The023/CO2 BOWEN RATIO SYSTEM WITH CO2 FLUX is warranted
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workmanship under nor mal use and service for twelve (12) months from date of
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023/CO2 BOWEN RATIO SYSTEM WITH CO2 FLUX
TABLE OF CONTENTS
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PAGE
SECTION 1. SYSTEM OVERVIEW
1.1Review of Theory ....................................................................................................................1-1
By analogy with molecular diffusion, the fluxgradient approach to vertical transport of an
entity from or to a surface assumes steady
diffusion of the entity along its mean vertical
concentration gradient.
When working within a few meters of the
surface, the water vapor flux density, sensible
heat flux, and carbon dioxide flux density, E, H,
may be expressed as:
and F
c
∂ρ
=
Ek
=ρ
HCk
Fk
cc
where
carbon dioxide density, C
air, T is temperature, z is height, and k
are the eddy diffusivities for vapor, heat, and
k
c
carbon dioxide respectively. Air density and the
specific heat of air should account for the
presence of water vapor. The eddy diffusivities
are functions of height. The vapor and
temperature gradients reflect temporal and
spatial averages.
Applying the Universal Gas Law to Eq. (1), and
using the latent heat of vaporization, λ, the
latent heat flux density, L
terms of mole fraction of water vapor (w).
Lk
ev
Here P is atmospheric pressure, R is the
universal gas constant, and M
weight of water. Similarly, Eq. (3) can be written
as:
Fk
cc
v
v
∂
z
∂
T
pH
∂
z
∂ρ
=
=λ
=
c
∂
z
is vapor density, ρ is air density,
ρ
v
PM
v
TRwz
∂
PMTRc
c
∂
∂
∂
z
is the specific heat of
p
, can be written in
e
is the molecular
v
is
ρ
c
, kH, and
v
(1)
(2)
(3)
(4)
(5)
where c is the mole fraction of carbon dioxide
and M
is the molecular weight of carbon
c
dioxide.
In practice, finite concentration gradients are
measured and an effective eddy diffusivity
assumed over the vertical gradient:
ev
=
HCk
ρ
TR
pH
PM
=
Lk
λ
PM
=
Fk
cc
TR
21
v
−
zz
()
12
−
TT
()
21
−
zz
()
12
−
cc
()
21
c
−
zz
()
12
(6)
(7)
(8)
−
ww
()
where the subscripts 1 and 2 refer to the upper
and lower arms respectively.
In general, k
and kH are not known but under
v
specific conditions are assumed equal. The
ratio of H to L
is then used to partition the
e
available energy at the surface into sensible and
latent heat flux. This technique was first
proposed by Bowen (1926). The Bowen ratio,
, is obtained from Eq. (6) and Eq. (7),
β
H
β
==
L
e
C
λε
−
TT
()
p
21
−
ww
()
21
(9)
where ε is the ratio of the molecular weight of
water vapor to dry air. The surface energy
budget is given by,
−=+,(10)
RGHL
ne
where R
is the total soil heat flux. R
into the surface and G, H, and L
away from the surface. Substituting βL
Eq. (10) and solving for L
L
e
is net radiation for the surface and G
n
−
RG
n
=
+1β
.(11)
and Fc are positive
n
e
yields:
e
are positive
for H in
e
1-1
SECTION 1. SYSTEM OVERVIEW
FIGURE 1.2-1 Vapor Measurement System
Sensible heat flux is found by substituting Eq.
(11) into Eq. (10) and solving for H.
=−−(12a)
HR GLE
n
=−−
HR G
n
RG
If the eddy diffusivity for carbon dioxide, k
assumed equal to k
−
n
+
1β
v (kH
), Fc can be found
(12b)
, is
c
using Eq. (13) and (8).
−
zz
()
12
=
k
c
TT
()
21
Measurements of R
−
H
C
ρ
p
and G, and the gradients
n
(13)
of w, T, and c are required to estimate latent
and sensible heat, and carbon dioxide flux.
Atmospheric pressure is also a necessary
variable, however, it seldom varies by more
than a few percent. It may be calculated for the
site, assuming a standard atmosphere, or
obtained from a nearby station and correcting
for any elevation difference.
The following equation can be used to estimate
the site pressure if the elevation is known:
PE=−
..
101325 1
44307 69231
5.25328
(14)
where P is in kPa and the elevation, E, is in
meters (Wallace and Hobbes, 1977).
Eq. (9) shows that the sensitivity of β is directly
related to the measured gradients; a 1% error in
a measurement results in a 1% error in β.
When the Bowen ratio approaches -1, the
calculated fluxes approach infinity. Fortunately,
this situation usually occurs during early
morning and late evening when the flux
changes direction and there is little available
energy, R
-1 (e.g., -1.25 < β < -0.75), L
- G. In practice, when β is close to
n
and H are
e
assumed to be negligible and are not
calculated. Ohmura (1982) describes an
objective method for rejecting erroneous Bowen
ratio data.
1.2 SYSTEM DESCRIPTION
1.2.1 WATER VAPOR AND CARBON DIOXIDE
MEASUREMENTS
Carbon dioxide and water vapor concentrations
are measured with a single Infrared Gas
Analyzer (Model LI-6262, LI-COR Inc., Lincoln,
NE) (IRGA), using a technique developed for
multiple level gradient studies (Lemon, 1960).
Air samples from two heights are routed to the
IRGA (Figure 1.2-1). The IRGA continuously
measures the gradient between the two levels.
1-2
CR23X
SECTION 1. SYSTEM OVERVIEW
FIGURE 1.2-2. Thermocouple Configuration
Inverted Teflon filters (Gelman, ACRO50) with a
1 µm pore size prevent dust contamination of
lines and IRGA. They also prevent liquid water
from entering the system.
A single low power DC pump aspirates the
system. Manually adjustable flow meters are
used to adjust and match the flow rates. A flow
rate of 0.4 liters/minute is recommended. A
CR23X datalogger measures all sensors and
controls the valves that switch air streams
through the IRGA.
Every two minutes the air drawn through the
IRGA is reversed with the first valve. Forty
seconds is allowed for the pump to purge the
IRGA. One minute and 20 seconds of
measurements are made and averaged for
each two minute cycle.
The carbon dioxide and water vapor gradients
are measured every second. The average
carbon dioxide and water vapor gradients are
calculated every 20 minutes. At the top of every
hour the sample cell in the IRGA is scrubbed of
carbon dioxide and water vapor. The absolute
concentration of carbon dioxide and water vapor
is then measured by the IRGA.
1.2.2 AIR TEMPERATURE MEASUREMENT
The air temperature gradient is measured with
fine wire chromel–constantan thermocouples.
The thermocouples are wired into the
datalogger such that the temperature gradient is
measured differentially (Figure 1.2-2). The
differential voltage is due to the difference in
temperature between T
and T2 and has no
1
inherent sensor offset error. The datalogger
resolution is 0.006°C with 0.1 µV rms noise.
The thermocouples are not aspirated.
Calculations indicate that a 25 µm (0.001 in)
diameter thermocouple experiences less than
-1
0.2°C and 0.1°C heating at 0.1 m s
-1
1 m s
W m
wind speeds, respectively, under 1000
-2
solar radiation (Tanner, 1979). More
and
importantly, error in the gradient measurement
is due only to the difference in the radiative
heating of the two thermocouple junctions. The
physical symmetry of the thermocouple junction
minimizes this error. Conversely, contamination
of only one junction can cause large errors. A
pair of 76 µm (0.003 in) thermocouples with two
parallel junctions at each height are used to
make the temperature gradient measurement
Applying temperature gradients to the
thermocouple connectors was found to cause
offsets. The connector mounts were designed
with radiation shields and thermal conductors to
minimize gradients.
1.2.3 NET RADIATION AND SOIL HEAT FLUX
Net radiation and soil heat flux are averaged
over the same time period as the water vapor,
temperature, and carbon dioxide gradient.
To measure soil heat flux, heat flux plates are
buried in the soil at a depth of eight centimeters.
The average temperature of the soil layer above
the plate is measured using four parallel
thermocouples. The heat flux at the surface is
1-3
SECTION 1. SYSTEM OVERVIEW
then calculated by adding the heat flux
measured by the plate to the energy stored in
the soil layer. The storage term is calculated by
multiplying the change in soil temperature over
the averaging period by the soil heat capacity.
