BOREAS TF-11 SSA-Fen Tower Flux and Meteorological Data
Summary
The BOREAS TF-11 team collected energy, carbon dioxide, and methane flux data at
the BOREAS SSA-Fen site during the growing seasons of 1994 and 1995
Table of Contents
* 1 Data Set Overview
* 2 Investigators
* 3 Theory of Measurements
* 4 Equipment
* 5 Data Acquisition Methods
* 6 Observations
* 7 Data Description
* 8 Data Organization
* 9 Data Manipulations
* 10 Errors
* 11 Notes
* 12 Application of the Data Set
* 13 Future Modification and Plans
* 14 Software
* 15 Data Access
* 16 Output Products and Availability
* 17 References
* 18 Glossary of Terms
* 19 List of Acronyms
* 20 Document Information
1. Data Set Overview
1.1 Data Set Identification
BOREAS TF-11 SSA-Fen Tower Flux and Meteorological Data
1.2 Data Set Introduction
This data set includes heat, carbon dioxide, and methane fluxes measured by eddy
correlation and meteorological data all measured at the Boreal Ecosystem-
Atmosphere Study (BOREAS) Southern Study Area (SSA)-Fen site.
1.3 Objective/Purpose
This overall project has the following research components:
a) Quantification of surface exchange rates of methane and carbon dioxide
(using the micrometeorological eddy correlation technique) at a boreal
wetland site.
b) Evaluation of soil surface carbon dioxide flux and characterization of its
response to controlling variables (such as temperature, water content, and
water table depth).
c) Experimental quantification of the responses of leaf photosynthesis, plant
respiration, and stomatal conductance of dominant plant species to relevant
controlling variables.
d) Process studies, which include field experimental manipulations to quantify
the degree of substrate of pH limitations of methane production and
oxidation.
1.4 Summary of Parameters
The variables measured include latent heat flux, sensible heat flux, carbon
dioxide flux, methane flux, net radiation, incident Photosynthetic Photon Flux
Density (PPFD), incident and reflected solar radiation, wind speed and
direction, soil temperatures, precipitation amount, air temperature, absolute
humidity, vapor pressure deficit, air pressure, and water table height.
1.5 Discussion
In BOREAS, each surface flux site was located in a unique boreal forest
ecosystem component in northern and southern study areas, in an attempt to
characterize the boreal forest at both the northern and southern extremes of its
extent. In this study, the surface flux station was deployed in a wetland
environment of the SSA to make measurements of the fluxes of carbon dioxide,
methane, and the energy budget components. These fluxes were considered
important in characterizing wetlands of the boreal forest. The surface fluxes
were measured using the eddy correlation technique. Supporting meteorological
measurements were also made at this site.
A pilot study was conducted during August-September of 1993. A more extensive
study was conducted from May to October in 1994 and in 1995.
1.6 Related Data Sets
BOREAS TF-11 Biomass Data over the SSA-Fen
BOREAS TF-11 CO2 and CH4 Concentration Data from the SSA-Fen
BOREAS TF-11 CO2 and CH4 Flux Data from the SSA-Fen
BOREAS TF-11 Decomposition Data over the SSA-Fen
BOREAS TF-10 NSA-Fen Tower Flux and Meteorological Data
2. Investigator(s)
2.1 Investigator(s) Name and Title
Dr. Shashi B. Verma
School of Natural Resource Sciences
University of Nebraska
Dr. Timothy Arkebauer
Department of Agronomy
University of Nebraska
Dr. David Valentine
Dept. of Forest Sciences
University of Alaska
2.2 Title of Investigation
Field Micrometeorological Measurements, Process-Level Studies, and Modeling Of
Methane and Carbon Dioxide Fluxes in a Boreal Wetland Ecosystem
2.3 Contact Information
Contact 1:
Micrometeorological Data
Dr. Shashi B. Verma
School of Natural Resource Sciences
University of Nebraska
Lincoln, NE
(402) 472-6702
agme009@unlvm.unl.edu
Contact 2:
Andy Suyker
School of Natural Resource Sciences
University of Nebraska
Lincoln, NE
(402) 472-2168
agme018@unlvm.unl.edu
Contact 3:
K. Fred Huemmrich
University of Maryland
NASA GSFC
Greenbelt, MD
(301) 286-4862
(301) 286-0239 (fax)
Karl.Huemmrich@gsfc.nasa.gov
3. Theory Of Measurements
Micrometeorological Flux Measurements
Flux measurements were made using the eddy correlation technique. This
technique is well established and has been used in many previous field studies
(e.g., Kanemasu et al., 1979; Businger, 1986; Baldocchi et al., 1988; Verma et
al., 1992). The eddy correlation method allows for direct measurement of
vertical turbulent fluxes at a point above the surface. The measurement at this
point, however, represents the integrated effects of a large surface area upwind
of the measurement point. In the eddy correlation method, the flux of a
quantity is calculated from the covariance of the fluctuations of the vertical
wind velocity (w) with the fluctuations of the concentration of interest. For
example:
____
Sensible Heat Flux H = rho Cp w'T'
______
Latent Heat Flux LE = L w'rhov'
_______
Carbon Dioxide Flux Fc = w'rhoc'
_______
Methane Flux Fm = w'rhom'
____
Momentum Flux tau = rho w'u'
where T is air temperature, rhov is the absolute humidity of water vapor, rhoc
is the atmospheric density of carbon dioxide, rhom is the atmospheric density of
methane, u is the horizontal wind velocity, rho is the density of air, Cp is the
specific heat of air at constant pressure, and L is the latent heat of
vaporization. The (') indicates deviation from the mean, and the overbar
indicates a time average.
