BOREAS TGB-04 NSA-BP Tower Flux and Meteorological Data Summary The BOREAS TGB-04 team measured the exchange of heat, water, and CO2 between a boreal forest beaver pond and the atmosphere in the NSA for the ice-free period of BOREAS. The data cover the period of May 28 to September 18, 1994. The data are available in tabular ASCII files. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 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 Modifications 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 TGB-04 NSA-BVP Tower Flux and Meteorological Data 1.2 Data Set Introduction This data set includes heat, CO2, and water vapor fluxes measured from the BOReal Ecosystem-Atmosphere Study (BOREAS) Northern Study Area (NSA)-Beaver Pond (BVP) tower. Anemometer, temperature (wet and dry bulb), and CO2 profile measurements were collected from a tower located in the middle of a beaver pond. These data along with radiometric measurements were used to calculate the surface turbulent fluxes using the profile and energy balance technique. Measurements of the water level, flow rates, and light penetration of the beaver pond were also collected. 1.3 Objective/Purpose The objective of this study was to quantify the exchange of heat, water, and CO2 between boreal forest beaver ponds and the atmosphere for the ice-free period of BOREAS. The fluxes of heat, water and CO2 from one beaver pond were measured continuously using the energy balance Bowen ratio approach. The diffuse and bubble flux CH4 were measured several times a week using chambers. The chamber approach was used to sample CO2 and CH4 flux from four to five additional beaver ponds, once every 2 weeks, and regional surveys of the surface concentrations of CO2, CH4, and dissolved organic carbon (DOC) were carried out on accessible beaver ponds. 1.4 Summary of Parameters Variables measured include latent heat flux, sensible heat flux, soil heat flux, CO2 flux, net radiation, incident and reflected Photosynthetically Active Radiation (PAR), underwater PAR, incident and reflected solar radiation, wind speed and direction, precipitation amount, air temperature, vapor pressure, air pressure, flow rate of water out of the pond, and water table height. 1.5 Discussion In BOREAS, each surface flux station 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 beaver pond to make measurements of the fluxes of CO2, CH4, and the energy budget components. These fluxes were considered important in characterizing wetlands of the boreal forest. The surface fluxes were measured using the profile and energy balance technique. Supporting meteorological measurements were also made at this site. 1.6 Related Data Sets BOREAS TGB-01 CH4 Concentration and Flux Data from NSA Tower Sites BOREAS TF-10 NSA-Fen Tower Flux and Meteorological Data BOREAS TF-11 SSA-Fen Tower Flux and Meteorological Data 2. Investigator(s) 2.1 Investigator(s) Name and Title Dr. N.T. Roulet Department of Geography McGill University 2.2 Title of Investigation The Fluxes of Energy and Trace Gases from Beaver Ponds and Dry Upland Forest Floor in the NSA 2.3 Contact Information Contact 1: Dr. N.T. Roulet Department of Geography McGill University Montreal, Quebec, Canada (514) 398-4945 (514) 398-7437 (fax) roulet@felix.geog.mcgill.ca Contact 2: 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 A four-level profile measurement system of temperature, wind speed, humidity, and C)2 were used to calculate the flux of sensible heat, momentum, latent heat, and C)2, respectively, from a tower located in the middle of a beaver pond. According to well-accepted footprint theory, the tower was sufficiently low to the ground to obtain flux measurements representative of the pond and not the surrounding forested area. Differential measurements between levels were then used to calculate the actual fluxes based upon the well-proven profile technique. 4. Equipment 4.1 Sensor/Instrument Description Instrumentation at this site was fairly elaborate. The basis of the system was the Campbell Scientific CR7 data logger, which controlled operation and saved incoming data for later analysis. Also included was a LI-COR model 6252 CO2 analyzer capable of measuring CO2 concentrations at a fast sampling rate. Measurements were collected from a short tower using a profile system at 25 cm, 50 cm, 100 cm, and 150 cm above the pond surface. Gas sampling locations were switched automatically by the data logger, allowing sufficient time to purge the sampling lines of the previous level's air before a measurement was taken. Due to the fluctuating nature of the pond surface height, continuous measurements were made of its movement (by potentiometer). The surface heights were then used to correct the actual height of the instruments above the water surface as this greatly affects the calculated fluxes. 4.1.1 Collection Environment Measurements were collected from the end of May through mid-September of 1994. Over that time period, temperature conditions ranged from slightly below freezing to about 28 °C. 4.1.2 Source/Platform A ground-based platform was situated on a stable dock-like structure in the center of the pond. It was accessible by a floating boardwalk. The tower was mounted on this dock, and the profile instruments were placed at the appropriate levels and wired back to a low-profile instrument box also on this dock. Within this box were the data logger, CO2 analyzer, gas sampler switching system (from one level to the next), and power supply panel and converter from 120V AC to 12V DC. 4.1.3 Source/Platform Mission Objectives The mission objective was to collect continuous energy balance and CO2 fluxes from an active beaver pond surface. 4.1.4 Key Variables Profile measurements, all at 0.25, 0.5, 1.0, and 1.5 m: Temperature (using thermocouples) Moisture (using thermocouples and wet/dry bulb technique) Wind speed CO2 concentration CH4 concentration Nonprofile measurements: Water table measurements referenced to lowest instrument profile level (0.25 m) Incoming solar radiation (up-facing pyranometer) Outgoing solar radiation (down-facing pyranometer) Net radiation (all-wave radiometer) Water temperature profile (1 cm, 5 cm, 10 cm, 20 cm) (using thermocouples) Atmospheric pressure at surface Incoming PAR Outgoing PAR Wind direction Precipitation Underwater PAR 4.1.5 Principles of Operation The calculation of fluxes required a calculation based upon measured momentum flux. Wind speed profiles determine the momentum flux toward the surface and the associated transfer coefficient Km is calculated and corrected for stability by temperature profile measurements. Using similarity theory, the same transfer coefficient is applied to the fluxes of sensible and latent heat, and CO2 using the formula of the form: Flux = K x dA/dz where K is the eddy diffusivity or transfer coefficient, and the second term is the gradient of the entity concerned. A good review of the procedures used is found within Oke (1987), Appendix A2, Section 2b. Given the calculations of sensible and latent heat and measured net, incoming, and outgoing radiation, this allows closure of the energy and surface balance equations by attributing the difference to the ground heat flux (Qg). 4.1.6 Sensor/Instrument Measurement Geometry All profile measurements collected data at heights of 0.25, 0.5, 1.0, and 1.5 m above the water surface when established, with water surface fluctuation accounted for during operation. Wind direction, incoming and outgoing radiation sensors, and net radiation were measured 2 m above established water surface. Atmospheric pressure and precipitation were measured on the tower platform. 4.1.7 Manufacturer of Sensor/Instrument Thermocouples (for both dry and wet bulb): Type T Supplier: Electrosonic, Inc. 1100 Gordon Baker Road Willowdale, Ontario, Canada M2H 3B3 Data Loggers and Multiplexes: Campbell Scientific Canada Corp. 11564-149th Street Edmonton, AB, Canada T5M 1W7 (403) 454-2505 (403) 454-2655 (fax) Water Table Measurement Twenty Turn Bournes Precision Potentiometers Manufactured by: Electrosonic, Inc. 1100 Gordon Baker Road Willowdale, Ontario, Canada M2H 3B3 Anemometry: R.M. Young Company (via Campbell Scientific) Wind direction: R.M. Young Company (via Campbell Scientific) CO2 concentration: LI-COR Model 6252 Gas Analyzer LI-COR, Inc. P.O. Box 4425 Lincoln, NE 68504 (402) 467-3576 Pyranometers: Kipp and Zonen, Model CM11 Net Radiometer: Middleton Atmospheric pressure: Met-One Model 090B-4 (via Campbell Scientific) PAR Sensors: L-ICOR Model 'Quantum' LI-COR, Inc. P.O. Box 4425 Lincoln, NE 68504 (402) 467-3576 Underwater PAR: LI-COR Model 'Underwater' LI-COR, Inc. P.O. Box 4425 Lincoln, NE 68504 (402) 467-3576 Precipitation: Sierra/MISCO, Inc., Tipping bucket model 2501 Sierra/MISCO, Inc. 1825 Eastshore Highway Berkeley, CA 94710 4.2 Calibration Thermocouples: all calibrated before deployment to ensure there were no offsets between the psychrometers. Also, at the end of the field season, all psychrometers were run horizontally to determine if any offsets had developed over the summer. Anemometry: calibrated prior to deployment. Radiometric sensors (net radiation, PAR, solar): calibrated prior to deployment. CO2 gas analyzer: calibrated prior to setup, midsummer, and end of season. Note that for these profile measurements, absolute CO2 concentration need not be exact, since it is the difference between levels that is important to calculate the flux. Water level: a potentiometer and machined aluminum wheel calibrated from previous experiments were used. Weekly manual measurements of water table depth were taken to ensure proper calibration of the electronic measurements which is required to account for the changing heights of the instruments above the water surface. 