1.2.4. POWER SUPPLY
The current requirements of the components of
the 023/CO2 Bowen Ratio system are given in
Table 1.2-1.
TABLE 1.2-1. Component Power
Requirements
CURRENT
COMPONENTat 12 VDC
LI-62621000 mA
Pump60 mA
CR23X5 mA
Two large solar panels (60 watts or greater) and
a 70 amp-hour battery are capable of providing
a continuous current of 1.1 A, assuming 1000
-2
of incoming solar radiation for 12 hours a
Wm
day. The solar panels are required to keep a
full charge on the battery. The voltage of the
battery must be monitored by the station
operator. Do not allow the battery voltage to fall
below 11 VDC. If the battery voltage falls below
11 VDC, the IRGA will shut down. The station
operator must then manually reset the IRGA by
turning the power switch (on the front panel) off
and then on. A datalogger control port is used
to control power to the pump via relays.
1-4
SECTION 2. LI-6262 INSTALLATION
This section describes how the LI-6262 Infrared Gas Analyzer is integrated into the 023/CO2 enclosure.
ZEROSPAN
0
0
1
28
2
27
3
26
4
25
5
24
6
23
7
22
8
21
9
20
10
19
11
18
12
17
13
16
14
15
ZEROSPAN
0
0
1
28
2
27
3
26
4
25
5
24
6
23
7
22
8
21
9
20
10
19
11
18
12
17
13
16
14
15
0
0
28
27
26
25
24
23
22
21
20
19
18
17
16
15
0
0
28
27
26
25
24
23
22
21
20
19
18
17
16
15
CO /
1
2
3
4
5
6
7
8
9
CO
10
11
12
13
14
1
2
3
4
5
6
7
8
9
H O
10
2
11
12
13
14
H O ANALYZER
22
Model LI-6262
2
C2C2mV
m/m
LI-COR
339.48
R
ON
-5.250
123
FUNCTION
456
EXIT
789
0
ENTER
C
READYOFF
+12V
GROUND
GROUND
SOL 1+
SOL 1GROUND
SOL 2+
SOL 2GROUND
PUMP+
PUMPGROUND
MIRROR+
MIRRORGROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON
BR RELAY DRIVER-12V
MADE IN USA
FIGURE 2-1. 023/CO2 Bowen Ratio System
2.1 ANALYZER PREPARATION
The LI-6262 has two inline Balston filters inside the
analyzer, ahead of the reference and sample cells.
These filters have high flow rates with low back
pressure. However, they have a time constant of
about a minute. To decrease the time constant of
the analyzer, replace the Balston filters with tubing.
The ACRO50 filters installed on the Bowen Ratio
arms will provide sufficient filtration for the LI-6262.
Section 7.5 of the LI-6262 manual provides more
information on removing the Balston filters.
CAUTION: Never operate the LI-6262
without adequate filtration ahead of the
reference and sample cells.
2.2 INITIAL SETUP
The LI-6262 is mounted on top of the black
bracket inside the 023/CO2 enclosure. It is held
in place by two mounting rails that are attached
to the bottom of the analyzer by four pan head
screws (Figure 2.2-1). It may be necessary to
relocate the rubber feet of the LI-6262 so they
do not interfere with the black mounting bracket.
MADE IN USA
+12V
GROUND
GROUND
SOL 1+
SOL 1GROUND
SOL 2+
SOL 2GROUND
PUMP+
PUMPGROUND
MIRROR+
MIRRORGROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON
BR RELAY DRIVER-12V
CC / MIN.
AIR
X 100
10
8
6
4
2
REFERENCEREFERENCE
12
34
56
78
910
SE
1
2
3
4
HL
HL
HL
HL
HL
DIFF
1314
1516
1718
1920
2122
SE
7
8
9
40
HL
HL
HL
HL
HL
DIFF
04:REF_TEMP
+21.93
CR23X MICROLOGGER
CS I/O
CC / MIN.
AIR
X 100
10
8
6
4
2
SAMPLESAMPLE
1112
5
6
EX1
EX2
EX3
EX4
CAO1
CAO2P1P2P3P4
11
HL
2324
12
HL
COMPUTER
RS232
POWER OUTCONTROL I/O
G5VG
SW12G12V
12VGC1C2C3C4GC5C6C7C8
SDM
1 2 3 A
4 5 6 B
7 8 9 C
0 # D
*
G 12V
POWER IN
G
GROUND
LUG
SN:
MADE IN USA
The 023/CO2 Bowen Ratio system requires that
the LI-6262 operate in differential mode (see
the LI-6262 manual for details). In this mode
carbon dioxide and water vapor are scrubbed
on the chopper input.
Prepare a soda lime and desiccant tube, as
described in Section 7.4 of the LI-6262 manual.
The bevaline tube that connects the soda lime
and desiccant tube to the LI-6262 chopper must
be replaced with longer tubes, to accommodate
mounting the desiccant tube to the enclosure
backplate. Attach the bottom hose (nearest the
soda lime) to the FROM CHOPPER fitting and
the top hose (nearest the perchlorate) to the TO
CHOPPER fitting (Figure 2.2-2). Install the tube
in the enclosure using the two clips mounted on
the left side of the backplate.
Every hour the sample cell of the analyzer is
scrubbed of carbon dioxide and water vapor
with external soda lime and desiccant tubes.
The absolute concentration of carbon dioxide
and water vapor is then measured by the
analyzer. The soda lime and desiccant tubes
are plumbed in series and are integrated into
2-1
SECTION 2. LI-6262 INSTALLATION
CO
2
H O
2
CO /2H O2ANALYZER
Model LI-6262
LI-COR
ON
OFF
FUNCTION
EEX
ENTER
CC / MIN.
AIR
X 100
10
8
6
4
2
CC / MIN.
AIR
X 100
10
8
6
4
2
REFERENCESAMPLE
+12V
GROUND
GROUND
SOL 1+
SOL 1GROUND
SOL 2+
SOL 2GROUND
PUMP +
PUMP GROUND
MIRROR +
MIRROR GROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON
BR RELAY DRIVER -12V
MADE IN USA
+12V
GROUND
GROUND
SOL 1+
SOL 1GROUND
SOL 2+
SOL 2GROUND
PUMP +
PUMP GROUND
MIRROR +
MIRROR GROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON
BR RELAY DRIVER -12V
MADE IN USA
123A
456B
789C
*
0#D
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DAC1 5V
DAC1 100mV
DAC1 20mA
SIG GND
DAC2 5V
DAC2 100mV
DAC2 20mV
SIG GND
CO 1S
H O 1S
TEMP 5V
SIG GND
AUX INPUT
CHASSIS GND
2
CO 4S
2
2
H O 4S
2
115
RS-232C DCESAMPLEREFERENCE
IN
OUT
SCRUBBER TO
CHOPPER
AC
VOLTAGE
.25A/230V
.5A/115V
FROM
CHOPPER
10.5-16 VDC
2A
UNPLUG AC POWER BEFORE SERVICING TO PREVENT PERSONAL INJURY
WARNING!
LI-6262
CO /H O ANALYZER
2
2
MODEL
SR. NO.
LI-COR
U.S. Patent # 4,803,370
U.S. and Foreign Patents Pending
Made in U.S.A.
IRG3-2 2 9
LI-6262 Maintenance
Internal soda Lime/Desiccant must be
changed annually.
A range of time periods are given for
maintenance. Actual time period depends
on operating conditions.
External Soda Lime/Desiccant: weekly,
monthly
Internal Air Filters: monthly, yearly
Fan Air Filter: weekly, monthly
Factory Checkout: yearly
See operator's maunal for servicing
Internal components.
the system with a pair of quick connect
connectors.
Fill the tube with the female connector with soda
lime and the tube with the male connector with
magnesium perchlorate. Plumb the tubes as
shown in Figure 2.2-3. The tubes are attached
to the backplate with two pair of clips.
The analyzer's analog output is connected to
the CR23X datalogger with the 023/CO2 signal
cable. Table 2.2-1 describes the connections
on the analyzer end of the signal cable. Table
3.3-1 (Section 3) describes the connections on
the CR23X end of the cable.
After the analyzer is plumbed and wired into the
023/CO2 system and the mounting rails are
fastened to the analyzer, slide the analyzer over
the black bracket as shown in Figure 2.2-1.
