LI-COR LI-8100A - Page 391

D Equation Summary:
Final Variables
As described in Section 3, About LI-8100A Data Records, the Summary Records
consist of a number of Measured Variables, some of which appear in all
Observations, and some of which are optional, and a number of Final Variables of
Type 2, 3, or 4, as shown in Table 3-1.
As described in Section 4, Theory of Operation, the value of C
dry
is the
instantaneous water-corrected chamber CO
2
mole fraction called C'(t)in equation
(4-13); its initial value is computed from the intercept of a linear regression of the
first 10 points after the chamber closes. This is used as a parameter in the non-
linear regression that fits equation (4-13) to the C'(t) vs t data between the end of
the Dead Band and the end of the observation. This regression yields values
needed to obtain the soil CO
2
efflux rate. The discussion below describes how the
appropriate slope of C
dry
is computed and used to compute the Final Variables in
the LI-8100A Summary Records.
Computing the slope of C
dry
requires a three-step process:
1. Fit C
dry
vs E
time
for Type 1 data. This is called function f(t), which is shown in
Equation (4-13).
2. Compute time t
0
such that
t
0
= f
-1
(C
0
) D-1
where C
0
is the initial value of C
dry
.
3. Compute the slope from the derivative of f(t) at time t
0
:
∂
∂
∂
∂
C
t
dry
t
ft= ()
0
D-2
Standard error of this slope (used for the Type 4 value of "Cdry/t") is given by