4.2.1 Specifications Thermocouples: type T thermocouple rated at +/-0.001 °C maximum error Anemometry: rated at 0.1 m/s with a stall speed of 0.1 m/s Wind direction: +/- 2° CO2 concentration: +/-0.1 ppm (0,02 ppm with 15-second averaging time used) Radiometry: approximately +/-1.0 W/m2 Water levels: maximum error of +/-1 mm Precipitation: +/-1 mm Atmospheric pressure: +/-0.01 kPa 4.2.1.1 Tolerance Thermocouples: range allowable: +/-62.5 °C of data logger temperature Anemometry: range: within observable limits CO2 concentration: 0 to 1000 ppm Radiometry: within observable limits Water levels range allowable: large; depends upon length of beaded cable Atmospheric pressure: approximately 90-106 kPa 4.2.2 Frequency of Calibration All instruments were calibrated once, before field deployment, except the gas analyzer, which was also calibrated midsummer and checked again at the end of the field season. 4.2.3 Other Calibration Information No corrections were required according to the calibration methods described above. 5. Data Acquisition Methods Anemometer, temperature (wet and dry bulb), and CO2 profile measurements on the tower, along with radiometric measurements, were used to calculate the surface turbulent fluxes using the profile and energy balance technique. Each of these parameters was measured every 10 seconds and averaged, and then saved on the data logger every 30 minutes. These data were later transferred to computer, where the energy and CO2 flux values were calculated using the standard flux-profile technique. Radiometric, temperature, CO2, and pressure readings were made by differential voltage measurements, which were multiplied by a calibration coefficient at the data logger and saved for later download. A CO2 concentration at each level was determined once very 90 seconds. The data logger controlled switching of the gas sampling ports (at each level) automatically by solenoids, and saved the associated 30-minute average reading for later download. For water level readings, a potentiometer varied the voltage measured by the data logger as the float (or bog shoe) on the beaded cable rose and lowered in response to water table changes. The data logger measured this changing voltage, which was easily converted into the height change since the potentiometers were calibrated to 1 mV of change being equal to 1 mm of vertical water change. This reading was saved and used for the recalculation of instrument heights every 30 minutes. 6. Observations 6.1 Data Notes There are several periods of missing data within this set, due mainly to generator failure. In most cases, these periods are less than 24 hours, since daily visits to check instrumentation were made throughout the field campaign. 6.2 Field Notes None. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage All data were collected at the BOREAS NSA BP site. North American Datum of 1983 (NAD83) coordinates for the site are latitude 55.84225° N, longitude 98.02747° W, and elevation of 186.74 m. 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The tower was set up in the center of a beaver pond complex considered to be representative of this environment according to standard footprint theory. The tower was placed to give a 150-m fetch in all directions except for 310° to 100°. In this section, the fetch was less than 100 m. 7.1.4 Projection None. 7.1.5 Grid Description None. 7.2 Temporal Characteristics The data were collected continuously every 10 seconds for all variables except CO2 concentration, which was collected every 30 seconds. All readings were then averaged over 30 minute intervals (180 and 60 measurements, respectively, for average calculation). 7.2.1 Temporal Coverage The data were collected during the summer of 1994 between the months of May and September. 7.2.2 Temporal Coverage Map None. 7.2.3 Temporal Resolution Resolution is 30 minutes. These represent average values of the previous 30 minutes. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (tgb4flux.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (tgb4flux.def). 