Line the push buttons with the holes on either
side of the bracket and press firmly until the
analyzer is seated on the bracket. Push the
buttons in until a click is heard and LI-6262 is
securely attached to the black bracket.
NOTE: The analyzer fits snugly within the
fiberglass enclosure. The zero and span
knobs will make contact with the inside of
the enclosure lid. With time, four black
rings will appear on the lid. The zero and
span knobs are not exposed to any
excessive stress when the lid is closed and
latched.
FIGURE 2.2-1. LI-6262 and Mounting
Hardware
2-2
To Sample Flowmeter
To Valve B
To Reference Flowmeter
To Zero Switch
FIGURE 2.2-2. Plumbing Inputs
Mount on Back Plate
To 12 VDC 70
Ahr (or greater)
Battery
Magnesium
Perchlorate
Fiberglass Wool
Soda Lime
Zero Switch
SECTION 2. LI-6262 INSTALLATION
Valve B
SOL 2-
To Sample In
SOL 2+
Upper Arm
To Reference In
Valve A
SOL 1-
Magnesium
Perchlorate
SOL 1+
Lower Arm
Soda Lime
CO2PUMB(system)
FIGURE 2.2-3. 023/CO2 Plumbing, Valves, and Soda Lime and Desiccant Tubes
2-3
SECTION 3. STATION INSTALLATION
ers
Figure 3-1 shows the typical 023/CO2 system installed on a CM10 tripod. The 023/CO2 enclosure and
mounting arms mount to the tripod mast (1 1/2 in. pipe) with U-bolts. The size of the tripod allows the
heights of the arms to be adjusted from 0.5 to 3 meters. The mounting arms should be oriented due
south to avoid partial shading of the thermocouples.
Two solar panels (60 watts or greater) are mounted on a separate tripod or A-frame (not provided by
Campbell Scientific). The net radiometer is mounted on a separate stake (not provided by Campbell
Scientific). It should be positioned so that it is never shaded by the tripod and mounting hardware, and
such that the mounting hardware is not a significant portion of its field of view.
Other Sensors Not Shown:
(1) Wind Speed and Direction
Sensor
(1) Air Temperature and
Humidity Sensor
BOWENCO2(system)
Intake
Filt
023/CO2 Enclosure
Type E Fine
Wire
Thermocouples
Averaging Soil
Temperature
Probe and Soil
Heat Flux Plates
Net Radiometer
CM10 Tripod
Grounding Rod
User Supplied deep cycle
battery (70 AHr or greater).
Two Solar Panels, 60 watts or
greater (not shown).
FIGURE 3-1. 023/CO2 Bowen Ratio System with CO2 Flux
3-1
SECTION 3. STATION INSTALLATION
3.1 SENSOR HEIGHT AND
SEPARATION
There are several factors which must be
balanced against each other when determining
the height at which to mount the support arms
for the thermocouples and air intakes.
The differences in moisture, temperature, and
carbon dioxide increase with height, thus the
resolution of the gradient measurements
improves with increased separation of the arms.
The upper mounting arm must be low enough
that it is not sampling air that is coming from a
different environment up wind. The air that the
sensors see must be representative of the
soil/vegetation that is being measured. As a
rule of thumb, the surface being measured
should extend a distance upwind that is at least
100 times the height of the sensors. The
following references discuss fetch requirements
in detail: Brutsaert (1982); Dyer and Pruitt
(1962); Gash (1986); Schuepp, et al. (1990);
and Shuttleworth (1992).
The lower mounting arm needs to be higher
than the surrounding vegetation so that the air it
is sampling is representative of the bulk crop
surface, and not a smaller surface i.e. do not
place the lower arms in between the rows of a
row crop like sorghum.
The example SPLIT parameter file that
calculates the surface fluxes assumes a 1.0
meter arm separation. If your station is installed
with an arm separation other than 1.0 meter,
measure and note the separation. Be sure to
change the arm separation, DZ, in the SPLIT
parameter file CALBRC.PAR.
3.2 SOIL THERMOCOUPLES AND HEAT
FLUX PLATES
The soil thermocouples and heat flux plates are
installed as shown in Figure 3.2-1. The TCAV
parallels four thermocouples together to provide
the average temperature, see Figure 3.2-2. It is
constructed so that two thermocouples can be
used to obtain the average temperature of the
soil layer above one heat flux plate and the
other two above the second plate. The
thermocouple pairs may be up to two meters
apart.
The location of the two heat flux plates and
thermocouples should be chosen to be
representative of the area under study. If the
ground cover is extremely varied, it may be
necessary to have additional sensors to provide
a valid average.
Use a small shovel to make a vertical slice in
the soil and excavate the soil to one side of the
slice. Keep this soil intact so that it can be
replaced with minimal disruption.
The sensors are installed in the undisturbed
face of the hole. Measure the sensor depths
from the top of the hole. Make a horizontal cut
eight cm below the surface with a knife into the
undisturbed face of the hole and insert the heat
flux plate into the horizontal cut. Press the
stainless steel tubes of the TCAVs above the
plates as shown in Figure 3.2-1. When
removing the thermocouples, grip the tubing,
not the thermocouple wire.
Install the CS615 as shown in Figure 3.2-1.
See the CS615 manual (Section 5) for detailed
installation instructions.
3-2
Up to 1 m
2.5 cm
Partial emplacement of the HFT3 and the TCAV
sensors is shown for illustration purposes. All
sensors must be completely inserted into the soil face
before the hole is backfilled.
6 cm
2 cm
Ground Surface
8 cm
FIGURE 3.2-1. Placement of Thermocouples and Heat Flux Plates
FIGURE 3.2-2. TCAV Spatial Averaging
Thermocouple Probe
Never run the leads directly to the surface.
Rather, bury the sensor leads a short distance
back from the hole to minimized thermal
conduction on the lead wires. Replace the
excavated soil back into its original position
after the TCAVs are installed.
SECTION 3. STATION INSTALLATION
3.4 BATTERY CONNECTIONS
Two terminal strip adapters for the battery posts
(P/N 4386) are provided with the 023/CO2
(Figure 3.4-1). These terminal strips will mount
to the wing nut battery posts on most deep cycle
lead acid batteries.
The solar panels (60 watts or greater), BR relay
driver, LI-6262, and CR23X each have separate
power cables. Once the system is installed,
these power cables are then connected to the
external battery (red to positive, black to
negative). The CR23X power cable is shipped
in the 023/CO2 enclosure and must be
connected to the +12V (red from power cable)
and ground (black from power cable) terminals
on the CR23X wiring panel.
Several deep cycle batteries can be connected
in parallel, to provide power to the system
during cloudy or overcast days.
Finally, wrap the thermocouple wire around the
CR23X base at least twice before wiring them
into the terminal strip. This will minimized
thermal conduction into the terminal strip. After
all the connections are made, replace the
terminal strip cover.
3.3 WIRING
Table 3.3-1 lists the connections to the CR23X
for the standard 023/CO2 system using the
example program in Section 4. Because the air
temperature measurements are so critical, the
air temperature thermocouples are connected
to channel 4 (the channel that is closest to the
reference temperature thermistor). The input
terminal strip cover for the CR23X must be
installed once all connections have been made
and verified (Section 13.4.1 of the CR23X
manual).
Finally, wrap the thermocouple wire around the
CR23X base at least twice before wiring them
into the terminal strip. This will minimized
thermal conduction into the terminal strip. After
all the connections are made, replace the
terminal strip cover.
FIGURE 3.4-1. Terminal Strip Adapters for
Connections to Battery
The LI-6262 can not be turned on and off with
relays without a hardware modification to the
power board (contact LI-COR for details). After
the hardware modification has been made. A
Crydom D1D07 (P/N 7321) can be used to
power the LI-6262. The control side of the
D1D07 can be operated by a BR relay driver.
Do not power the LI-6262 through the BR relay
driver, because there is a 0.8 V drop through it
and the high current drain of the LI-6262 may
create an offset in single ended measurements.
