LI-COR LI-830 - Calibration and Broadening Equations

Appendix A. Equation Summary
H
2
O Equations (LI-850 only)
Absorptance α
ω
for water vapor is computed from
A-6
where V
w
and V
wo
are the sample and reference raw detector readings, and Z
w
is
the zero parameter. The pressure correction for water vapor is an empirical func-
tion g
w
() of absorptance and pressure P:
A-7
The value of P
o
is 99 kPa. When the pressure correction is not enabled, g
w
() is
simply 1.0. Water vapor concentration W (mmol mol
-1
) is computed from
A-8
where f
w
(x) is a third order polynomial whose coefficients are given on the cal-
ibration sheet.
A-9
CO
2
Equations
The measurement of CO
2
is a bit more complicated than for H
2
O because of the
influence of water vapor. There is a slight direct cross sensitivity in the CO
2
signal
to H
2
O. This is measured at the factory and accounted for in the computation of
absorptance (equation A-10). There is also a band broadening effect that is accoun-
ted for in the computation of concentration (equation A-14).
CO
2
absorptance α c is computed from
A-10
A-2 Using the LI-830 and LI-850 Gas Analyzers