Campbell Open Path Eddy Covariance System User manual

Open Path Eddy Covariance System
Operator’s Manua
l
CSAT3, LI-7500, and KH20
9/06
Copyright © 2004-2006
Campbell Scientific, Inc.

Warranty and Assistance
The OPEN PATH EDDY COVARIANCE (OPEC) SYTEM is warranted
by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and
workmanship under normal use and service for twelve (12) months from date
of shipment unless specified otherwise. Batteries have no warranty.
CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to
repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective
products. The customer shall assume all costs of removing, reinstalling, and
shipping defective products to CAMPBELL SCIENTIFIC, INC. CAMPBELL
SCIENTIFIC, INC. will return such products by surface carrier prepaid. This
warranty shall not apply to any CAMPBELL SCIENTIFIC, INC. products
which have been subjected to modification, misuse, neglect, accidents of
nature, or shipping damage. This warranty is in lieu of all other warranties,
expressed or implied, including warranties of merchantability or fitness for a
particular purpose. CAMPBELL SCIENTIFIC, INC. is not liable for special,
indirect, incidental, or consequential damages.
Products may not be returned without prior authorization. The following
contact information is for US and International customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit
www.campbellsci.com to determine which Campbell Scientific company
serves your country. To obtain a Returned Materials Authorization (RMA),
contact CAMPBELL SCIENTIFIC, INC., phone [phone]. After an
applications engineer determines the nature of the problem, an RMA number
will be issued. Please write this number clearly on the outside of the shipping
container. CAMPBELL SCIENTIFIC's shipping address is:
CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784
CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

i
Open Path Eddy Covariance System
Table of Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. System Description .....................................................1
1.1 OPEC (CSAT3 Only) ...............................................................................1
1.2 Basic OPEC ..............................................................................................1
1.3 Extended OPEC........................................................................................1
1.4 Additional Fast Response Sensors............................................................2
2. Installation and Mounting ...........................................2
2.1 Fetch and Sensor Height...........................................................................3
2.2 Mounting ..................................................................................................4
2.2.1 Measure CSAT3 Azimuth...............................................................9
2.3 Wiring.......................................................................................................9
2.4 Power........................................................................................................9
3. System Datalogger Program ....................................10
3.1 Generic Program Flowchart....................................................................12
3.2 Program Configuration ...........................................................................13
3.2.1 CSAT3 Azimuth ...........................................................................14
3.2.2 Sensor Configuration ....................................................................15
3.3 Loading a Program to the Datalogger.....................................................16
3.3.1 Direct Connection via LoggerNet .................................................16
3.3.2 Remote via PC/CF Card................................................................16
3.4 System Operation....................................................................................17
3.4.1 Monitoring Data............................................................................17
3.4.2 Status Table...................................................................................18
4. Data.............................................................................18
4.1 Data Retrieval .........................................................................................19
4.1.1 Direct Connection Data Retrieval via LoggerNet.........................20
4.1.2 File Management with Baler.........................................................23
4.1.3 Remote Data Retrieval via a PC/CF Card.....................................24
4.1.4 File Management with CardConvert.............................................25
4.1.4.1 Collecting Data with One Card ...........................................29
4.1.4.2 Collecting Data with Two Cards .........................................30
4.2 Data Processing ......................................................................................31
4.2.1 Online Processing .........................................................................32
4.2.2 Off-line Processing with EdiRe ....................................................32
4.2.2.1 Creating Raw File Format and Processing Lists..................33
4.2.2.2 Example EdiRe Raw File Format and Processing Lists ......35
5. Eddy Covariance Theory 101....................................39

