LI-COR LI-6400, Руководство пользователя

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Using an Energy Balance
Using Energy Balance in OPEN
17-8 Using the LI-6400
17
Each of these compute lists add two new user variables, EBdT and EBTlf . The
first uses the LPL function EB_DeltaT() to compute the leaf-air temperature
difference. This function implements Equation (17-8), takes five parameters,
and returns the leaf-air temperature difference (Table 15-3 on page 15-15).
EB_DeltaT( parIn_um * alphaK, tCham_c, tLeaf_C,
condBL_one, #20)
Absorbed Energy
The first parameter is the energy absorbed by the leaf. The global variable al-
phaK is the product of the two multipliers ( and k ) in (17-2). This product
is given in Table 17-1 on page 17-4, and is set via the Lightsource= configu-
ration command (page 16-21). The variable
parIn_um is the current reading
of the in-chamber light sensor.
If the chamber has a clear bottom, then the incident PAR would be larger than
measured by the uplooking chamber light sensor. For this reason, in the Com-
puteList file Ò
Clear Bottom EB
Ó, the call to EB_DeltaT looks a bit different:
EB_DeltaT( parIn_um * alphaK * 1.2,tCham_c,tLeaf_C,condBL_one,#20)
The parIn_um value is increased 20% to account for the clear bottom.
The third variation on the theme is provided by Ò
Conifer Chamber EB
Ó, which has
no in-chamber PAR sensor, so the external one must be used. Accordingly,
the call to
EB_DeltaT looks like this:
EB_DeltaT( parOut_um * alphaK, tCham_c, tLeaf_C, condBL_one, #20)
Wall Temperature
The second parameter needed for the EB_DeltaT function is wall tempera-
ture. The LI-6400 doesnÕt have such a sensor per se, but the air temperature
thermistor is located in the IRGA beneath the air circulation fan. Between this
location and the leaf chamber, the air comes in contact with a lot of metal wall
material, so this sensorÕs signal is not a bad first guess for wall temperature.
However, the metal and Propafilm pieces of the leaf chamber itself will be
modified by external air, but we have no way of measuring that with the de-
fault instrument. Thus, we use
tCham_C for wall temperature. If the coolers
are on, then the farther the set point is from ambient temperature, the worse
this assumption becomes.
Fortunately, however, wall temperature is not that
critical in the analysis.
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