3-3
SECTION 3. STATION INSTALLATION
TABLE 3.3-1. CR23X/Sensor Connections for Example Program
AND LOWER ARM TO SAMPLEBLUE w/ WHITE
C3PULSE TO END SCRUBWHITE w/ ORANGE
C4PULSE TO SCRUBWHITE w/ BLUE
3-4
SECTION 3. STATION INSTALLATION
C5PULSE TO TURN ON PUMPGREEN w/ WHITE
(SET FLAG 5 AND 6; RESET FLAG 5)WHITE w/ GREEN
C6PULSE TO TURN OFF PUMPBROWN w/ WHITE
(SET FLAG 5; RESET FLAG 6 AND 5)WHITE w/ BROWN
C7CS615 (Control)ORANGE
GGROUND WIRECLEAR
3-5
SECTION 4. SAMPLE 023/CO2 PROGRAM
4.1 PROGRAM DETAILS
4.1.1 SCRUBBING THE SAMPLE CELL
The signal from the analyzer is proportional to
the difference in concentration between the
reference and sample cells. If the reference
concentration, C
concentration in the sample cell can be found
using the relationship below,
=+
CVGV
f(15)
()
sr
where the function f is a fifth order polynomial of
the form
=+ + + +(16)
f(V)AV BVCVDVEV
with coefficients A, B, C, D, and E that are
unique to each analyzer, C
concentration in the sample cell, V is the
analyzer output, V
analyzer if there was zero concentration in the
reference cell and a known concentration, C
the sample cell, T and T
temperature and calibration temperature, P and
are the ambient and calibration (sea level)
P
o
pressures, and G is given by:
−
KV
=
G
r
K
where K is a calibration constant.
Every hour the sample cell is scrubbed of
carbon dioxide and water vapor. The absolute
concentration of carbon dioxide and water vapor
can then be calculated. Scrubbing the sample
cell and leaving the reference cell at ambient
avoids the zero offset shift that occurs when the
concentration in the reference cell changes.
The equations presented in the LI-6262 manual
are for the case when the concentration in the
reference cell is known (scrubbed) and the
concentration in sample cell is unknown. Since
the 023/CO2 system scrubs the sample cell, the
equations must be reformulated.
When the sample cell is scrubbed the
concentration C
the following is true,
+=0(18)
VG V
r
, is known, the absolute
r
P
T
o
P
T
o
2345
is the gas
S
is the signal output from the
r
are the analyzer
o
in Eq. (13) is equal to zero and
S
, in
r
(17)
VVG
=−.(19)
r
Substituting Eq. (17) into (15) and solving for G
yields the relationship below.
K
G
=
KV
−
Now substitute Eq. (18) into (17).
VK
=−
V
r
V
r
−
KV
is the signal the analyzer would output if the
reference cell was scrubbed instead of the
sample cell. The value found from Equation
(21) is used in the fifth order polynomial to find
the absolute concentration of carbon dioxide
and water vapor. New values of V
and G are
r
calculated every hour and used in measuring
the carbon dioxide and water vapor gradient.
The absolute concentration of water vapor and
carbon dioxide are not corrected for T/To
online. Thus, during a scrub, the absolute
concentrations displayed by the LI-6262 will
differ by a factor of T/To to those calculated by
the CR23X.
4.1.2 COEFFICIENTS
The unique calibration coefficients for the
LI-6262 must be entered in the CR23X
program. The calibration temperature (Kelvins)
and K coefficients are entered in Subroutine 1.
The polynomial coefficients A (C1), B (C2), C
(C3), D (C4), and E (C5) are entered in
Subroutine 7.
The magnitude of the coefficients that can be
entered into the polynomial instruction
(Instruction 55) is 0.00001 to 99999. Since the
coefficients are outside this range, they must be
prescaled. The input to the polynomial is
-3
multiplied by 10
by the first instruction in
Subroutine 7. The coefficients, as they are
given by LI-COR, must be transformed in order
to enter them into the program. To perform the
carbon dioxide and water vapor coefficient
transformation; multiply the A (C1) coefficient by
3
, the B (C2) coefficient by 106, the C (C3)
10
coefficient by 10
12
, and the E (C5) coefficient by 1015. Table
10
9
, the D (C4) coefficient by
4.1-1 provides and example of how to transform
typical LI-6262 water vapor coefficients.
(20)
(21)
4-1
SECTION 4. SAMPLE 023/CO2 PROGRAM
TABLE 4.1-1. Example LI-6262 Carbon Dioxide Coefficients
CoefficientCoefficient
(LI-COR)LI-6262
A0.1505310
B7.0875 x 10
C8.4794 x 10
D-1.1482 x 10
E7.5212 x 10
-6
-9
-12
-17
Multiply byCR23X(CSI)
10
10
10
10
3
6
9
12
15
150.53C1
7.0875C2
8.4794C3
-1.1482C4
0.07512C5
4.2 CR23X PROGRAM
A copy of the example program for the CR23X is available on the Campbell Scientific ftp site at
ftp://ftp.campbellsci.com/pub/outgoing/files/br_co2.exe. Br_co2.exe is a self extracting file. At a DOS
prompt, type in br_co2.exe and press the <enter> key. Use EDLOG to edit the example program. Table
4.2-2 lists the outputs from the example program.
TABLE 4.2-1. Example Datalogger Program
;{CR23X}
;
;c:\dl\co2\co2feb98.csi
;23 February 1998
;Example CR23X program for the 023/CO2 Bowen ratio system w/ CO2 Flux.
;Flag 1 - When HIGH stops averaging during scrubbing or manual
;control of flow valves. When LOW Subroutine 1 loads
;constants.
;Flag 2 - When HIGH the upper arm is routed into the sample input
;and the lower arm into the reference, when LOW the
;upper arm is routed into the reference and the lower
;arm into the sample.
;Flag 3 - When HIGH timing out for forty seconds after switching
;upper and lower levels.
;Flag 4 - Is set HIGH during automatic and manual scrub.
;Flag 5 - When HIGH allows manual control of flow valves and turning
;the pump on and off. Use Flag 2 to toggle the valve
;and Flag 6 to operate the pump.
;Flag 6 - When HIGH the pump is on, When LOW the pump is off.
;Flag 7 - Used in Subroutine 7 to determine which polynomial to use.
;Flag 8 - Set HIGH to perform a manual scrub.
*Table 1 Program
01:1Execution Interval (seconds)
;Make measurements.
01:Internal Temperature (P17)
1:35Loc [ refrnc ]
4-2
02:Thermocouple Temp (SE) (P13)
1:1Reps
2:2110 mV, 60 Hz Reject, Slow Range
3:8In Chan
4:2Type E (Chromel-Constantan)
5:35Ref Temp Loc [ refrnc ]
6:33Loc [ lwr_TC ]
7:1Mult
8:0Offset
03:Thermocouple Temp (Diff) (P14)
1:1Reps
2:2110 mV, 60 Hz Reject, Slow Range
3:4In Chan
4:2Type E (Chromel-Constantan)
5:33Ref Temp Loc [ lwr_TC ]
6:32Loc [ upr_TC ]
7:1Mult
8:0Offset
04:Z=X-Y (P35)
1:33X Loc [ lwr_TC ]
2:32Y Loc [ upr_TC ]
3:34Z Loc [ del_TC ]
3:10Set Output Flag High
32:Set Active Storage Area (P80)
1:3Input Storage
2:13Loc [ avg_Ts ]
33:Average (P71)
1:1Reps
2:7Loc [ Ts ]
34:If Flag/Port (P91)
1:10Do if Output Flag is High (Flag 0)
2:30Then Do
4-10
;Find the change in soil temperature.
;
35:Z=X-Y (P35)
1:13X Loc [ avg_Ts ]
2:12Y Loc [ prv_Ts ]
3:14Z Loc [ del_Ts ]
36:Z=X (P31)
1:13X Loc [ avg_Ts ]
2:12Z Loc [ prv_Ts ]
;Apply the temperature correction to
;the soil moisture measured by the CS615,
;if the soil temperature is in the range of
;10 degrees C to 30 degrees C. See Section
;4.3.4 of the CS615 manual for more information.
