BOREAS HYD-08 Throughfall Data Summary The BOREAS HYD-08 team made measurements of surface hydrological processes at the SSA (1996) and NSA OBS (1994) Tower Flux sites, supporting its research into point hydrological processes and the spatial variation of these processes. These data were collected during the 1994 and 1996 field campaigns. Data collected may be useful in characterizing canopy interception, drip, throughfall, moss interception, drainage, evaporation, and capacity during the growing season at daily temporal resolution. This particular data set contains the measurements of throughfall, which is the amount of precipitation that fell through the canopy. A nested spatial sampling plan was implemented to determine spatial variations of the measured hydrological processes and ultimately the impact of these variations on modeled carbon and water budgets. These data are stored in ASCII text 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 HYD-08 Throughfall Data 1.2 Data Set Introduction The BOReal Ecosystem-Atmosphere Study Hydrology (HYD)-08 team made measurements of surface hydrological processes at the Southern Study Area (SSA) (1996) and Northern Study Area (NSA) Old Black Spruce (OBS) (1994) Tower Flux sites, supporting its research into point hydrological processes and the spatial variation of these processes. These data were collected during the 1994 and 1996 field campaigns. Data collected may be useful in characterizing canopy interception, drip, throughfall, moss interception, drainage, evaporation, and capacity during the growing season at daily temporal resolution. This particular data set contains the measurements of throughfall, which is the amount of precipitation that fell through the canopy. A nested spatial sampling plan was implemented to determine spatial variations of the measured hydrological processes and ultimately the impact of these variations on modeled carbon and water budgets. These data are stored in American Standard Code for Information Interchange (ASCII) text files. 1.3 Objective/Purpose The objective of these data sets was to quantify the magnitude and spatial variation of storages and fluxes of water at the moss surface and during precipitation events in selected Picea Mariana stands. The following parameters were measured to permit future parameterization of flux models: throughfall, stemflow, moss water storage, and gross precipitation. A nested spatial sampling plan was implemented to characterize the length scales of variations of the measured parameters for future use in modeling studies and for comparison with measurements at the black spruce flux towers located in the study sites, SSA-OBS and NSA-OBS. 1.4 Summary of Parameters Precipitation that has fallen through the canopy (after storm events) 1.5 Discussion Hydrological processes such as canopy evaporation and moss storage and evaporation may play a significant role in controlling water fluxes during the growing season in boreal wetlands. Canopy interception and moss storages and evaporation were measured using mass balance methods (throughfall catch buckets and lysimeters) to give a quantitative estimate of these processes for sparse black spruce stands. More importantly, the spatial sampling scheme allowed quantification of the expected variation of these processes within the footprint of a colocated flux measurement tower. This will allow consideration of the sub-tower-footprint controls on vapor fluxes that the tower is measuring. In addition, these data sets will be useful in parameterizing flux models for the site targeted as well as determining the typical variation in fine scale processes that the models may have to account for when scaling to watershed and regional extents. 1.6 Related Data Sets BOREAS HYD-08 1996 Gravimetric Moss Moisture Data BOREAS HYD-08 1994 Gravimetric Moss Moisture Data BOREAS HYD-08 Gross Precipitation Data 2. Investigator(s) 2.1 Investigator(s) Name and Title Dr. Lawrence Band University of Toronto Department of Geography Toronto, Ontario 2.2 Title of Investigation Simulation of Boreal Ecosystem Carbon and Water Budgets: Scaling from Local to Regional Extents 2.3 Contact Information Contact 1 --------- Richard Fernandes University of Toronto Department of Geography Toronto, Ontario (416) 978-5070 (416) 978-6729 (fax) fernande@geog.utoronto.ca Contact 2 ------------ Xuewen Wang University of Toronto Department of Geography Toronto, Ontario (416) 978-5070 (416) 978-6729 (fax) wangx@geog.utoronto.ca Contact 3 --------- David Knapp Raytheon STX Corporation NASA GSFC Greenbelt, MD (301) 286-1424 (301) 286-0239 (fax) David.Knapp@gsfc.nasa.gov 3. Theory of Measurements Throughfall is the amount of precipitation that falls through a tree canopy. Throughfall catch buckets were placed at random locations and beside each turf lysimeter in each nested sampling plot. In addition, four intensive throughfall plots were located with only throughfall catch buckets. In all plots, the catch buckets were placed so that the lip of the bucket was just above the level of the live moss layer. Throughfall was measured using the same protocol that was used for gross precipitation, with care taken to extract any litter in the buckets. 4. Equipment 4.1 Sensor/Instrument Description Throughfall Catch Buckets Clear plastic buckets with an 11 cm diameter orifice, 10 cm diameter base, and 10 cm depth were used. 4.1.1 Collection Environment None given. 4.1.2 Source/Platform Throughfall Gauges - Placed in the live moss surface layer flush with the live moss surface. 4.1.3 Source/Platform Mission Objectives The objective was to measure daily changes in water storages or turf weights. 4.1.4 Key Variables Throughfall Gauge - Throughfall (the amount of precipitation that falls through the forest canopy to the ground.) 4.1.5 Principles of Operation The gauges were designed to hold an amount of water that fell through the canopy, that was weighed. The weights were used to determine the water equivalent depth. 4.1.6 Sensor/Instrument Measurement Geometry All throughfall gauges were repositioned using a bubble level to ensure that they were upright. 4.1.7 Manufacturer of Sensor/Instrument Gauges - Darryl Carlysle Moses and Kira Dunham (University of Toronto, Dept. of Geography) Weigh Scales - (2) MARS MS3000W Series 4.2 Calibration The weigh scales were calibrated to within the manufacturer's specifications immediately before the measurement campaign and at the University of Toronto after the campaign. The effect of the weigh scales being off level were also tested, with no appreciable difference for tilt angles less than 20 degrees (which were defined by the first indent in the bubble level gauge used in the field). 4.2.1 Specifications Weight Scales Weight < 1 kg: accurate to +/- 0.1 g Weight > 1 kg: accurate to +/- 1.0 g 4.2.1.1 Tolerance None given. 4.2.2 Frequency of Calibration The weigh scales were calibrated to within the manufacturer's specifications immediately before the measurement campaign and at the University of Toronto after the campaign. 4.2.3 Other Calibration Information None. 5. Data Acquisition Methods Each gauge and lysimeter was placed at a randomly selected location in each stratified plot or in clearings in the case of throughfall gauges. The locations were not changed during the field campaign. Measurements were made at each plot for all gauges and lysimeters before moving to another plot. The measurements were made by weighing the amount of water in the gauge. These weights were converted to water depths based on the orifice area of the gauge. 6. Observations 6.1 Data Notes None given. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics All 1996 measurement plots were located within 500 m of the SSA-OBS flux tower along a single transect leading radially outwards from the tower. The goal was to place the plots on a perceived wetness gradient while keeping them within the flux tower footprint. In addition, each plot was located so that it was separated from the others to characterize the typical spatial variability of surface hydrological processes. Unfortunately, no plot was located in a region dominated by Sphagnum bogs, so turf lysimeters with sphagnum were located in isolated sphagnum patches within 10 m of each plot. The 1994 throughfall data were collected near Joey Lake and near the NSA-OBS tower. 7.1.1 Spatial Coverage In 1996, seven plots were located along a transect in the vicinity of the SSA- OBS flux tower. The locations of the plot and of the actual measurements are given in the following figures. Each plot had five live turf lysimeters and five throughfall gauges (one throughfall gauge near each live turf lysimeter). In addition, two throughfall plots with over 20 throughfall gauges were located independently. At the Joey Lake site in 1994, these data were collected at four different plots. At the NSA-OBS site in 1994, the data were taken from two plots located near the flux tower. The plots were about 30 meters apart, about 10 m by 10 m square each. The samples within each plot were about 5 meters apart. The approximate locations of the various plots are as follows: BOREAS Grid Site Longitude Latitude X Y_____ NSA (Joey Lake) 98.15026W 55.46676N 807.025 571.969 NSA-OBS (Flux Twr.) 98.48139W 55.88007N 778.216 613.516 SSA-OBS (Flux Twr.) 105.11779W 53.98717N 385.012 348.646 7.1.2 Spatial Coverage Map None. 7.1.3 Spatial Resolution Each measurement site is located on the figures above. Each throughfall gauge had an 11 cm diameter orifice, 10 cm diameter base, and 10 cm depth. The throughfall gauges may catch precipitation from a region larger than their orifices. The "fetch" of a throughfall or rain gauge depends on wind speed, precipitation intensity, and the cover over the gauge. 