It is desirable for eddy correlation sensors to be small, aerodynamically
smooth, and symmetric about the horizontal plane of measurement, and to have a
fast response time (< 0.1 s). It is also desirable to have sensors located
close together and to have the sensors mounted on an aerodynamically smooth,
rigid platform. The specifications for some of these requirements will depend
on the measurement height. Further theoretical details of the eddy correlation
method can be found in the following references: Kanemasu et al., 1979;
Businger, 1986; Baldocchi et al., 1988.
Corrections for inadequate sensor frequency response (Moore, 1986) and air
density effects (Webb et al., 1980) are applied to the eddy correlation
measurements.
Filling in Missing Eddy Fluxes of CO2 and Sensible and Latent Heat
During periods of unacceptable wind direction, low wind speed (at night), or
eddy correlation sensor malfunction, fluxes of CO2 and sensible and latent heat
were filled in. For missing periods during daytime, the CO2 flux was filled in
using relationships between CO2 flux and incident photosynthetically active
radiation (PAR) established for different temperature/humidity conditions
throughout the season. Nighttime CO2 flux was filled in using relationships
between CO2 flux (measured on nearby nights during acceptable wind conditions)
and soil temperature. Daytime sensible and latent heat fluxes were estimated
using linear relationships between these fluxes (measured on nearby days under
acceptable conditions) with net radiation. Nighttime sensible and latent heat
fluxes were estimated using the data on temperature and humidity gradients, net
radiation, and soil heat flux in the Bowen ratio-energy balance approach.
During the nighttime periods where the Bowen ratio was unacceptable, fluxes were
interpolated.
4. Equipment
4.1 Sensor/Instrument Description
4.1.1 Collection Environment
Measurements were collected from mid-May through early-October of 1994 and 1995.
Over that time period, temperature conditions ranged from below freezing to over
30�C.
4.1.2 Source/Platform
Eddy Correlation Sensors:
A bracket holding eddy correlation instrumentation was deployed from the side of
3.5-m-high scaffolding. The scaffolding was mounted on a metal framework base
and was guyed. The instruments were at a height of approximately 4.2 m.
Description of Eddy Correlation Instrumentation:
Longitudinal, lateral and vertical wind velocity components (u, v, and w) were
measured with a 3-D sonic anemometer (15-cm path lengths). Vertical wind
velocity fluctuations were also measured with single-axis sonic anemometers (10-
and 20-cm path length). Temperature fluctuations were measured with fine wire
thermocouples (0.0005 in., chromel-constantan). Absolute humidity fluctuations
were measured using an open path Krypton hygrometer. Carbon dioxide density
fluctuations were measured using a closed path, differential infrared
spectrometer. Methane concentration fluctuations were measured using a closed
path tunable diode laser spectrometer (TDLS).
Supporting Meteorological Sensors:
Most supporting instrumentation was attached to metal pipes sunk into the peat.
Description of Supporting Meteorological Instrumentation:
Mean air temperatures were measured with platinum resistance temperature devices
(RTD) and thermistors. Mean relative humidities were measured with capacitive
polymer H chip humidity sensors. Mean horizontal wind velocity was measured
using a cup anemometer. Soil heat flux/storage was measured with heat flux
transducers and temperature sensors. Soil temperatures were measured with
thermistors. Solar radiation was measured with a pyranometer. Reflected solar
radiation was measured with an inverted pyranometer. PAR was measured with a
quantum sensor. Reflected PAR was measured with an inverted point quantum
sensor. Net radiation was measured with a rigid dome net radiation sensor.
Precipitation was measured with electronic recording tipping bucket rain gauges.
Atmospheric pressure was measured with an aneroid barometer. Wind direction was
measured with a wind vane with its null point set to north. The water table was
measured using a float/pulley system where the pulley turned a potentiometer.
4.1.3 Source/Platform Mission Objectives
The objective of the towers and supporting rods was to support the instruments.