;
37:If (X<=>F) (P89)
1:13X Loc [ avg_Ts ]
2:3>=
3:10F
4:30Then Do
SECTION 4. SAMPLE 023/CO2 PROGRAM
38:If (X<=>F) (P89)
1:13X Loc [ avg_Ts ]
2:4<
3:30F
4:30Then Do
39:Z=X+F (P34)
1:13X Loc [ avg_Ts ]
2:-20F
3:65Z Loc [ D ]
40:Polynomial (P55)
1:1Reps
2:69X Loc [ s_wtr_o ]
3:66F(X) Loc [ E ]
4:-.0346C0
5:1.9C1
6:-4.5C2
7:0C3
8:0C4
9:0C5
41:Z=X*F (P37)
1:66X Loc [ E ]
2:.01F
3:66Z Loc [ E ]
42:Z=X*Y (P36)
1:65X Loc [ D ]
2:66Y Loc [ E ]
3:65Z Loc [ D ]
4-11
SECTION 4. SAMPLE 023/CO2 PROGRAM
43:Z=X-Y (P35)
1:69X Loc [ s_wtr_o ]
2:65Y Loc [ D ]
3:70Z Loc [ s_wtr_o_T ]
44:Else (P94)
;Do not apply temperature correction if the
;soil temperature is outside the range of
;10 degrees C to 30 degrees C.
;
45:Z=X (P31)
1:69X Loc [ s_wtr_o ]
2:70Z Loc [ s_wtr_o_T ]
46:End (P95)
47:Else (P94)
;Do not apply temperature correction if the
;soil temperature is outside the range of
;10 degrees C to 30 degrees C.
;
48:Z=X (P31)
1:69X Loc [ s_wtr_o ]
2:70Z Loc [ s_wtr_o_T ]
49:End (P95)
50:End (P95)
;Generate energy balance and meteorological
;output array every twenty minutes.
;
51:If Flag/Port (P91)
1:10Do if Output Flag is High (Flag 0)
2:10Set Output Flag High
52:Set Active Storage Area (P80)
1:1Final Storage
2:22Array ID
53:Real Time (P77)
1:1110Year,Day,Hour/Minute
54:Resolution (P78)
1:1High Resolution
55:Average (P71)
1:6Reps
2:1Loc [ HMP_T ]
56:Sample (P70)
1:2Reps
2:13Loc [ avg_Ts ]
4-12
57:Sample (P70)
1:1Reps
2:8Loc [ rh_frac ]
58:Average (P71)
1:1Reps
2:9Loc [ battry ]
59:Wind Vector (P69)
1:1Reps
2:60Samples per Sub-Interval
3:00S, qu, & s(qu) Polar
4:16Wind Speed/East Loc [ wnd_spd ]
5:17Wind Direction/North Loc [ wnd_dir ]
60:Sample (P70)
1:3Reps
2:68Loc [ cs615_mso ]
*Table 3 Subroutines
SECTION 4. SAMPLE 023/CO2 PROGRAM
;Scrub.
01:Beginning of Subroutine (P85)
1:1Subroutine 1
02:If Flag/Port (P91)
1:21Do if Flag 1 is Low
2:30Then Do
;Enter the CO2 calibration
;temperature (Kelvin).
;
03:Z=F (P30)
1:1F
2:0Exponent of 10
3:54Z Loc [ To_co2 ]
;Enter the H2O calibration
;temperature (Kelvin).
;
04:Z=F (P30)
1:1F
2:0Exponent of 10
3:55Z Loc [ To_h2o ]
;Enter the K coefficient for CO2.
;
05:Z=F (P30)
1:1F
2:0Exponent of 10
3:56Z Loc [ K_co2 ]
;To(CO2) <- unique value
;To(H2O) <- unique value
;K(CO2) <- unique value
4-13
SECTION 4. SAMPLE 023/CO2 PROGRAM
;Enter the K coefficient for H2O.
;
06:Z=F (P30)
1:1F
2:0Exponent of 10
3:57Z Loc [ K_h2o ]
;Enter the local pressure in kPa.
;
07:Z=F (P30)
1:1F
2:0Exponent of 10
3:23Z Loc [ P_kPa ]
;Location 43 = Po/(P*1000)
;
08:Z=F (P30)
1:.10132 F
2:0Exponent of 10
3:43Z Loc [ Po_P_1000 ]
09:Z=X/Y (P38)
1:43X Loc [ Po_P_1000 ]
2:23Y Loc [ P_kPa ]
3:43Z Loc [ Po_P_1000 ]
;K(H2O) <- unique value
;P(kPa) <- unique value
10:Do (P86)
1:11Set Flag 1 High
;During first pass switch the upper arm
;into the reference cell, the lower arm
;into the sample cell, and set the
;scrub valve.
;
11:Do (P86)
1:42Set Port 2 High
12:Do (P86)
1:44Set Port 4 High
13:Do (P86)
1:22Set Flag 2 Low
14:Do (P86)
1:9Call Subroutine 9
15:End (P95)
16:Z=Z+1 (P32)
1:46Z Loc [ scrub_ctr ]
;Set all ports LOW
4-14
17:Volt (Diff) (P2)
1:2Reps
2:255000 mV, 60 Hz Reject, Fast Range
3:7In Chan
4:10Loc [ co2mV ]
5:1Mult
6:0Offset
18:Do (P86)
1:3Call Subroutine 3
19:If (X<=>F) (P89)
1:46X Loc [ scrub_ctr ]
2:3>=
3:50F
4:10Set Output Flag High
20:Set Active Storage Area (P80)
1:3Input Storage
2:10Loc [ co2mV ]
21:If (X<=>F) (P89)
1:46X Loc [ scrub_ctr ]
2:4<
3:40F
4:19Set Flag 9 High
SECTION 4. SAMPLE 023/CO2 PROGRAM
;Analyzer temperature
22:Average (P71)
1:2Reps
2:10Loc [ co2mV ]
23:Do (P86)
1:27Set Flag 7 Low
24:Beginning of Loop (P87)
1:0Delay
2:2Loop Count
25:Z=X-Y (P35)
1:56--X Loc [ K_co2 ]
2:10--Y Loc [ co2mV ]
3:26--Z Loc [ G_co2 ]
26:Z=X/Y (P38)
1:56--X Loc [ K_co2 ]
2:26--Y Loc [ G_co2 ]
3:26--Z Loc [ G_co2 ]
27:Z=X*Y (P36)
1:26--X Loc [ G_co2 ]
2:10--Y Loc [ co2mV ]
3:24--Z Loc [ Vr_co2_mV ]
28:Z=X*F (P37)
1:24--X Loc [ Vr_co2_mV ]
2:-1F
3:24--Z Loc [ Vr_co2_mV ]
4-15
SECTION 4. SAMPLE 023/CO2 PROGRAM
29:Z=X (P31)
1:24--X Loc [ Vr_co2_mV ]
2:41--Z Loc [ co2mVinpt ]
30:Do (P86)
1:7Call Subroutine 7
31:Z=X (P31)
1:28--X Loc [ co2_uM ]
2:21--Z Loc [ co2ref_uM ]
32:Z=X (P31)
1:18--X Loc [ Ta_To_co2 ]
2:62--Z Loc [ scb_Tao_C ]
33:Do (P86)
1:17Set Flag 7 High
34:End (P95)
;During the autoscrub make one pass
;through the calculation. During a
;manual scrub, pass through the
;calculation until Flag 8 is set Low.
;
1:1Reps
2:255000 mV, 60 Hz Reject, Fast Range
3:9In Chan
4:40Loc [ T_Anlyzr ]
5:.01221 Mult
6:0Offset
54:Z=X+F (P34)
1:40X Loc [ T_Anlyzr ]
2:273.15F
3:53Z Loc [ T_anlyr_K ]
55:Z=X/Y (P38)
1:53X Loc [ T_anlyr_K ]
2:54Y Loc [ To_co2 ]
3:18Z Loc [ Ta_To_co2 ]
56:Z=X/Y (P38)
1:53X Loc [ T_anlyr_K ]
2:55Y Loc [ To_h2o ]
3:19Z Loc [ Ta_To_h2o ]
57:End (P95)
4-17
SECTION 4. SAMPLE 023/CO2 PROGRAM
;Positive calibration and wind speed
;corrections.
58:Beginning of Subroutine (P85)
1:4Subroutine 4
59:Z=X*F (P37)
1:16X Loc [ wnd_spd ]
2:.2F
3:60Z Loc [ C ]
60:Z=X*F (P37)
1:60X Loc [ C ]
2:.066F
3:58Z Loc [ A ]
61:Z=X+F (P34)
1:60X Loc [ C ]
2:.066F
3:59Z Loc [ B ]
62:Z=X/Y (P38)
1:58X Loc [ A ]
2:59Y Loc [ B ]
3:61Z Loc [ corr_fac ]
63:Z=Z+1 (P32)
1:61Z Loc [ corr_fac ]
;Enter the positive multiplier (p.ppp).
