaw
Gotoh
zanopy
40
(96)
d with
yward
Ire are
ments
ighted
| and
anopy
ion of
py is
by the
e area
own in
|f area
1d the
| layer,
6% for
anopy
scause
>anopy
urface
' hand,
atures
for the
Tr is
e and
is, the
leaf temperatures for each layer are different.
Therefore, canopy temperatures, that measured
temperature of leaves facing skyward, depend on
plant canopies that have the different ratios of leaf
area facing skyward.
'93.09.05 '93.09.08
(: 2%
91~120ca
a2)
61—90ca
as E
"g^ E
0~30ca
CD
Sweet corn a Soybean
80 60 40 20 0 20 40 60 80
(96) (96)
Fig. 2 The ratio of leaf area facing skyward to
the area of total vegetation cover.
3.1.3 Number of leaves for each azimuthal direction:
Leaf orientation of eight azimuthal directions for
both plant leaves are shown in Fig. 3. Azimuthal
direction data for corn leaves show an
unhomogeneous distribution, that is, the highest
percentage is inthe northwest and southeast, and
the lowest percentage is in the southwest and
northeast. Also, south directions: southeast, south,
and southwest, have fewer leaves than do the
opposite directions: northeast, north, and
northwest. The percentages of both directions for
total leaves are 33.3% and 45.8%, respectively.
In contrast, the soybean has less directional
preference than does the corn, i.e., the percentages
of number of leaves for south directions
(southeast, south, and southwest) and for north
directions (northeast, north, and northwest) are
39.3% and 39.8%, respectively.
Soybean leaves have a regular leaf orientation
and corn leaves have an irregular leaf orientation
that grows toward spaces within the canopy.
Numbers of leaves for each azimuthal direction of
N "93.09.01
T 25.0 (96)
Sweet corn
TR
Soybean
Fig. 3 Leaf orientation of eight azimuthal
directions for corn and soybeans.
both crops affect the canopy temperature. It can
be assumed that the canopy temperature for the
corn field is lower than that for the soybean field,
because the corn leaves develop to have a higher
vegetation cover ratio than that of the soybeans
leaves.
3.2 Comparisons of leaf temperature
3.2.1 Comparisons of leaf temperature between corn
and soybeans: The results of surface temperature at
the upper-most leaf that was artificially stretched to
a horizontal orientation are shown in Fig. 4. At a
high intensity of solar radiation, leaf temperature for
soybeans is higher than that for corn, and at a low
intensity of solar radiation, leaf temperature for
Soybeans is lower than that of corn. This tendency
is the same for all directions of leaves.
Takechi (1973) has done detailed studies on leaf
temperature. According to his studies, the
difference between leaf temperature and air
temperature depends on leaf absorption of solar
radiation and transpiration. It is assumed that
soybean leaves transpired more than corn leaves in
the case of strong solar radiation.
32 T 1
S.raca Temp.
30 Soybean ] Scuth Leaves
28} N J^ a FA
zal a \ Sweet corn iv
e 24 \i
® 22 X
2 20 ve
S en
D 18 C
|l Surface Temp.
5 30 A vest Leaves
X
= ag) 2 ix
26} oF 7 Sweet corn | \ Soybean
24 " NN NS AT
22 aT X
M ; i
T vi NT
oN -
E 13 :
= o
= 10 33.08.16
=
o 0.8
"S 06 ^
© N
© 04 N
3 X
+ 0.2 i
e 0 ;
08:00 10:00 12:00 14:00 18:00 18:00
Local time(hr.)
Fig. 4 Surface temperature at the upper-most
leaf.
3.22 Comparisons of leaf temperatures for each
azimuthal direction between corn and soybeans: Daily
changes of leaf temperature and the daily mean leaf
temperatures for sunlit and horizontal parts of
leaves at four azimuthal directions within canopies
are shown in Fig. 5 and Fig. 6. Leaf temperature for
soybeans has larger variations at each hour of four
azimuthal directions than that for corn. Also, the
variation of daily mean leaf temperature at four
azimuthal direction for soybeans is large in
comparison with that for corn.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