4.1.4 Key Variables
Data collected included incoming solar radiation, reflected solar radiation,
incoming PAR, net radiation, latent heat flux, sensible heat flux, carbon
dioxide flux, methane flux, horizontal wind speed at 4 m, soil temperature at 20
cm depth, soil temperature at 10 cm depth, air temperature at 4 m, absolute
humidity at 4 m, vapor pressure deficit at 4 m, atmospheric pressure, wind
direction, precipitation, and water table height above a reference hollow
surface.
4.1.5 Principles of Operation
Both the 1-D and 3-D sonic anemometers determine the wind speed from the
difference in travel times of ultrasonic sound pulses transmitted from opposing
ends of the measurement path.
The Krypton hygrometer measures atmospheric humidity by relating it to the
amount of radiation absorbed by the volume of air in the measurement path. The
amount of radiation absorbed is related to the humidity through calibration.
The TDLS CH4 sensor and the closed path H2O/CO2 measure the concentrations of
methane and water vapor/carbon dioxide as functions of the amount of radiation
absorbed in the measurement path. The amount of radiation absorbed by the
constituent in question is determined from the difference in radiation absorbed
from two radiation wave bands, one that is absorbed by the constituent and a
second that is absorbed by reference gas with a known constituent concentration.
Calibration with known concentration gases provides a relationship of sensor
output to constituent density.
A fine-wire thermocouple measures temperature fluctuations from the
electromotive force (emf) produced at a chromel-constantan thermocouple
junction. The thermocouple is referenced to a junction whose mean temperature
varies with the ambient.
The wind vane is a potentiometer whose output is related to the wind direction.
The thermistors and platinum RTDs used to measure air and peat temperatures
relate changes in resistance to temperature.
Transducers all derive their output from differential thermopiles. The net
radiometer relates the temperature difference of upward and downward facing
blackbody surfaces to net radiation. The pyranometer relates incoming solar
radiation to the temperature difference of blackbody and reflective, upward
facing surfaces whose impinging radiation is restricted to shortwave radiation.
Soil heat flux transducers relate soil heat flux to the temperature difference
between the top and bottom sides of a plate that is inserted in the soil and has
a thermal conductivity similar to that of the surrounding soil.
The PAR sensors relate the cosine-corrected voltage output of a silicon
photodiode to the radiation received in the 400- to 700-nm waveband.
The capacitive polymer H chip's voltage output is linearly related to
atmospheric relative humidity. The output is derived from changes caused by
water vapor upon a thin film capacitor. A thin, water vapor permeable membrane
filter covers the capacitor for protective purposes.
Both the cup anemometer and tipping bucket rain gauge operate by producing
electrical pulses that are counted and related to the value of the quantity
being observed. Both sensors need to be maintained in a level position.
The barometer translates the expansion of a closed cell due to changes in static
atmospheric pressure to a voltage signal.
4.1.6 Sensor/Instrument Measurement Geometry
Eddy Correlation Sensors:
The eddy correlation sensors were mounted on a horizontal bar that was mounted
on a horizontal, rotatable plate. The bar was mounted tangentially to the plate
and approximately 30 cm from the closest edge of the plate. The plate was
rotatable so that the eddy correlation sensors could be rotated into the mean
wind direction. The plate was set on a bracket that attached to the side of a
scaffolding tower. The bracket allowed the plate to slide closer to the tower
for sensor maintenance. With the plate extended, the sensors were approximately
2.5 m from the tower. It was also possible to level the plate (and thus the
sensors) in its extended position.
The eddy correlation sensors were mounted at a height of 4.2 m. The sensor
array contained the 3-D sonic anemometer/thermometer, a fine wire-thermocouple,
and intakes for the closed path CH4 and H2O/CO2 sensors.
Supporting Meteorological Sensors
The atmospheric pressure sensor was mounted at a height of 4.2 m. Mean wind
speed, temperature, and relative humidity sensors were mounted on 1 1/4" steel
pipes sunk about 2.5 m into the peat. The wind vane was mounted atop the cup
anemometer mast. The radiation sensors (solar radiation, reflected solar
radiation, net radiation, PAR, reflected PAR) were mounted on a cross bar, at
1.9 m above the peat surface. The rain gauges were attached to wooden stakes
sunk into the peat. They were mounted at a height of approximately 1 m. The
soil heat flux transducers were installed 0.05 m beneath the surface. The soil
temperature sensors were installed at 0.10 and 0.20 m beneath the surface.
The access to eddy correlation sensors was via a raised walkway, while the
access to most other sensors was via planks laid on the peat surface.
4.1.7 Manufacturer of Sensor/Instrument
Micrometeorological Sensors
3-D sonic anemometer/thermometer
Advanced Technologies, Inc.
6395 Gunpark Dr. Unit E
Boulder, CO 80301
(303) 530-4977
Single axis sonic anemometer/thermometer
Kaijo Denki Co., Ltd.