Open Path Eddy Covariance System Table of Contents
ii
A. CSAT3 Orientation .................................................. A-1
A.1 Determining True North and Sensor Orientation................................ A-1
A.2 Online Magnetic Declination Calculator............................................. A-3
B. Sensible Heat Flux without a FW05 ....................... B-1
B.1 Speed of Sound and Sonic Temperature ............................................. B-1
B.2 Sonic Temperature, Temperature, and Humidity ................................ B-2
B.3 Sensible Heat and Specific Humidity Flux ......................................... B-3
B.4 Sensible and Latent Heat Flux............................................................. B-4
Appendix C. References..............................................C-1
Figures
1. Eddy Covariance Sensors Mounted on a CM10 Tripod ............................ 3
2. Side View of the CSAT3 and LI-7500 (mounted underneath CSAT3) ..... 5
3. Side View of the CSAT3 and LI-7500 (mounted beside CSAT3)............. 5
4. CM110 Enclosure Mounting Hardware Attached to the LI-7500
Electronics Box .......................................................................................... 6
5. Close Up View p/n 17716, configured for ENC 10/12, Locking
Mechanism ................................................................................................. 6
6. CSAT3 Electronics Box and p/n 17813 Enclosure Hanger Kit on
CM110 Tripod Body .................................................................................. 7
7. CSAT3 and LI-7500 Electronics Boxes Mounted on the CM110
Tripod Body ............................................................................................... 7
8. ENC12/14 Enclosure Mounted on the CM110 Tripod Base ..................... 8
9. HMP45C 10-plate Radiation Shield Mounted on the Body of the
CM110 and on the CM204 Horizontal Crossarm....................................... 8
10. Terminal Strip Adapters for Power Connection to External Battery ..... 10
11. CSAT3 Right Hand Coordinate System, Horizontal Wind Vector
Angle is 0 Degrees.................................................................................... 14
12. Compass Coordinate System, Compass Wind Direction is 140
Degrees..................................................................................................... 15
13. LoggerNet Station Setup for the “flux” table......................................... 21
14. LoggerNet Station Setup for the “ts_data” Table .................................. 21
15. LoggerNet Station Data Collection Schedule ........................................ 22
16. LoggerNet Station Status Monitor ......................................................... 22
17. Baler Station Setup for the “flux” Table................................................ 23
18. Baler Station Setup for the “ts_data” Table ........................................... 24
19. File Format Flow.................................................................................... 26
20. Destination File Option Screen .............................................................. 27
21. Fully Configured CardConvert Start Up Screen .................................... 28
22. List of Files Created by CardConvert .................................................... 28
23. List of Files Created by CardConvert with Duplicates .......................... 29
24. List of Files Where the Duplicate Files are Renamed to *.bak.............. 30
25. List of Files Collected the First Time Using Two Cards ....................... 31
26. List of Files Collected the Second time Using Two Cards .................... 31
27. Interpreter Settings to Read a Campbell Scientific, Inc. TOB1
Data File ................................................................................................... 34
28. Folder that Contains the Raw TOB1 Time Series Data Files................. 34
29. Competed Interpreter Screen ................................................................. 35
30. Estimated Sample Frequency and Correct Sample Frequency .............. 35

Open Path Eddy Covariance System Table of Contents
iii
31. Default EdiRe Processing List Created by the Interpreter......................36
32. Output File Location as Part of the Processing List ...............................37
33. Output File Location as Part of the Processing List ...............................37
34. Processing Uzand CO2with 1 Chn Statistics Instruction........................38
35. Computing CO2Flux with 2 Chn Statistics and Graphing UzStatistic
with Plot Value Instruction .......................................................................38
36. Ideal Vertical Profiles of Virtual Potential Temperature and Specific
Humidity Depicting All the Layers o the Atmospheric Boundary Layer..39
A-1. Magnetic Declination for the Conterminous United States (2004) ... A-1
A-2. A Declination Angle East of True North (Positive) is Subtracted
from 360 (0) degrees to Find True North............................................... A-2
A-3. A Declination Angle West of True North (Negative) is Subtracted
from 0( 360) degrees to Find True North............................................... A-2
A-4. Online Magnetic Declination Calculator with Inputs and Output
for Longmont, CO.................................................................................. A-3
Tables
1. Nominal Sensor Power Requirements ........................................................9
2. Nominal Datalogger Power Requirements with the Display Off and
No RS-232 Communications ......................................................................9
3. Nominal Datalogger Power Requirements with the Display and
Backlight On, and No RS-232 Communications ........................................9

