LI-COR LI-6400, Руководство пользователя

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Using an Energy Balance
Energy Balance And Boundary Layer
Using the LI-6400 17-9
Air Temperature
The third parameter is the air temperature next to the leaf. The LI-6400 has
sensors for this only in the 6400-05, -07, and -08 chambers, so in the rest of
the chambers we use the leaf thermocouple to do this job (variable
tLeaf_C ),
by pulling it down a bit so that the junction is not in contact with any leaf ma-
terial. Also, try to keep the junction shaded if possible to minimize radiation
errors.
Boundary Layer Conductance
The fourth parameter is the one-sided boundary layer conductance, which is
available as global variable
condBL_one .
Transpiration Rate
The final parameter is transpiration rate, which is user variable number 20.
If these assumptions are inadequate for your application, then you should
modify the ComputeList accordingly (and rename it to keep it separate)
.
Recomputation Considerations
The recomputation option available in OPENÕs Utility Menu allows you to
change any of the following: user equations, output formats, absorbed radia-
tion coefficients, area, boundary layer conductance, and stomatal ratio. Note,
however, that if you use the leaf temperature thermocouple to measure air
temperature (as we recommend), then you canÕt go back and recompute
with-
out using the energy balance, because you will not have a measured leaf tem-
perature.
Each of OPENÕs log files contains header information telling what user equa-
tions, light source, output format, etc. were used for that file. Thus, you can
easily tell after the fact what mode you were in when looking at old data.
Energy Balance And Boundary Layer
Measuring the boundary layer conductance for broadleaves in LI-6400 cham-
bers can be done using saturated filter paper to simulate a leaf. The problem
with this experiment, however, is that the leaf can be 10C cooler than the air,
and the leaf temperature thermocouple will always underestimate that differ-
ence, because of conduction errors along the wires.
We can bring an energy balance analysis to bear on this problem, with the ob-
jective of finding an equation that will compute both leaf temperature, and
boundary layer conductance. This requires the following simplifications: