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 µsec 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 µmol 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