Open Path Eddy Covariance System Table of Contents
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1
Open Path Eddy Covariance System
This document will serve as a guide to properly install and operate a Campbell Scientific,
Inc. Open Path Eddy Covariance System (OPEC). The OPEC is composed of various
products, e.g. dataloggers, fast response turbulence sensors, slow response meteorological
sensors, and software. These products are manufactured by Campbell Scientific, Inc. and
other vendors. Manuals for each of these sensors shipped with the system. It is time well
spent reviewing these documents.
The literature contains information that spans 50 years on eddy covariance (correlation)
theory and measurements. Section 5ever so briefly touches eddy covariance theory. For
more details on eddy covariance measurements and data analysis, see the literature.
1. System Description
The Campbell Scientific, Inc. eddy covariance systems measure sonic sensible
heat flux, momentum flux, and the flux of other scalars between the
atmosphere and earth’s surface. The system consists of a datalogger, fast
response three-dimensional sonic anemometer, and fast response scalar
sensors. An independent measure of temperature and humidity from a slow
response sensor is also measured to calculate background meteorological
variables. Horizontal wind speed and direction are computed by the datalogger
from the three-dimensional measurements of wind made by the sonic
anemometer.
1.1 OPEC (CSAT3 Only)
The minimum components required for eddy covariance measurements are a
datalogger, a CSAT3 three-dimensional sonic anemometer, and a HMP45C
temperature and humidity probe. This system configuration measures sonic
sensible heat flux, momentum flux, temperature, humidity, horizontal wind
speed, and wind direction. This system configuration is used to compute eddy
diffusivity required to compute fluxes of trace gases measured with a gradient
system like the TGA100A (Warland, et al., 2001).
1.2 Basic OPEC
A more typical eddy covariance system consists of a datalogger, a CSAT3
three-dimensional sonic anemometer, a LI-7500 open path infrared gas
analyzer (IRGA), and a HMP45C temperature and humidity probe. With this
configuration, the system can measure carbon dioxide flux, latent heat flux,
sonic sensible heat flux, momentum flux, a computed sensible heat flux (see
Appendix B), temperature, humidity, horizontal wind speed, and wind
direction.
1.3 Extended OPEC
Energy balance sensors can be added to a basic OPEC system to also measure
the net radiation, soil heat flux, soil temperature, and soil water content. The
sensors required for these additional measurements are a Q7.1, NR-LITE, or
CNR1 net radiometer, two to four HFT3 or SHF01-SC soil heat flux plates,

Open Path Eddy Covariance System
2
one or two TCAV averaging soil temperature probes, and one or two CS616
soil moisture reflectometers.
1.4 Additional Fast Response Sensors
If the application requires a direct measurement of sensible heat flux, a FW05
can be added to the system. In the absence of a FW05 or if the FW05 breaks,
the sensible heat flux can be found from the sonic sensible heat flux and the
latent heat flux (see Equation 36 in Appendix B).
A KH20 Krypton hygrometer, instead of the LI-7500, can be used to measure
the latent heat flux. The KH20 can not be used to measure an absolute
concentration of water vapor, because of scaling on the source tube windows
caused by disassociation of atmospheric continuants by the ultra violet photons
(Campbell and Tanner, 1985 and Buck, 1976). The rate of scaling is a function
of the atmospheric humidity. In high humidity environments, scaling can
occur within a few hours. That scaling attenuates the signal and can cause
shifts in the calibration curve. However, the scaling over a typical flux
averaging period is small. Thus, water vapor fluctuation measurements can
still be made with the hygrometer. The effects of the scaling can be easily
reversed by wiping the windows with a moist swab.
To measure other trace gases, a TGA100A Trace Gas Analyzer can be added to
the system. The TGA100A can measure methane, carbon dioxide isotope,
water vapor isotope, ammonia, and nitrous oxide flux.
2. Installation and Mounting
When making eddy covariance measurements near the surface (less than 3
meters), mount the datalogger enclosure between the legs of the CM11x tripod,
on a separate tripod, or user-supplied drive stake. Also, mount any sensor
electronics boxes as far from the fast response sensors as possible and always
use the tripod guy kit. This will minimize potential flow distortions and tower
sway caused by wind blowing against the fiberglass enclosure. See the tripod
manuals for detailed installation instructions.
Figure 1 depicts a typical eddy covariance station. Point the eddy covariance
sensors into the prevailing wind to minimize the flow distortion from the
tower, mounting hardware, and other sensors.
Keep a log book for each station. Record the date and personnel
name for all site visits, as well as all maintenance and work that
is performed during the site visit.
TIP

