5 in-situ calibration theory, In-situ calibration theory – Campbell Scientific HFP01SC Hukseflux Self-Calibrating Soil Heat Flux Plate User Manual
Page 29
Model HFP01SC Self-Calibrating Soil Heat Flux Plate
θ
ρ
ρ
θ
m
w
b
v
=
(2)
where C
S
is the heat capacity of moist soil, ρ
b
is the bulk density, ρ
w
is the
density of water, C
d
is the heat capacity of a dry mineral soil, θ
m
is the soil
water content on a mass basis, θ
v
is the soil water content on a volume basis,
and C
w
is the heat capacity of water.
This calculation requires site specific inputs for bulk density, mass basis soil
water content or volume basis soil water content, and the specific heat of the
dry soil. Bulk density and mass basis soil water content can be found by
sampling (Klute, 1986). The volumetric soil water content is measured by the
CS616 water content reflectometer. A value of 840 J kg
-1
K
-1
for the heat
capacity of dry soil is a reasonable value for most mineral soils (Hanks and
Ashcroft, 1980).
The storage term is then given by Equation 3 and the soil heat flux at the surface is
given by Equation 4.
S
T C d
t
s s
=
∆
(3)
G
G
S
sfc
cm
=
+
8
(4)
where S is the storage term, G
8cm
is the soil heat flux at 8 cm, and G
sfc
is the
soil heat flux at the surface.
6.5 In-Situ Calibration Theory
For detailed information on the theory of the in-situ calibration, see the Theory
section of the Hukseflux manual or visit the application section of the
Hukseflux web site at
Equation 6 in the Hukseflux manual is used to compute a new calibration every
three hours. The heater is on for a total of 180 seconds. TABLE 6-8 lists the
variables used in the Hukseflux manual and those in the example datalogger
programs.
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