7.1.4 Projection These plots are at point locations. A map projection is not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The data at the SSA-OBS were collected from July to August 1996 with some small gaps. The data at the NSA-OBS were collected from 23-Aug-1994 to 15-Sep-1994 with some gaps. The data at Joey Lake (near NSA) were collected from 24-Jun-1994 to 06-Sep-1994 with some gaps. 7.2.2 Temporal Coverage Map None. 7.2.3 Temporal Resolution In 1996, data were collected daily and after each rain event, where possible. After the time was recorded, data collection proceeded for 1.5 to 2 hours, in order to visit all of the gauges. Therefore, the actual data collection time is accurate to within 1.5 to 2.0 hours. The amount of precipitation recorded is the amount that fell since the gauge was last checked. The temporal resolution of the 1994 data is assumed to be similar to that of the 1996 data. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (h8thrfld.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (h8thrfld.def). 8. Data Organization 8.1 Data Granularity All of the BOREAS HYD-08 Throughfall Data are contained in one dataset. 8.2 Data Format(s) A data record consists of a series of numerical and character fields of American Standard Code for Information Interchange (ASCII) characters of varying length. The fields are separated by commas with the character fields enclosed in single apostrophe marks. Sample data records are shown in the companion data definition file (h8thrfld.def). 9. Data Manipulations 9.1 Formulae See Section 9.1.1. 9.1.1 Derivation Techniques and Algorithms The computation of water equivalent depth for throughfall gauges was performed using: d (mm) = 1000 (mm/m) * mass_water(g) / ( 1000kg/m3 * area_gauge_bottom(m2) ) 9.2 Data Processing Sequence 9.2.1 Processing Steps 1. Set up necessary equipment. 2. Performed daily weighings and emptied weighed gauges. 3. Performed the necessary data manipulations. 4. Added the necessary column headings. 5. Transferred the information to the BOREAS Information System (BORIS). 6. BORIS staff loaded the data into the relational data base. 9.2.2 Processing Changes None given. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None. 9.3.2 Calculated Variables See Section 9.1.1. 9.4 Graphs and Plots None given. 10. Errors 10.1 Sources of Error Quantifiable Errors 1. Location errors - The plots were located with reference to the flux tower using dead reckoning. Errors on the order of +/-10 m can be expected for Figure 1 (location of plot origins) and +/- 0.1 m for Figure 2 (location of measurement sites within plots). 2. Dimensional measurements - Measurements of radii, length, and width dimensions were made using a metric hand ruler. An error of +/-0.5 mm in precision is possible. This will result in negligible errors in computed surface areas of catch gauges or turf trays. 3. Throughfall gauge weighing error - Tests were performed to detect the weight of water drops present on the sides of throughfall gauges. These weights were not measurable. The average weight of all throughfall gauges was used to compute the net weight of water in the gauge. The error in using the average weight is less than +/- 0.1 g and can be considered negligible. 