Addendum
CIRAS-2 Operator's Manual Version 2.04
- 163 -
For clarity in the following expansion let (el - ea) = D (vapor pressure deficit).
Then from (1) and (2):
N
E
RB
D
N
E
RSu
*
*
*
2
*
1
and :
N
E
RB
E
RB
D
N
E
RSu
*
*
*
2
*
*
2
*
1
Therefore :
N
E
RB
E
RB
D
N
E
RB
D
N
E
RB
D
N
E
E
N
E
RB
E
RB
D
N
E
RSl
RSu
*
*
*
2
*
*
2
*
*
*
*
2
*
*
*
2
*
*
*
*
*
2
*
*
2
*
*
1
1
Now,
RSl
1
RSu
1
1
RS
Therefore:
N
E
RB
D
N
E
E
N
E
RB
E
RB
D
N
E
N
E
RB
E
RB
D
N
E
RB
D
RS
*
*
*
2
*
*
*
*
*
2
*
*
2
*
*
*
*
*
2
*
*
2
*
*
*
*
2
Which expands to:
N
N
E
RB
N
E
RB
D
E
N
N
E
E
RB
RB
N
E
E
RB
RB
D
E
RB
D
D
RS
*
*
*
*
4
*
*
*
4
*
*
*
*
*
*
*
4
*
*
*
*
*
4
*
*
*
2
*
(3)
If we assume that there is equal transpiration on both surfaces (i.e. N = 0.5), then:
E
E
RB
D
eq
RS
*
)
(
(4)
The error in determination of RS from making the assumption of equal transpiration on both sides of the
leaf is (3) - (4).
After expansion and simplification this becomes:
D
N
N
E
RB
N
N
1
*
*
25
.
0
25
.
0
1
*
(5)