Open Path Eddy Covariance System
3
FIGURE 1. Eddy Covariance Sensors Mounted on a CM10 Tripod;
the Datalogger Enclosure is on a Separate Tripod (not pictured)
2.1 Fetch and Sensor Height
The eddy covariance sensors must be mounted at some height to ensure that the
measurements are made within the local surface layer. The local surface layer
grows at a rate of approximately 1 vertical meter per 100 horizontal meters.
Thus, a height to fetch (horizontal distance traveled) ratio of 1:100 may be used
as an absolute bare minimum rough rule of thumb for determining the
measurement height. The following references discuss fetch requirements in
detail: Brutsaert (1982); Dyer and Pruitt (1962); Gash (1986); Schuepp, et al.
(1990); and Shuttleworth (1992).
The fetch should be homogenous and flat, and no abrupt changes in vegetation
height should exist (Tanner, 1988). Consider two adjacent fields, the first
planted with 1 m tall corn and the second with 0.5 m soybean. Eddy
covariance sensors mounted at 2 m above the corn field should have a
minimum of 200 m of fetch in all the directions that the data is of interest,

Open Path Eddy Covariance System
4
particularly between the eddy covariance sensors and the interface between the
corn and soybean field.
2.2 Mounting
The CSAT3, LI-7500, and HMP45C are mounted to a tripod or tower using a
horizontal mounting arm, several Nu-Rail crossover fittings, and short lengths
of pipe.
The CSAT3 is attached to the CM204 (OPEC standard), CM206, or CM208
horizontal mounting arm by a 0.75 inch by 0.75 inch crossover Nu-Rail (p/n
1017), a 1.0 inch by 0.75 inch crossover Nu-Rail (p/n 1049), and a 30.48 cm
(12 inch) length of 0.75 inch diameter pipe (p/n 18048) (Figures 2 and 3).
The LI-7500 can be mounted two ways, underneath the CSAT3 (Figure 2) or
slightly behind the CSAT3 measurement volume (Figure 3) with a separation
of about 15 to 20 cm. The IRGA should be set back from the anemometer to
minimize flow distortions. Tilt the IRGA sensor head about 60 degrees from
horizontal to minimize the amount of precipitation that accumulates on the
windows.
The LI-7500 is attached to the CM204 horizontal mounting arm by a 1.0 inch
by 0.75 inch crossover NU-Rail (p/n 1049), and the Head Mounting Kit
(LI-COR p/n 9975-010), or a 1.0 inch by 0.75 inch crossover NU-Rail
(p/n 1049), a 0.75 inch by 0.75 inch crossover Nu-Rail (p/n1017), a 25.4 cm
(10 inch) length of 0.75 inch diameter pipe (p/n 6332), and the Head Mounting
Kit (LI-COR p/n 9975-010) (Figure 2 and Figure 3).
Attach the enclosure mounting hardware, p/n 17716, to the LI-7500 electronics
enclosure (Figures 4 and 5). Mount the enclosure hanger kit, p/n 17813, and
the CSAT3 electronics as shown in Figures 6 and 7. Finally, mount the
ENC12/14 enclosure on the tripod base as shown in Figure 8.
Mount the HMP45C radiation shield at the same height as the fast response
sensors. The HMP45C radiation shield is mounted to the either the tripod body
or the end of the horizontal cross arm (Figure 9).