No 19.1 Chrome Kanda-Nishikicho
Chiyoda-Ku
Tokyo 101
Japan
Fine-wire thermocouples
Campbell Scientific
P.O. Box 551
Logan, UT 84321
(801) 753-2342
(801) 752-3268 (fax)
Lyman alpha hygrometer
Atmospheric Instrumentation Research, Inc.
1880 South Flatiron Court
Boulder, CO 80301
(303) 499-1701
(303) 499-1767 (fax)
Closed path H2O/CO2 sensor
LI-COR, Inc.
4421 Superior Street
P.O. Box 4425
Lincoln, NE 68504
(402) 467-3576
(402) 467-2819 (fax)
Closed path tunable diode laser spectrometer (TDLS) CH4 sensor
Unisearch Associates, Inc.
222 Snidercroft Rd.
Concord, Ontario
CANADA
L4K 1B5
(416) 669-2280
(416) 669-5132 (fax)
Platinum RTDs for air temperature
Omega Engineering, Inc.
One Omega Dr.
Box 4047
Stamford, CT 06907-0047
(203) 359-1660
(203) 359-7900 (fax)
Vaisala chemical relative humidity/RTD air temperature sensors
Campbell Scientific
P.O. Box 551
Logan, UT 84321
(801) 753-2342
(801) 752-3268 (fax)
Cup anemometers
Cayuga Development
15 Hickory Circle
Ithaca, NY
(607) 272-8599
Soil heat flux transducers
Radiation & Energy Balance Systems, Inc.
P.O. Box 15512
Seattle, WA 98115-0512
(206) 488-9404
Bead thermistors for soil temperature
Omega Engineering, Inc.
One Omega Dr.
Box 4047
Stamford, CT 06907-0047
(203) 359-1660
(203) 359-7900
15-cm platinum RTD bars for soil temperature
Omega Engineering, Inc.
One Omega Dr.
Box 4047
Stamford, CT 06907-0047
(203) 359-1660
(203) 359-7900 (fax)
Pyranometer
The Eppley Laboratory, Inc.
12 Shefield Ave.
P.O. Box 419
Newport, RI 02840
(401) 847-1020
(401) 847-1031 (fax)
Point quantum PAR sensors
LI-COR, Inc.
4421 Superior Street
P.O. Box 4425
Lincoln, NE 68504
(402) 467-3576
(402) 467-2819 (fax)
Net radiation sensor
Radiation & Energy Balance Systems Inc.
P.O. Box 15512
Seattle, WA 98115-0512
(206) 488-9404
Tipping bucket rain gauges
Campbell Scientific
P.O. Box 551
Logan, UT 84321
(801) 753-2342
(801) 752-3268 (fax)
Wind vane
Campbell Scientific
P.O. Box 551
Logan, UT 84321
(801) 753-2342
(801) 752-3268 (fax)
Static pressure sensor
Alan Bedard
NOAA
Boulder, CO
(303) 497-6508
4.2 Calibration
4.2.1 Specifications
Calibration Sources
Eddy Correlation Instrumentation:
1-D sonic anemometer: Supplied by manufacturer
3-D sonic anemometer: Supplied by manufacturer
Thermocouples: Supplied by manufacturer
Lyman alpha hygrometer: Calibrated with dew point generator, RTD
Closed cell H2O: Calibrated with dew point generator, RTD
Closed cell CO2: Field calibration using known standard gases
Closed cell CH4: Field calibration using known standard gases
Supporting Meteorological Instrumentation:
Mean air temperature nickel-iron (NIFe) RTDs: Calibrated in water bath
Mean air temperature thermistors: Supplied by manufacturer
Mean relative humidity: Supplied by manufacturer
Cup anemometers: Calibrated in wind tunnel
Soil heat flux plates: Supplied by manufacturer
Soil temperature bead thermistors: Calibrated in water bath
Pyranometer: Supplied by manufacturer
PAR quantum sensors: Supplied by manufacturer
Net radiation sensors: Supplied by manufacturer
Tipping bucket rain gauges: Supplied by manufacturer
Wind vane: Supplied by manufacturer
Atmospheric pressure sensors: Supplied by manufacturer
Water table sensor: Supplied by manufacturer
4.2.1.1 Tolerance
Eddy correlation instrumentation
1-D sonic anemometer:
Path length : 20 cm
Sampling frequency : 20 Hz
Data frequency : 10 Hz
Accuracy : 1 %
Resolution : 0.005 m/s
3-D sonic anemometer:
Path length : 15 cm
Sampling frequency : Hz
Data frequency : 10 Hz
Accuracy : 0.05 m/s
Resolution : 0.01 m/s
Fine wire thermocouples:
Dimension : 0.0005 in
Time response : 0.008 s
Lyman alpha hygrometer:
Radiation source : UH2
Path length : 0.5 cm
Time response : 2 ms
Accuracy : 4 %
Resolution : 2 %
Closed cell H2O/CO2 sensor:
Path length : 15 cm
Sample cell volume : 11.9 cm3
Sample cell pressure : 850 mb
Time response : 0.06 s
Sampling frequency : 500 Hz
Accuracy : 3 ppm
Resolution : 2 ppm
Closed cell CH4 sensor:
Path length : 53 m
Sample cell volume : 0.4 L
Sample cell pressure : 40 Torr
Sampling frequency : 0.15 �sec
Data output frequency : 10 Hz
Accuracy : 2 %
Resolution : 15 ppb
Supporting Instrumentation:
Air temperature thermistors:
Linearization error : 0.1 C
Relative humidity sensors:
Accuracy : 2 %
Response time : 15 s
Temperature-induced error : 0.04 % RH/C
PAR quantum sensors:
Accuracy : 5 %
Sensitivity :0.005 A/mole/s/m2
Linearity : 1 %
Tipping bucket rain gauges:
Accuracy : 1 %
Resolution : 0.1 mm
Sensor specifications are currently unavailable for these sensors:
Air temperature NIFe RTDs
Soil temperature bead thermistors
Pyranometer
Net radiation sensors
Cup anemometers
Soil heat flux plates
Wind vane
Atmospheric pressure sensor
Water table sensor
4.2.2 Frequency of Calibration
Eddy Correlation Instrumentation:
Lyman alpha hygrometer: Calibrated monthly
Krypton hygrometer: Calibrated monthly
Closed cell H2O sensor: Calibrated at beginning and end of season
Closed cell CO2 sensor: Calibrated twice daily
Closed cell CH4 sensor: Calibrated twice daily
Supporting Meteorological Instrumentation:
Mean air temperature NIFe RTDs: Calibrated prior to season
Mean air temperature thermistors: Calibrated prior to season
Mean relative humidity: Calibrated by manufacturer
Cup anemometers: Calibrated prior to season
Soil heat flux transducers: Calibrated by manufacturer
Soil temp. bead thermistors: Calibrated prior to season
Soil temp. platinum RTD: Calibrated prior to season
Pyranometer: Calibrated prior to season
PAR quantum sensors: Calibrated prior to season
Net radiation sensors: Calibrated prior to season
Atmospheric pressure : Calibrated prior to season
Water table: Calibrated by manufacturer
4.2.3 Other Calibration Information
The humidity source used to calibrate the eddy correlation water vapor sensors
is a LI-COR LI-620 dew point generator, available from LI-COR, Inc., P.O. Box
4425, Lincoln, NE 68504 (phone 402-467-3576, fax 402-467-2819).
Calibration gases for the eddy correlation CO2 sensors were obtained from
Acklands, 1402 Quebec Ave., Saskatoon, Sask. CANADA, S7K 1V5 (Primary supplier:
Linde gas, Alberta, CANADA). These gases were calibrated against gases of
known concentration traceable to the National Oceanic and Atmospheric
Administration (NOAA), Boulder, CO.
Calibration gases for the TDLS CH4 sensor were compressed air obtained from
Acklands, 1402 Quebec Ave., Saskatoon, Sask. CANADA, S7K 1V5. The compressed
air gases were calibrated against gases of known concentration obtained from
Matheson Gas Products, P.O. Box 96, Joliet IL, 60434.
Cup anemometers were calibrated in the University of Iowa wind tunnel. A pitot
tube anemometer was used as a standard.
5. Data Acquisition Methods
Eddy Correlation
Eddy correlation signals were low-pass filtered with 8-pole Butterworth active
filters (12.5-Hz cutoff frequency) and sampled at 25 Hz. These signals were
recorded to optical disks. Means, variances, and covariances were calculated on
a half-hourly basis.
Supporting Meteorological Measurements
Signals from the supporting instrumentation were recorded using a Campbell
CR21X. Half-hourly averages of these signals were calculated. The averaged
values were retrieved from the CR21X data loggers using a PC microcomputer.
6. Observations
6.1 Data Notes
None.
6.2 Field Notes
The forest to the east of the fen has been harvested within the past 5 years.
However, a band of forest 50 to several hundred meters wide separates the fen
from the harvested area.
The instrumentation platforms are located approximately 50 m west of the eastern
edge of the fen. On the western edge there is a more gradual change from open
fen to tamarack to black spruce forest. The transition from fen to forested land
is more abrupt on the eastern edge of this fen.
Within the directions of acceptable fetch, the best fetch is in the west to
north directions. In the south to west directions there are some small stands
(strings) of tamarack/black spruce.
Data collection was interrupted from 01- to 20-Jun-1995 because of a nearby
forest fire.
7. Data Description
7.1 Spatial Characteristics
7.1.1 Spatial Coverage
All measurements were collected at the SSA-Fen site. North American Datum of
1983 (NAD83) coordinates for the site are latitude 53.80206� N, longitude
104.61798� W, and elevation of 524.7 m above sea level.
7.1.2 Spatial Coverage Map
Not applicable.
7.1.3 Spatial Resolution
Eddy correlation measurements were made at a height of 4.2 m. For this
instrument height, the measurements apply to a surface "footprint" (Schuepp et
al., 1990; Leclerc and Thurtell, 1990) extending up to about 420 m upwind of the
tower, depending upon the meteorological conditions. Adequate upwind fetch was
available only in the south through west to north-northeast directions; other
directions were inhabited by forest.
7.1.4 Projection
None.
7.1.5 Grid Description
None.
7.2 Temporal Characteristics
7.2.1 Temporal Coverage
Data were collected during the periods:
23-Aug to 11-Sep-1993
18-May 18 to 07-Oct-1994
18-May 18 to 09-Oct-1995
Note: Data collection was interrupted from 01- to 20-Jun-1995 because of a
nearby forest fire.
7.2.2 Temporal Coverage Map
None.
7.2.3 Temporal Resolution
The values are half-hour averages except for rainfall, which is a half-hour
total.
7.3 Data Characteristics
Data characteristics are defined in the companion data definition file
(tf11tfx.def).
7.4 Sample Data Record
Sample data format shown in the companion data definition file (tf11tfx.def).
8. Data Organization
8.1 Data Granularity
All fen tower flux data are in one file.
8.2 Data Format
The data files contain American Standard Code for Information Interchange
(ASCII) numerical and character fields of varying length separated by commas.
The character fields are enclosed with single apostrophe marks. There are no
spaces between the fields. Sample data records are shown in the companion data
definition file (tf11tfx.def).
9. Data Manipulations
9.1 Formulae
Voltage to Signal Conversion Formulae
All sensors except Krypton hygrometer: X = a + b*V
Krypton hygrometer: X = a + b*ln(V)
9.1.1 Derivation Techniques and Algorithms
None.
9.2 Data Processing Sequence
Eddy Correlation Data
a) Convert voltages to variables (e.g., temperature, velocity) using
calibration equations.
b) High pass filter the signals to remove low-frequency noise.
c) Calculate means, standard deviations, and covariances.
d) Calculate cospectral values.
e) Make adjustments to values as appropriate (see section 9.3).
Supporting Meteorological Data
a) Convert voltages to variables (e.g., temperature, velocity) using
calibration equations.
b) Calculate means.
c) Make adjustments to values as appropriate (see section 9.3).
9.2.1 Processing Steps
None given.
9.2.2 Processing Changes
None.
9.3 Calculations
Eddy Correlation Flux Calculation
Sums of squares and sums of products of signals are calculated during a half-
hour run. From these values, variances and covariances can be calculated. In
the eddy correlation method, the flux of a quantity is calculated from the
covariance of the fluctuations of the vertical wind velocity (w) with the
fluctuations of the concentration of interest. For example:
____
Sensible Heat Flux H = rho Cp w'T'
_______
Latent Heat Flux LE = L w'rhov'
_______
Carbon Dioxide Flux Fc = w'rhoc'
_______
Methane Flux Fm = w'rhom'
____
Momentum Flux tau = rho w'u'
where T is air temperature, rhov is the absolute density of water vapor, rhoc is
the absolute density of carbon dioxide, rhom is the absolute density of methane,
u is the horizontal wind velocity, rho is the density of air, Cp is the specific
heat of air at constant pressure, and L is the latent heat of vaporization. The
(') indicates deviation from the mean, and the overbar indicates a time
average.
Adjustments to Results
Frequency Response Correction: A correction is needed to adjust for inadequate
frequency response. This correction was applied in a manner similar to that
given in Moore (1986).
Correction for Nonspecific Sensor Absorption: The closed path CO2 sensor has a
slight response to water vapor. This adjustment is made based on information
supplied by the manufacturer.
Correction for Air Density Effects: Generally, corrections are made to the
fluxes of gases, such as CO2 and CH4, for the effect of water vapor and
temperature on the density of the air being sampled. The use of insulated, metal
intake tubing for closed path sensors helped remove most of the temperature
fluctuations. For the signals from the closed path CO2 and CH4 sensors,
adjustments were made for density fluctuations caused by fluctuating water vapor
concentrations. Signals from the open path water vapor sensor were adjusted for
density fluctuations caused by fluctuating temperature. These corrections are
made following a procedure given in Webb et al. (1980).
9.3.1 Special Corrections/Adjustments
None.
9.3.2 Calculated Variables
None.
9.4 Graphs and Plots
None.