;
64:Z=X*F (P37)
1:4X Loc [ Rn ]
2:1F
3:4Z Loc [ Rn ]
65:Z=X*Y (P36)
1:4X Loc [ Rn ]
2:61Y Loc [ corr_fac ]
3:4Z Loc [ Rn ]
66:End (P95)
;Negative calibration and wind speed
;corrections.
67:Beginning of Subroutine (P85)
1:5Subroutine 5
68:Z=X*F (P37)
1:16X Loc [ wnd_spd ]
2:.00174 F
3:58Z Loc [ A ]
;p.ppp <- unique value
4-18
69:Z=X+F (P34)
1:58X Loc [ A ]
2:.99755 F
3:61Z Loc [ corr_fac ]
;Enter the negative multiplier (n.nnn).
;
70:Z=X*F (P37)
1:4X Loc [ Rn ]
2:1F
3:4Z Loc [ Rn ]
71:Z=X*Y (P36)
1:4X Loc [ Rn ]
2:61Y Loc [ corr_fac ]
3:4Z Loc [ Rn ]
72:End (P95)
;Apply the LI-COR 6262 coefficient to
;CO2 and H2O.
73:Beginning of Subroutine (P85)
1:7Subroutine 7
SECTION 4. SAMPLE 023/CO2 PROGRAM
;n.nnn <- unique value
74:Z=X*Y (P36)
1:41--X Loc [ co2mVinpt ]
2:43Y Loc [ Po_P_1000 ]
3:41--Z Loc [ co2mVinpt ]
75:If Flag/Port (P91)
1:27Do if Flag 7 is Low
2:30Then Do
;Enter the A (C1), B (C2), C (C3),
;D (C4), and E (C5) coefficients for
;CO2 (see Section 4.1.2).
;
76:Polynomial (P55)
1:1Reps
2:41X Loc [ co2mVinpt ]
3:28F(X) Loc [ co2_uM ]
4:0C0
5:1C1
6:1C2
7:1C3
8:1C4
9:1C5
77:Else (P94)
;A <- unique value
;B <- unique value
;C <- unique value
;D <- unique value
;E <- unique value
4-19
SECTION 4. SAMPLE 023/CO2 PROGRAM
;Enter the A (C1), B (C2), C (C3),
;D (C4), and E (C5) coefficients for
;H2O (see Section 4.1.2).
;
78:Polynomial (P55)
1:1Reps
2:42X Loc [ h2omVinpt ]
3:29F(X) Loc [ h2o_mM ]
4:0C0
5:1C1
6:1C2
7:1C3
8:1C4
9:1C5
79:End (P95)
80:End (P95)
;Correct the sign on the gradients.
81:Beginning of Subroutine (P85)
1:8Subroutine 8
;A <- unique value
;B <- unique value
;C <- unique value
;D <- unique value
;E <- unique value
82:Z=X (P31)
1:30X Loc [ del_co2 ]
2:38Z Loc [ co2_corr ]
83:Z=X (P31)
1:31X Loc [ del_h2o ]
2:39Z Loc [ h2o_corr ]
84:Z=X (P31)
1:10X Loc [ co2mV ]
2:36Z Loc [ co2mVcorr ]
85:Z=X (P31)
1:11X Loc [ h2omV ]
2:37Z Loc [ h2omVcorr ]
86:If Flag/Port (P91)
1:12Do if Flag 2 is High
2:30Then Do
87:Beginning of Loop (P87)
1:0Delay
2:4Loop Count
88:Z=X*F (P37)
1:36--X Loc [ co2mVcorr ]
2:-1F
3:36--Z Loc [ co2mVcorr ]
89:End (P95)
90:Else (P94)
4-20
91:End (P95)
92:End (P95)
;Set all the control ports low,
;with a delay.
93:Beginning of Subroutine (P85)
1:9Subroutine 9
94:Excitation with Delay (P22)
1:3Ex Chan
2:0Delay w/Ex (units = 0.01 sec)
3:2Delay After Ex (units = 0.01 sec)
4:0mV Excitation
95:Set Port(s) (P20)
1:9900C8..C5 = nc/nc/low/low
2:0000C4..C1 = low/low/low/low
96:End (P95)
End Program
SECTION 4. SAMPLE 023/CO2 PROGRAM
TABLE 4.2-2. Output From Example 023/CO2 Bowen ratio System Program
01: 21 Array ID, 20 minute gradient data
02: Year
03: Day
04: hhmm
05: CO2mVcorr
06: H2OmVcorr
07: CO2 corr
08: H2O corr
09: T Anlyzr
10: CO2 ref uM
11: H2O ref mM
12: P kPa
13: Vr CO2 mV
14: Vr H2O mV
15: G CO2
16: G H2O
17: TC lower
18: del TC
19: RefTemp
20: Ta/To CO2 during SCRUB
21: Ta/To H2O during SCRUB
01: 22 Array ID, 20 minute energy balance and meteorological data
02: Year
03: Day
04: hhmm
05: T amb C
06: e amb kPA
4-21
SECTION 4. SAMPLE 023/CO2 PROGRAM
07: H2O mM/M
08: Rn
09: SHF#1
10: SHF#2
11: avg Tsoil
12: del Tsoil
13: RH frac
14: Batt Volt
15: Wind Spd
16: Wind Dir
17: Std Wind Dir
18: CS615 mSec
19: Soil Water
20: Soil Water Corr. for Temp.
4-22
SECTION 5. STATION OPERATION
This section assumes that the operator has a fundamental understanding of the CR23X keyboard
commands. Specifically, viewing input locations and setting flags. For information on keyboard
operation, see the overview section of the CR23X manual.
5.1 PUMP
The pump is turned on by setting flag 5 and
then flag 6 high. After the pump has started,
set flag 5 low. To turn the pump off, set flag 5
high and flag 6 low. When the pump turns off,
set flag 5 low.
NOTE: When flag 5 is high no averaging
takes place on the water vapor or carbon
dioxide data. When flag 5 is set low
averaging resumes on the next four minute
cycle.
5.2 MANUAL VALVE CONTROL
Set flag 5 high to active manual valve control.
Flag 2 is used to switch the inputs on the
LI-6262. When flag 2 is high the upper arm is
routed to the sample input and the lower arm to
the reference input. The opposite is true when
flag 2 is low. To exit manual valve control set
flag 5 low.
NOTE:
takes place on the water vapor or carbon
dioxide data. When flag 5 is set low
averaging resumes on the next four minute
cycle.
When flag 5 is high no averaging
5.3 ZERO AND SPAN CALIBRATION
Before the zero and span calibration can be
performed, the 023/CO2 system must go
through at least one scrub cycle. An automatic
scrub is performed at the top of the hour. A
manual scrub is performed by setting flag 8 high
and then low. The manual scrub takes one
minute to complete.
5.3.1 ZERO
The zero valve, located on the left side of the
black mounting bracket, is used to route the air
stream from a single level into both the
reference and sample inputs of the LI-6262.
Flag 2 determines which level is being split.
When flag 2 is high the air is from the lower
arm. When flag 2 is low the air is from the
upper arm. The air stream is split when the
zero switch is in the forward position.
CAUTION:
the operate (backward) position after zero
calibration of the LI-6262.
Set flag 5 high (disable averaging) and flag 2
low. Move the zero switch to the zero (forward)
position. Display the carbon dioxide gradient on
the CR23X (Input Location 30). Unlock the
carbon dioxide zero potentiometer and adjust it
until the gradient is close to zero. Lock the
carbon dioxide zero potentiometer.
Display the water vapor gradient on the CR23X
(Input Location 31). Unlock the water vapor zero
potentiometer and adjust it until the gradient is
close to zero. Lock the zero potentiometer and
move the zero switch into the operate (backward)
position. Set flag 5 low.
Wait four minutes or until flag 1 goes low before
continuing to the span calibration. For more
information on the zero calibration see Section
4.2 of the LI-6262 manual.
5.3.2 SPAN
Set flag 8 (Manual Scrub) high. After the valves
latch, set flag 5 high and wait one minute for the
carbon dioxide and water vapor to be scrubbed
from the LI-6262 sample cell. Check the water
vapor concentration in Input Location 3
(HMP45C) and make a mental note of that
value. Display the absolute water vapor
concentration measured by the IRGA on the
CR23X (Input Location 29). Unlock the water
vapor span potentiometer and adjust it until the
absolute concentration is close to that of the
HMP45C (Input Location 3). Note that the
CR23X does not correct the absolute water
vapor concentration for T/To. This correction is
applied in the SPLIT parameter file
RAWBRC.PAR.
Set flag 6 low (turn pump off). Plumb a carbon
dioxide span gas, through a "T" connector, that
is vented to the atmosphere, and an ACRO50
Be sure to place the switch in
5-1
SECTION 5. STATION OPERATION
filter into the upper arm input on the first valve
(see Figure 5.3-1). Open the span gas bottle so
that there is a slight flow venting out through the
"T" connector into the atmosphere. Set flag 6
high (turn pump on). Display the absolute
carbon dioxide concentration on the CR23X
(Input Location 28). Unlock the carbon dioxide
span potentiometer and adjust it until the
absolute concentration is close to the span gas
concentration in µmol/mol. Note that the
CR23X does not correct the absolute carbon
dioxide concentration for T/To. This correction
is applied in the SPLIT parameter file
RAWBRC.PAR. Set flag 6 low (turn pump off).
Plumb the upper arm back into the valve. Set
flag 6 high (turn pump on).
Lock the span potentiometers and set flag 8 and
5 low. For more information on the span
calibration see Section 4.2 of the LI-6262 manual.
NOTE: There will be small zero offset with
the water vapor span calibration, therefore,
repeat the water vapor zero calibration.
CAUTION: Do not leave flag 8 high
(manual scrub mode) for prolonged periods
of time. Doing so will shorten the useful life
of the soda lime and magnesium
perchlorate and result to contamination of
the LI-6262 sample cell.
5.4 ROUTINE MAINTENANCE
Replace air intake filters*1-2 weeks
Clean thermocouplesas needed
Clean Radiometer domesas needed
Replace Soda Lime and
Magnesium Perchlorateas needed
*Gelman ACRO50 inline Teflon filters with a
1 µm pore size
To disable averaging while replacing filters and
cleaning thermocouples set flag 5 high. Set flag 5
low when maintenance is complete. Averaging will
resume on the next four minute cycle.
Before removing the filters, turn the pump off
(see Section 5.1). Install the clean filters with
the printed side down. Remove all debris from
the fine wire thermocouples. A camel-hair
brush and tweezers can be used to clean the
thermocouples.
The thermocouples can also be dipped in a mild
acid to dissolve spider webs. For example,
muriatic acid (hydrochloric acid) is available in
most hardware stores. Rinse the thermocouples
thoroughly with distilled water after dipping.
For the meteorological sensors, follow the
recommended maintenance in the operator’s
manual and the weather station installation manual.
5-2
To Span
Gas
“T” Connector
Valve A
Upper
Arm
Input
Printed
Side of
ACRO 50
FIGURE 5.3-1. Assembly for Spanning the LI6262
Lower
Arm
Input
ACRO 50
Filter
SECTION 6. CALCULATING FLUXES USING SPLIT
SPLIT (PC208W software) can be used to calculate fluxes from the data produced by the 023/CO2
Bowen Ratio System with CO2 Flux. This section describes those calculations.
Two runs are required using SPLIT to compute the fluxes. The first run operates on the raw data files
generated by the CR23X. The definitions of the points in this data set are given in Table 5. The output
file from the first run (RAWBRC.PRN) is defined in the parameter file RAWBRC.PAR in Table 6. The
fluxes and corrections are then calculated during the second run using SPLIT with the parameter file
CALCBRC.PAR.
The example SPLIT parameter files are available on the Campbell Scientific ftp site,
ftp://ftp.campbellsci.com/pub/outgoing/files/br_co2.exe. Br_co2.exe is a self extracting file. Type
br_co2.exe at a DOS prompt and press the <Enter> key.
6.1 WEBB ET AL. CORRECTION
When carbon dioxide gradients are measured
insitu using the mean gradient technique and
are brought to a common analyzer temperature
and pressure. It is necessary to account for
carbon dioxide density changes caused by the
simultaneous flux of heat and/or water vapor
(Webb et al., 1980).
Start with Webb et al.’s Eq. (36)
∆ρ
PT
=+
Fk
cc
where F
is the total atmospheric pressure, P
pressure within the LI-6262, T is the ambient air
temperature, T
6262,
the density of dry air, and
water vapor where the subscript i indicates that
the densities are at the pressure and
temperature of the LI-6262, k
diffusivity for carbon dioxide, M
molecular weights of dry air and water vapor
respectively, and z is height.
The first term on the right hand side is the
carbon dioxide flux and the second term is the
Webb et al. correction. The datalogger outputs
the gradient of carbon dioxide and water vapor
as a concentration and not a density. Thus, it
would be convenient to write Eq. (22) in terms
of a concentration.
Start with the ideal gas law
PVnRT=(23)
iici
∆
PTz
is the flux density of carbon dioxide, P
c
is the temperature within the LI-
i
is the density of carbon dioxide,
ρ
ci
k
c
PTPTM
iiaci
Mz
ρ
∆ρ
ρ
vi
∆
ρ
vai
is the
i
is the density of
vi
is the eddy
c
and Mv are the
a
ρ
(22)
is
ai
where V is the volume, n is the number of
moles of the gasses in the volume, and R is the
universal gas constant.
= na/V, Nv = nv/V, and Nc = nc/V where
Let N
a
the subscripts a, v, and c are dry air, water
vapor, and carbon dioxide and N is the number
of moles per unit volume of dry air, water vapor,
and carbon dioxide. The ideal gas law can now
be written in the following form.
P
RNNN
=++(24)
()
T
Note that N
partial pressure contribution of carbon dioxide
can be absolved and Eq. (24) assumes the form
below.
P
T
Substituting Eq. (25) into (22) yields the
following.
F
By definition
Mci. It then follows that:
FM
avc
<< Na and Nc << Nv. Thus, the
c
i
=+(25)
RNN
()
i
c
cc
aivi
NN
()
[]
k
P
c
=
T
=
ciaivi
R
k
+
T
k
P
c
R
T
∆
M
P
ca
R
M
vciai
= Nai Mai,
ρ
ai
NNN
[]
ciaivi
+∆ρ
z
∆ρ
[]
ρ
ρ
()
∆
+∆
z
ρ
vi
viaivi
+
NN
()
∆
z
= Nvi Mvi,
= N
ρ
ci
(26)
ci
6-1
SECTION 6. CALCULATING FLUXES USING SPLIT
k
cci
+
M
c
T
[]
P
N
R
N
ai
∆
NN N
+
viaivi
∆
z
is true and finally,
∆
PMTRc
Fk
=+
cc
c
∆
k
c
z
PMTRcww
c
∆
.(28)
−
∆
1
z
The flux of carbon dioxide is now written in
terms of a concentration gradient. Similarly, the
flux of water vapor can be written as follows:
∆
PMTRw
=+
λλ
Lk
ev
v
∆
z
PMTRwww
k
v
v
∆
.(29)
−
∆
1
z
6.2 SOIL HEAT FLUX AND STORAGE
The soil heat flux at the surface is calculated by
adding the measured flux at a fixed depth, d, to
the energy stored in the layer above the heat
flux plates. The specific heat of the soil and the
change in soil temperature, ∆T
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:
=+ =+ρθ ρθρ
CCCC C
()
sbdmw bdvww
, over the output
s
(27)
(30)
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. (32).
∆
TCd
ss
=
S
t
6.3 COMBINING RAW DATA
First, the air temperature, and water vapor and
carbon dioxide concentration gradients must
combined into one file with net radiation, soil
heat flux, and change in soil temperature. To
do this use the SPLIT parameter file called
RAWBRC.PAR. This parameter file assumes
that the data files from the datalogger were
saved on disk under the name BRC.DAT. It
creates a file with the raw data necessary to
calculate fluxes (RAWBRC.PRN).
Plot the data in RAWBRC.PRN, check the
temperature, water vapor, and carbon dioxide
gradients as well as the soil heat flux, soil
temperature, delta soil temperature, and net
radiation for anomalous readings. Check the
wind speed and direction to determine if the
fetch conditions are adequate.
Plot the battery voltage as well. A steady
decrease in the battery voltage and then sudden
increase could indicate the LI-6262 has shut
down.
