Campbell Bowen Ratio Instrumentation, Инструкция по эксплуатации

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Section 4. Calculating Fluxes Using SPLIT
4-2
heat of the soil and the change in soil temperature,
∆
T
s
, over the output interval, t,
are required to calculate the stored energy.
The heat capacity of the soil is calculated by adding the specific heat of the dry
soil to that of the soil water. The values used for specific heat of dry soil and
water are on a mass basis. The heat capacity of the moist is given by:
( )
C C C C C
s b d m w b d v w w
= + = + ρ θ ρ θ ρ
(9)
θ
ρ
ρ
θ
m
w
b
v
=
(10)
where C
S
is the heat capacity of moist soil,
ρ
b
is bulk density,
ρ
w
is the density
of water, C
d
is the heat capacity of a dry mineral soil,
θ
m
is soil water content
on a mass basis,
θ
v
is 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
CS615 soil water content reflectometer. The value used for the heat capacity
of dry soil in the example SPLIT parameter file is a reasonable value for most
mineral soils (Hanks and Ashcroft, 1980).
The storage term is then given by Eq. (3).
S
T C d
t
s s
=
∆
(11)
Atmospheric pressure is a site-specific input. Pressure can be measured at the
site or obtained from a local meteorological station. An estimate of pressure
can be calculated for the site using a standard atmosphere with the following
equation:
P
E
= −
⎡
⎣⎢ ⎤
⎦⎥
101325 1
44307 69231
5.25328
.
.
(12)
where P is in kPa and the elevation, E, is in meters (Wallace and Hobbs, 1977).