10. Errors
10.1 Sources of Error
Electronic Noise
Although all sensors were subject to small amounts of high frequency electronic
noise, most of this was removed from eddy correlation sensor signals by the low-
pass filters prior to recording the raw data. Sensors with noise in lower
frequency regions (e.g., occasional spiking) were repaired/adjusted and their
data were generally removed from the data set. It is possible that such noise
may occasionally be present in some of the data.
Calibration Drift
The CO2, CH4, and H2O sensors may have been subject to some calibration drift.
These sensors were calibrated and linear interpolations were used in data
processing.
Dew/Wetness
Dew or rain caused aberrant signals in some sensors (net radiometers, PAR
quantum sensors, Lyman-alpha hygrometer, sonic anemometers, and fine wire
thermocouples). Generally, heavy dew or rain would cause complete deterioration
of these signals. Periods during which dew or rain occurred were noted and used
in the quality control of data.
10.2 Quality Assessment
10.2.1 Data Validation by Source
A field log book was kept, in which occurrences that may have affected results
were recorded. These notes were later scrutinized and converted to a numerical
format that could be incorporated into the data set and used in quality control
of the data. Comparison of results from alternate sensors (or alternate
methods) was also employed in determining the quality of results.
10.2.2 Confidence Level/Accuracy Judgment
The data set is of generally good quality.
10.2.3 Measurement Error for Parameters
SOLAR_RAD_IN +/- 1 %
PAR_IN +/- 7 %
R_NET +/- 4 to 7 %
LE_FLUX_MEASURED +/- 15 %
H_FLUX_MEASURED +/- 15 %
CO2_FLUX_MEASURED +/- 0.01 �mol m-2 s-1
CH4_FLUX +/- 0.4 mg m-2 h-1
HORIZ_WIND_SPEED_4M +/- 0.2 m s-1
SOIL_TEMP_-20CM +/- 0.1 �C
SOIL_TEMP_-10CM +/- 0.1 �C
AIR_TEMP_4M +/- 0.1 �C
VAP_PRESS_DEF_4M +/- 0.1 kPa
WATER_TABLE +/- 0.005 m
10.2.4 Additional Quality Assessments
None.
10.2.5 Data Verification by Data Center
Data were examined to check for spikes, values that are four standard deviations
from the mean, long periods of constant values, and missing data.
11. Notes
11.1 Limitations of the Data
There are no known limitations in these data.
11.2 Known Problems with the Data
See Section 10.1.
11.3 Usage Guidance
Errors in the micrometeorological data set are indicated by the value -999.00.
11.4 Other Relevant Information
None.
12. Application of the Data Set
These data are useful for the study of water, energy, and carbon exchange in
boreal wetlands.
13. Future Modifications and Plans
None.
14. Software
14.1 Software Description
None given.
14.2 Software Access
None given.
15. Data Access
These data are available from the Earth Observing System Data and Information
System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive
Center (DAAC). BOREAS data may be downloaded through the ORNL World Wide Web
site or a complete set of BOREAS CD-ROMs may be ordered from the ORNL DAAC User
Services Office.
ORNL DAAC User Services
Oak Ridge National Laboratory
(865) 241-3952
ornldaac@ornl.gov
ornl@eos.nasa.gov
16. Output Products and Availability
16.1 Tape Products
None.
16.2 Film Products
None.
16.3 Other Products
The data are available as tabular ASCII text files.
17. References
17.1 Platform/Sensor/Instrument/Data Processing Documentation
None.
17.2 Journal Articles and Study Report
Baldocchi, D.D., B.B. Hicks, and T.P. Meyers. 1988. Measuring biosphere-
atmosphere exchanges of biologically related gases with micrometeorological
methods. Ecology, 69:1331-1340.
Businger, J.A. 1986. Evaluation of the accuracy with which dry deposition can be
measured with current micrometeorological techniques. J. Clim. and Appl.
Meteorol. 25:1100-1124.
Kanemasu, E.T., M.L. Wesely, B.B. Hicks, and J.L. Heilman. 1979. Techniques for
calculating energy and mass fluxes. In: Modification of the Environment of
Crops. B.L. Barfield and J.F. Gerber, (eds.), Amer. Soc. of Agri. Eng. St.
Joseph,. MO. P. 156-182.
Leclerc, M.Y. and G.W. Thurtell. 1990. Footprint prediction of scalar fluxes
using a Markovian analysis. Boundary-Layer Meteorology. 52:247-258.
Moore, C.J. 1986. Frequency Response Corrections for Eddy Correlation Systems.
Boundary-Layer Meteorology. 37:17-35.
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. Boundary Layer Meteorology 50:355-373.
Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment
Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94).
Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J.
Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E.
Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and
early results from the 1994 field year. Bulletin of the American
Meteorological Society. 76(9):1549-1577.
Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere
Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94).
Sellers, P. and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment
Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96).
Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere
Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96).