(32)
ρ
θ
where C
bulk density,
heat capacity of a dry mineral soil,
water content on a mass basis,
content on a volume basis, and C
w
θ
=
m
v
ρ
b
is the heat capacity of moist soil,
S
is the density of water, Cd is the
ρ
w
is soil water
θ
v
w
θ
m
is the heat
is soil
(31)
ρ
b
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 water
content reflectometer. The value used for the
6-2
is
6.4 CALCULATING FLUXES
Once the necessary data is in one file, the
fluxes can be calculated using the example
SPLIT parameter file CALCBRC.PAR. The
SPLIT parameter file CALCBRC.PAR assumes
that the Bowen ratio arms are installed with a
1.0 meter separation (DZ=1.). If your arms are
installed with different separation, change DZ
accordingly. CALCBRC.PAR assumes that the
volumetric soil water content was measured by
a CS615. If the soil water content was
determined by other means, the parameter file
must be changed accordingly. The constants
and parameters necessary for calculating the
fluxes are listed in Table 6.4-1. All of the
calculations in CALCBOW.PAR are explained in
Sections 1, 6.1, and 6.2. Unit analysis for
selected sections of CALCBRC.PAR is given in
Table 6.4-2.
SECTION 6. CALCULATING FLUXES USING SPLIT
TABLE 6.4-1. Input Values for Flux Calculations
VARVALUEUNITSDESCRIPTION
44.0g mol
8.314Jkg
-1
-1
mol
-1
Universal gas constant
Molecular weight of carbon dioxide
0.622Molecular weight of water divided by weight of air
BBowen Ratio
DB*1200.0kg/m
3
Soil bulk density (must be measured for the site)
CPkJ/(kg K)Specific heat of moist air
1.005kJ/(kg K)Specific heat of dry air
840.0J/(kg
4190.0J/(kg
DZ1.0mArm separation (z
K)Specific heat of dry soil
K)Specific heat of water
- z2)
1
0.08**mDepth of soil heat flux plates
EWkJ/kgLatent heat of vaporization
2450.0kJ/kgLatent heat of vaporization at 20
FW/m
FCmg/(m
GW/m
HW/m
Km
2
2
s)Carbon dioxide flux
2
2
2
/sEddy diffusivity for carbon dioxide (assumed to
Soil heat flux measured at 8 cm
Soil heat flux at surface (F+S)
Sensible heat flux
equal to the eddy diffusivity for heat and water vapor)
O/bulk vol-soil Soil Water Content on a volume basis measured by the
2
CS615
2
WPLCmg/(m
WPLVW/m
s)Webb et al. correction for carbon dioxide flux
2
Webb et al. correction for latent heat flux
o
C
* These values are unique for a site. Correct values must be entered for the site under study.
** These values may need to change if the program or installation differs from the example.
6-3
SECTION 6. CALCULATING FLUXES USING SPLIT
TABLE 6.4-2. Selected Code from CALCBRC.PAR with Unit Analysis
SPLIT Code
Equation
Q=(.622*13)/(8-(13*.378))
ε
=
q
CP=(1.+(.87*Q))*1.005
e
()
−−
Pe
1
ε
Units
kPa
[]
unit less
[]
=
kPa
[]
()
=+
1087.
CqC
()
ppdry
RD=(8-13)*1000./(287.05*(12+273.15))
()
−
Pe
ρ
=
d
RT
RV=13*1000./(461.5*(12+273.15))
ρ
=
v
RT
EW=2500.5-2.359*12
λλ=−
B=CP*10*1000./(.622*EW*5)
CT T
p2 1
β
=
ελ
1000
()
+
27315.
d
e
1000
()
+
27315.
v
o
()
ww
()
T2359.
−
1000
−
21
-1-1
kJ K
[]
-3
kg m
[]
kg m
[]
[]
unit less
=
-3
=
kJ K kgKmmol mol
[]
=
kg
[]
1000
kPaPa kPa
[]
-1-1
kg
J KK
[]
[]
1000
kPaPa kPa
[]
-1-1
kg
J KK
[]
-1
kJ kg
[]
-1 -1
[]
1000
[]
-1-1
kJ kgmmol mol
[][]
[]
[]
S=19*.08*(DB*840.+W*1000.*4190.)/1200.
Td CC
sddvww
=
S
K=DZ*H/(10*CP*1000.*RA)
=
k
c
TTC
()
21
FC=K*8*44.*4/((12+273.15)*8.314*DZ)
6-4
+∆ρ θρ
()
t
−
zzH
()
12
−
ρ
1000
pa
[][]
Kmkg m J kgK
-2
W m
[]
2
-1
ms
[]
=
=
[]
K kJ kg KJ kJ kg m
-1 -1-
[]
-3-1 -1
[][]
[]
s
[]
mWm
-2
[]
1000
[]
3
[]
−
P M
kcc
()
21
cc
=
F
c
T R z
WPLV=LE*7/(1000.-7)
−
()
12
SECTION 6. CALCULATING FLUXES USING SPLIT
21
--1-1
[]
m skPamol molg mol
-2 -1
mg m
z
[]
[]
=
s
µ
[][]
[]
-1-1
J K mol
Km
[]
[]
Lw
e
WPLV
WPLC=K*8*44.*6*5/((12+273.15)*8.314*DZ*(1000.-7))
WPLC
=
P M c
Kww
cc
=
T R zzw
()
−
1000
12
w
−
()
21
()
−−
1000
-2
W m
[]
m skPa g molmol molmmol mol
-2 -1
mg m s
[]
[]
=
[]
K J K molmmmol mol mmol mol
[]
-2-1
Wmmmol mol
=
2
[][]
m m ol molmmol mol
1000
[]
-1-1-1-1
[]
[][][]
-1-1-1
[]
−
[]
µ
1000
[]
-1
−
6-5
APPENDIX A. REFERENCES
Bowen, I. S., 1926: The ratio of heat losses by
conduction and by evaporation from any
water surface.
Brutsaert, W., 1982:
Atmosphere.
pp.
Dyer, A. J., and W. O. Pruitt, 1962: Eddy flux
measurements over a small irrigated area.
J. Appl. Meteor.,
Gash, J. H. C., 1986: A note on estimating the
effect of a limited fetch on micrometeorological evaporation measurements.
Phys. Rev.
Evaporation into the
D. Reidel Publishing Co., 300
1, 471-473.
Bound.-Layer Meteor.,
Hanks, R. J., and G. L. Ashcroft, 1980:
, 27, 779-787.
35, 409-413.
Applied
Soil Physics: Soil Water and Temperature
Application.
Klute, A., 1986:
Part 1, Sections 13 and 21, American
Society of Agronomy, Inc., Soil Science
Society of America, Inc.
Lemon, E. R., 1960: Photosynthesis under field
conditions: II. An aerodynamic method for
determining the turbulent carbon dioxide
exchange between the atmosphere and a
corn field.
Lowe, P. R., 1976: An approximating
polynomial for computation of saturation
vapor pressure.
103.
Springer-Verlag, 159 pp.
Method of Soil Analysis.
Agron. J.
, 52, 697-703.
J. Appl. Meteor.
, 16, 100-
No. 9,
Ohmura, A., 1982: Objective criteria for
rejecting data for bowen ratio flux
calculations.
Schuepp, P. H., M. Y. Leclerc, J. I.
MacPherson, and R. L. Desjardins, 1990:
Footprint prediction of scalar fluxes from
analytical solutions of the diffusion
equation.
373.
Shuttleworth, W. J., 1992: Evaporation
(Chapter 4),
Maidment, Ed., Mc Graw-Hill, 4.1-4.53.
Tanner, C. B., 1960: Energy balance in
approach to evapotranspiration from crops,
J. Appl. Meteor.
Bound.-Layer Meteor.,
Handbook of Hydrology,
Soil Sci. Soc. Am. Proc.,
Tanner, C. B., 1979: Temperature: Critique I.
, 21, 595-598.
50, 355-
24, 1-9.
Controlled Environmental Guidelines for
Plant Research
Kozolowski, Eds., Academic Press, 117-
130.
Wallace, J. M., and P. V. Hobbes, 1977:
, T. W. Tibbits and T. T.
Atmospheric Science: An Introductory
Survey.
Webb, E.K., G. I. Pearman, and R. Leuning,
1980: Correction of flux measurement for
density effect due to heat and water vapour
transfer.
85-100.
Academic Press, 350 pp.
Quart. J. Roy. Meteor. Soc
., 106,
A-1
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