8. Data Organization 8.1 Data Granularity All of the NSA-BP Tower Flux and Meteorological Data are contained in one data set. 8.2 Data Format The data file contains 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 format shown in the companion data definition file (tgb4flux.def). 9. Data Manipulations 9.1 Formulae See Section 9.1.1. 9.1.1 Derivation Techniques and Algorithms The calculation of fluxes required later computer calculation based upon measured momentum flux. Wind speed profiles determine the momentum flux toward the surface and the associated transfer coefficient Km is calculated and corrected for stability by temperature profile measurements. Using similarity theory, the same transfer coefficient is applied to the fluxes of sensible and latent heat, and CO2 using the formula of the form: Flux = K x dA/dz where K is the eddy diffusivity or transfer coefficient, and the second term is the gradient of the entity concerned. A good review of the procedures used is found within Oke (1987), Appendix A2, Section 2b. Given the calculations of sensible and latent heat and measured net, incoming, and outgoing radiation, this allows closure of the energy and surface balance equations by attributing the difference to the ground heat flux (Qg). 9.2 Data Processing Sequence 9.2.1 Processing Steps BORIS staff processed these data by: 1) Reviewing the initial data files and loading them online for BOREAS team access. 2) Designing relational data base tables to inventory and store the data. 3) Loading the data into the relational data base tables. 4) Working with the team to document the data set. 5) Extracting the data into logical files. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None. 9.3.2 Calculated Variables The CO2 flux and the latent, sensible, and soil heat fluxes were calculated. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error Instrument error could occur due to wire disconnection or shorting, multiplexer or data logger malfunction, or battery or generator failure. In addition, due to the elaborate nature of calculating fluxes based upon profile measurements, certain theoretical errors can become large in some situations. These situations occur mainly at dusk and overnight when wind speeds become very small and differences in wind speed become negligible over such a short tower. In these cases, the eddy diffusivity can become zero, resulting in a zero flux value. Under these circumstances, our methods would suggest there are no fluxes either up or down, although they must be occurring, but below the sensitivity of ordinary profile system anemometry. In addition, very small gradients of any parameter approaching the limitations of the instrument could also result in an underestimate of the actual existing flux by reducing the gradient to something approaching zero. This may seem important; however, these times occur infrequently, and the fluxes must be quite small. In any case, over a diurnal period the errors associated with the profile technique are not thought to be a significant missing component of the energy or C)2 balance. 10.2 Quality Assessment 10.2.1 Data Validation by Source All data were plotted and checked to determine if there were any outlying points that were obviously incorrect. These points were removed and replaced by -999, which was used to indicate missing or bad values within the data set submitted. 10.2.2 Confidence Level/Accuracy Judgment The confidence level of this data set is high, since the submitted data have been visually checked for inconsistencies. Perhaps the greatest potential error is associated with the ground heat flux (Qg), which is obtained by residual. This same system has been used successfully in previous experiments at the Experimental Lakes Area, in northwest Ontario. 10.2.3 Measurement Error for Parameters Energy balance terms are thought to be within 10% when calculated, and certainly less than that when measured directly, the error in this case is discussed in Section 5.2.1. As discussed above, ground heat flux error could be larger since it is calculated by residual from all other energy budget terms. 10.2.4 Additional Quality Assessments Since the calculated surface energy budget and CO2 flux is based upon the calculation of an accurate momentum flux or eddy diffusivity value (K), a test was initiated toward the end of the campaign to test this calculated variable. In addition to the profile measurements of wind speed, a sonic anemometer was placed on the tower and the momentum coefficient was calculated using this instrument. Over the 4 days of overlapping measurement, differences between systems were not significant, and no corrections due to over- or underestimation were suggested. 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 See Section 10.1. 11.2 Known Problems with the Data There were no known problems with the submitted data. 11.3 Usage Guidance None required. 11.4 Other Relevant Information Beavers were frequently sighted, and seemed completely undisturbed by our tower in the center of their pond. In fact, they seemed quite inquisitive and were often seen passing near the tower platform. There was one bear sighting at the pond edge, even with the nearby noisy generator. Fauna environmental impact was therefore negligible. 12. Application of the Data Set These data are useful for the study of water, energy, and carbon exchange in a beaver pond. 13. Future Modifications and Plans None. 14. Software 14.1 Software Description None given. 14.2 Software Access None given. 15. Data Access 15.1 Contact for Data Center/Data Access Information These BOREAS data are available from the Earth Observing System Data and Information System (EOS-DIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory (865) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 15.2 Procedures for Obtaining Data BOREAS data may be obtained through the ORNL DAAC World Wide Web site at http://www-eosdis.ornl.gov/ or users may place requests for data by telephone, electronic mail, or fax. 15.3 Output Products and Availability Requested data can be provided electronically on the ORNL DAAC's anonymous FTP site or on various media including, CD-ROMs, 8-MM tapes, or diskettes. The complete set of BOREAS data CD-ROMs, entitled "Collected Data of the Boreal Ecosystem-Atmosphere Study", edited by Newcomer, J., et al., NASA, 1999, are also available. 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products These data are available on the BOREAS CD-ROM series. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Campbell Scientific Corporation CR7 Manual LI-COR 6252 Gas Analyzer Manual 17.2 Journal Articles and Study Reports Oke, T.R. 1987. Boundary layer climates. Routledge, Second Edition, New York, 435p. Roulet, N.T., N. Comer, A. Dove, J. Ecthevery, C. Robinson, S. Glenn, and P. Crill. (date unknown). Missing carbon sinks, beaver ponds, and the boreal carbon budget. Centre for Climate and Global Change Newsletter, 6(1): 5-8. Roulet, N.T., P.M. Crill, N.T. Comer, A.E. Dove, and R.A. Bourbonniere. 1997. CO2 and CH4 between a boreal beaver pond and the atmosphere. Journal of Geophysical Research. 102(D24). pp. 29,313-29,320. Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 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. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). 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.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 Reasearch. 102(D24):28,731-28,770. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms A/D - Analog to Digital ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System BVP - Beaver Pond CD-ROM - Compact Disk-Read-Only Memory DAAC - Distributed Active Archive Center DOC - Dissolved Organic Carbon EC - Eddy Covariance EOS - Earth Observing System EOSDIS - EOS Data and Information System GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center HTML - HyperText Markup Language IRGA - Infrared Gas Analyzer NAD83 - North American Datum of 1983 NASA - National Aeronautics and Space Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park PAR - Photosynthetically Active Radiation PC - Personal Computer PPFD - Photosynthetic Photon Flux Density REBS - Radiation Energy Balance Systems SSA - Southern Study Area TF - Tower Flux TGB - Trace Gas Biogeochemistry URL - Uniform Resource Locator WAB - Wind Aligned Blob WMO - World Meteorological Organization 20. Document Information 20.1 Document Revision Date Written: 22-May-1995 Revised: 25-May-1999 20.2 Document Review Date(s) BORIS Review: 08-Apr-1999 Science Review: 20.3 Document ID 20.4 Citation When using these data please acknowledge N. Roulet and his team. If using data from the BOREAS CD-ROMs please also reference the data as: Dr. N. T. Roulet, "The Fluxes of Energy and Trace Gases from Beaver Ponds and Dry upland Forest Floor in the NSA."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, A. Papagno, D. Rinker, R. Strub, T. Twine, F. Hall, and P. Sellers. CD-ROM. NASA, 1999. 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, A. Papagno, 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: TOWER FLUX BEAVER POND METEOROLOGY SENSIBLE HEAT FLUX LATENT HEAT FLUX CARBON DIOXIDE FLUX CARBON DIOXIDE CONCENTRATION PHOTOSYNTHETICALLY ACTIVE RADIATION PAR NET RADIATION AIR TEMPERATURE VAPOR PRESSURE WIND SPEED RAINFALL TGB04_NSA-BP_Flux.doc 06/09/99