Sellers, P.J., F.G. Hall, R.D. Kelly, A. Black, D. Baldocchi, J. Berry, M. Ryan,
K.J. Ranson, P.M. Crill, D.P. Lettenmaier, H. Margolis, J. Cihlar, J.
Newcomer, D. Fitzjarrald, P.G. Jarvis, S.T. Gower, D. Halliwell, D. Williams, B.
Goodison, D.E. Wickland, and F.E. Guertin. 1997. BOREAS in 1997:
Experiment overview, scientific results, and future directions. Journal of
Geophysical Research 102(D24):28731-28769.
Suyker, A.E., S.B. Verma, and T.J. Arkebauer. 1997. Season-long measurement of
carbon dioxide exchange in a boreal fen. Journal of Geophysical Research
102(D24):29021-29028.
Verma, S.B., F.G. Ullman, D. Billesback, R.J. Clement, J. Kim,, and E.S. Verry.
1992. Eddy correlation measurements of methane flux in a northern peatland
ecosystem. Boundary Layer Meteorology 58:289-304.
Webb, E.K., G.I. Pearman, and R. Leuning. 1980. Correction of flux measurements
for density effects due to heat and water vapour transfer. Quart. J. Roy.
Meteorol. Soc. 106:85-100.
17.3 Archive/DBMS Usage Documentation
None.
18. Glossary of Terms
None.
19. List Of Acronyms
AES - Atmospheric Environment Services
ASCII - American Standard Code for Information Interchange
BOREAS - BOReal Ecosystem-Atmosphere Study
BORIS - BOREAS Information System
CD-ROM - Compact Disk-Read Only Memory
CGR - Certified by Group
Cp - Specific heat of air at constant pressure
CPI - Certified by PI
CPI-??? - Certified but questionable
DAAC - Distributed Active Archive Center
e - Air vapor pressure
emf - electromotive force
EOS - Earth Observing System
EOSDIS - EOS Data and Information System
GMT - Greenwich Mean Time
GSFC - Goddard Space Flight Center
HTML - HyperText Markup Language
NASA - National Aeronautics and Space Administration
NOAA - National Oceanic and Atmospheric Administration
NSA - Northern Study Area
ORNL - Oak Ridge National Laboratory
p - Atmospheric pressure
PANP - Prince Albert National Park
PAR - Photosynthetically Active Radiation
PPB - Parts per billion
PPFD - Photosynthetic Photon Flux Density
PRE - Preliminary
rho - Air density
Rhom - Absolute Atmospheric density of methane
RTD - Resistance Temperature Device
SSA - Southern Study Area
T - Air temperature
TDLS - Tunable Diode Laser Spectrometer
TF - Tower Flux
URL - Uniform Resource Locator
z - Height or depth
20. Document Information
20.1 Document Revision Date
Written: 01-Oct-1997
Last Updated: 11-Dec-1998
20.2 Document Review Date(s)
BORIS Review: 03-Dec-1998
Science Review:
20.3 Document ID
20.4 Citation
When using these data please include the following acknowledgment:
Micrometeorological data were collected by Dr. Shashi B. Verma and his
colleagues of the University of Nebraska-Lincoln,
as well as citations of relevant papers, see section 17.2.
If using data from the BOREAS CD-ROMs please also reference the data as:
[Investigators Names (see section 2.1)],"[Title of Investigation (see section
2.2)]." in Collected Data of The Boreal Ecosystem-Atmosphere Study. Eds. J.
Newcomer, D. Landis, S. Conrad, S. Curd, K. Huemmrich, D. Knapp, A. Morrell, J.
Nickeson, D. Rinker, R. Strub, T. Twine, F. Hall, and P. Sellers. CD-ROM. NASA,
1999.
Replacing the phrases in square brackets with the information from the noted
document sections.
To cite the BOREAS CD-ROM set as a published volume, use:
J. Newcomer, D. Landis, S. Conrad, S. Curd, K. Huemmrich, D. Knapp, A. Morrell,
J. Nickeson, D. Rinker, R. Strub, T. Twine, F. Hall, and P. Sellers, eds.
Collected Data of The Boreal Ecosystem-Atmosphere Study. CD-ROM. NASA, 1999.
20.5 Document Curator
20.6 Document URL
Keywords
FEN
WETLAND
TOWER FLUX
METEOROLOGY
SENSIBLE HEAT FLUX
LATENT HEAT FLUX
CARBON DIOXIDE FLUX
METHANE FLUX
PHOTOSYNTHETIC PHOTON FLUX DENSITY
PHOTOSYNTHETICALLY ACTIVE RADIATION
PPFD
PAR
NET RADIATION
AIR TEMPERATURE
SOIL TEMPERATURE
VAPOR PRESSURE
WIND SPEED
RAINFALL
TF11_Fen_Flux.doc
01/13/99