Open Path Eddy Covariance System
5
FIGURE 2. Side View of the CSAT3 and LI-7500 (mounted underneath CSAT3)
FIGURE 3. Side View of the CSAT3 and LI-7500 (mounted beside CSAT3)
CM204 Crossarm with
bracket, 1.3 m (4 ft)
p/n 18048 0.75 inch diameter by 30.48
cm (12 inch) long aluminium pipe
p/n 6332 0.75 inch diameter by 25.4
cm (10 inch) long aluminium pipe
p/n 1049 1.0 inch by 0.75 inch
crossover Nu-Rail fitting
p/n 1017 0.75 inch by 0.75 inch
crossover Nu-Rail fitting
p/n 1049 1.0 inch by 0.75 inch
crossover Nu-Rail fitting
CM204 Crossarm with
bracket,1.3 m (4 ft)
p/n 1017 0.75 inch by 0.75 inch
crossover Nu-Rail fitting
p/n 18048 0.75 inch diameter by 30.48
cm (12 inch) long aluminium pipe

Open Path Eddy Covariance System
6
FIGURE 4. CM110 Enclosure Mounting Hardware (p/n 17716 configured for ENC 10/12)
Attached to the LI-7500 Electronics Box
FIGURE 5. Close Up View p/n 17716, configured for ENC 10/12, Locking Mechanism

Open Path Eddy Covariance System
7
FIGURE 6. CSAT3 Electronics Box and p/n 17813
Enclosure Hanger Kit on CM110 Tripod Body
FIGURE 7. CSAT3 and LI-7500 Electronics Boxes Mounted on
the CM110 Tripod Body

Open Path Eddy Covariance System
8
FIGURE 8. ENC12/14 Enclosure Mounted on the CM110 Tripod Base
FIGURE 9. HMP45C 10-plate Radiation Shield Mounted on
the Body of the CM110 (left) and on the CM204 Horizontal Crossarm (right)

Open Path Eddy Covariance System
9
2.2.1 Measure CSAT3 Azimuth
To compute the correct compass wind direction, the station operator must enter
the negative x-axis azimuth of the CSAT3 into the datalogger program. If the
CSAT3 is installed such that it points into the prevailing wind, the negative
x-axis is pointing into the prevailing wind. Take a compass azimuth of the
negative x-axis (prevailing wind) and record it into the station log book for
later use.
2.3 Wiring
A Campbell Scientific, Inc. eddy covariance system can take on several
configurations and utilize several different dataloggers. It is impractical to
document the different wiring schemes in this manual. However, do not
despair; each datalogger program (p/n 18442 or 18443) contains a complete
and detailed wiring diagram. See the datalogger program for wiring
instructions.
2.4 Power
The system requires about 1.5 to 14 W continuous power, depending on the
datalogger and sensor configuration. The approximate power requirements of
various key components, for a system running at 10 Hz, are listed in Tables 1,
2, and 3.
TABLE 1. Nominal Sensor Power Requirements
Sensor Power (mW)
CSAT3 67 mA @ 12.5 Vdc
LI-7500 850 mA @ 12.5 Vdc (after warmup)
KH20 10 - 20 mA @ 12.5 Vdc
HMP45C <3.8 mA @ 12.5 Vdc
TABLE 2. Nominal Datalogger Power Requirements with
the Display Off and No RS-232 Communications
Datalogger Power (mW)
CR1000 w/ CFM100 & CF card 8 mA @ 12.5 Vdc
CR3000 w/ CFM100 & CF card 39 mA @ 12.5 Vdc
CR5000 w/ PC/CF card 63 mA @ 12.5 Vdc
TABLE 3. Nominal Datalogger Power Requirements with
the Display and Backlight On, and No RS-232 Communications
Datalogger Power (mW)
CR1000 w/ CFM100 & CF card 109 mA @ 12.5 Vdc
CR3000 w/ CFM100 & CF card 75 mA @ 12.5 Vdc
CR5000 w/ PC/CF card 170 mA @ 12.5 Vdc

Open Path Eddy Covariance System
10
The CSAT3 and LI-7500 are powered by an external battery. Typically, so is
the datalogger. If a CR3000/CR5000 is to be powered from a base with a
sealed rechargeable battery, connect the datalogger ground lug to the negative
post of the external battery. Ensure that the rechargeable battery is trickle
charged by a solar panel or mains power.
A user-supplied 70 Ahr deep cycle RV battery (degraded by 30%) will run the
system for approximately two days. The battery will have to be charged by a
trickle charger connected to mains power or solar panels. In some
environments, additional batteries or solar panels may be required (see the
Power Supply Application Note 5-F at http://www.campbellsci.com/
documents/apnotes/pow-sup.pdf and the solar panel manual at
http://www.campbellsci.com/documents/manuals/msx.pdf).
The CSAT3 and LI-7500 power cables are connected directly to the battery
terminals by means of two terminal strips (p/n 4386), one for the positive post
and the other the negative post (Figure 10).
FIGURE 10. Terminal Strip Adapters for Power Connection
to External Battery
Power connections are listed in the programs (p/n 18442 or 18443). Be sure
the datalogger has a good earth ground to protect against primary and
secondary lightning strikes. Campbell Scientific, Inc. recommends that all
dataloggers in the field be earth grounded. All components of the system
(datalogger, sensors, external power supplies, mounts, housing, etc.) must be
referenced to one common earth ground. When long cables are used or a site
has frequent lightning strikes, spark gaps may be required to protect the
datalogger from transient voltages.
3. System Datalogger Program
The eddy covariance datalogger program is the single component that
integrates all of the sensors in an eddy covariance station into a single system.
Part number 18442 is a program for a basic system and p/n 18443 is a program
for an extended system (with energy balance sensors). If your order did not
include either p/n 18442 or 18443 as a line item on the order, contact Campbell
Scientific, Inc. to purchase the appropriate datalogger program for your eddy
covariance system.

Open Path Eddy Covariance System
11
The library of programs covers a variety of sensors and is continuously
growing. If your system has sensors that are not part of any program in the
library, simply add the appropriate measurement and processing instructions to
the program or contact Campbell Scientific, Inc. for assistance. Campbell
Scientific, Inc. charges for custom datalogger programming with a one hour
minimum and one hour resolution; call for current Application Engineering
time rates.
The datalogger programs align the measurements in time from the CSAT3,
LI-7500, KH20, and FW05. The CSAT3 has a fixed two scan delay and
LI-7500s shipped from Campbell Scientific, Inc. are programmed with a fixed
300 milliseconds (297.25 milliseconds) delay. These sensor delays are
removed before the time series data is saved to Final Storage and before they
are used to compute the online fluxes.
Depending on the system configuration, the datalogger programs compute
carbon dioxide flux, latent heat flux, sonic sensible heat flux, sensible heat
flux, momentum flux, and friction velocity, along with all the second moment
covariances, standard deviations, and means. The program will also compute a
sensible heat flux from the sonic sensible heat flux and latent heat flux (see
Appendix B). Each datalogger program is shipped with a Microsoft®Excel
workbook (tab) that describes the datalogger program outputs. There is one
worksheet (tab) per output data table.

Open Path Eddy Covariance System
12
3.1 Generic Program Flowchart
FALSE
FALSE
(disable_flag_on(3) = FALSE)
Enable count of warning flags
(disable_flag_on(3) = TRUE)
Disable count of warning flags
TRUE
Is the CSAT3 warning not a diagnostic code?
FALSE
(disable_flag_on(1) = FALSE)
Enable covariance processing
(disable_flag_on(1) = TRUE)
Disable covariance processing
TRUE
Are any CSAT3 warning flags set?
Convert CSAT3 diagnostic word into seperate warning flags
Convert LI-7500 data from molar density to molar fraction
Convert LI-7500 data from molar density to mass density
Convert CSAT3 data for WindVector (): wind_east = -Uy, wind_north = Ux
- Load the FW05 data from (OFFSET - 0) scans back
- Load the KH20 data from (OFFSET - 0) scans back
- Load the LI-7500 data from (OFFSET - 1) scans back
- Load the CSAT3 data from (OFFSET - 2) scans back
Retrieve buffered data and apply the appropriate lag:
TRUE
>= offset?)
Are enough data buffered to undo sensor lags? (scan_count
- CS616
- TCAV
- HFP01SC/HFT3
- Q7.1/NRLite/CNR1
- battery voltage
- HMP45C
- LI-7500
- CSAT3
- KH20
- FW05
- datalogger panel temperature
Measure Sensors:
Scan every 0.1 or 0.05 seconds
Set default values for all variables:

Open Path Eddy Covariance System
13
FALSE
scan_count+1
scan_count =
Call flux data table
FALSE
- Calculate the oxygen correction
- Calculate a computed sensible heat flux
- Calculate Webb et al. term
- Compute the fluxes from the covariance values
- Calculate the CSAT3 wind direction
- Calculate the compass wind direction
- Load the calculated covariances
Perform online processing:
TRUE
calculated?
Have new covariances been
Call the online covariance calculation data table (comp_cov)
Call time series data table (delay adjusted)
FALSE
save_ts_flag_on = FALSEsave_ts_flag_on = TRUE
TRUE
Is it even minute?
Save the 4 most significant bits of the LI-7500 diagnostic word
FALSE
flags (disable_flag_on(4) = FALSE)
Enable count of LI-7500 warning
TRUE)
(disable_flag_on(4) =
warning flags
Disable count of LI-7500
TRUE
LI-7500 CO2 = NAN or SDM error?
FALSE
(disable_flag_on(2) = FALSE)
Enable covariance processing
TRUE)
(disable_flag_on(2) =
processing
Disable covariance
TRUE
Are any LI-7500 warning flags true?
Convert LI-7500 diagnostic word into seperate warning flags
Compute LI-7500 AGC
Flip the diagnostic bits in the LI-7500 diagnostic
Save the 4 most significant bits of the CSAT3 diagnostic word
TRUE
continuation of scan_count >= offset?
3.2 Program Configuration
The site attendant must enter unique calibration coefficients or site-specific
information into the datalogger program. This information includes, but is not
limited to, the CSAT3 azimuth, calibration coefficients for the net radiometer
and soil heat flux plates, or site pressure. To find the section of the program
where these changes are made, search for the text “Unique value”.

Open Path Eddy Covariance System
14
3.2.1 CSAT3 Azimuth
The example programs report the wind direction in both the CSAT3 coordinate
system (a right-handed coordinate system) and in the compass coordinate
system (a screwball left-handed coordinate system). The CSAT3 coordinate
system is relative to the CSAT3 itself and does not depend on the CSAT3’s
orientation (azimuth of the negative x-axis). The compass coordinate system is
fixed to the earth. In order for the programs to compute the correct compass
wind direction, the azimuth of the CSAT3 negative x-axis must be entered into
the program. The program default value for CSAT3_AZIMUTH is 0. This
assumes that the prevailing wind is from the North, e.g. the CSAT3 is mounted
such that the negative x-axis points to the North.
As described in Section 2 and 2.2.1, orient the CSAT3 so that it is pointing into
the prevailing wind direction. If you have done so, the CSAT3 negative
x-axis will point into the prevailing wind direction. Enter this prevailing wind
direction for the constant CSAT3_AZIMUTH (see the station log book for this
bearing).
Don’t forget to account for the magnetic declination at the site;
see Appendix A for details.
Figures 11 and 12 show the orientation of a CSAT3 with a compass bearing of
140 degrees, e.g. the negative x-axis is pointing into 140 degrees. If the wind
is blowing into the CSAT3, from the negative x-axis to the positive x-axis
(from the transducers to the block), the horizontal wind vector angle
(wind_dir_csat3) is 0 degrees (wind vector) and the compass wind direction
(wnd_dir_compass) is 140 degrees (wind vane).
North
Y
X
Wind Vane
Wind Vector
FIGURE 11. CSAT3 Right Hand Coordinate System,
Horizontal Wind Vector Angle is 0 Degrees
NOTE