4. Weigh scale errors - The weigh scale errors assuming no contamination of the weighing surface (e.g., water drops on it) are given by the manufacturer as a precision error of +/- 0.1 g for weights less than 1,000 g and +/- 1.0 g for weights greater than 1,000 g. Unquantifiable Errors Throughfall Gauges - Splashing of drops outside the gauge. This error suggests a negative accuracy error for throughfall gauges. However, given that splash is larger for larger storms (the water level in the container is higher and the drop size and velocity is likely higher) the accuracy bias should be small relative to the measured value. - Lack of leveling because of wind or animal disturbance. Gauges that were substantially tilted were recorded but flagged and have not been included in the submitted data set. - Drip not completed at observation time. It is possible that the drip process had not completed after the observation, especially for nighttime rains. No attempt was made to reconcile this possible negative accuracy error; however, substantial drip would be recorded in the subsequent measurement. Gross Precipitation Gauges - Errors caused by wind turbulence around the gauge, evaporation from the collector funnel or condensation on the funnel are possible. It is likely that precipitation is underestimated because of evaporation from the funnel. 10.2 Quality Assessment 10.2.1 Data Validation by Source These data are very preliminary. General trends in the data are reliable; however, individual measurements may be completely in error. 10.2.2 Confidence Level/Accuracy Judgment Mean values or plots and gross precipitation accuracy is estimated to be approximately 2 out of 5, individual measurements at 1 out of 5. 10.2.3 Measurement Error for Parameters Estimates of errors of each measurement variable are given below. Time: +/- 2 hours Throughfall: The accuracy of the throughfall measurements is thought to be approximately 5%. The precision of each measurement is directly related to the precision of the scale that weighed the gauge. 10.2.4 Additional Quality Assessments Data quality assessment is ongoing by the investigator. 10.2.5 Data Verification by Data Center The data were loaded into the relational data base and checked to ensure that the values were loaded correctly. 11. Notes 11.1 Limitations of the Data Isolated data points may be in complete error because of improper recording or reformatting during documentation. Revision of data is continuing. 11.2 Known Problems with the Data None given. 11.3 Usage Guidance Moss water fluxes are conservative; any strong jumps in time series should be flagged as potential measurement or recording errors unless explained by commensurate inputs. 11.4 Other Relevant Information None. 12. Application of the Data Set The HYD-08 data sets can be used for: 1. Quantifying rough canopy interception rates for given storm size at the SSA- OBS site. 2. Quantifying daily moisture fluxes in moss layers. 3. Possibly inferring relationships between stand parameters and measured fluxes. 4. Parameterizing flux models (especially hydrological models at stand to local scale). 13. Future Modifications and Plans Data quality assessment is continuing by the investigators. 14. Software 14.1 Software Description Not applicable. 14.2 Software Access Not applicable. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) Elizabeth.Nelson@gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, fax, or electronic mail. 15.4 Data Center Status/Plans The HYD-08 throughfall data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory Oak Ridge, TN (423) 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 ASCII data files. 17. References None given. 17.1 Platform/Sensor/Instrument/Data Processing Documentation None. 17.2 Journal Articles and Study Reports Haddeland, I. and D.P. Lettenmaier. 1995. Hydrologic Modeling of Boreal Forest Ecosystems. Water Resources Series Technical Report No. 143. University of Washington, 123 pp. Price, A.G., K. Dunham, T. Carleton, and L.E. Band. 1997. Variability of water fluxes through the Black Spruce (Picea Mariana) canopy and Feather Moss (Pleurozium Schreberi) carpet in the Boreal Forest of Northern Manitoba. Journal of Hydrology, 196, 310-323. 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 Research, BOREAS Special Issue, 102(D24), Dec. 1997, pp. 28731-28770. 17.3 Archive/DBMS Usage Documentation None given. 18. Glossary of Terms None given. 19. List of Acronyms ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System CD-ROM - Compact Disk (optical), Read-Only Memory DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FFC-T - Focused Field Campaign - Thaw GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center HYD - Hydrology IFC - Intensive Field Campaign NASA - National Aeronautics and Space Administration NSA - Northern Study Area OBS - Old Black Spruce ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park SSA - Southern Study Area URL - Uniform Resource Locator 20. Document Information 20.1 Document Revision Date Written: 20-Nov-1996 Updated: 04-Aug-1998 20.2 Document Review Date(s) BORIS Review: 24-Jul-1998 Science Review: 20.3 Document ID 20.4 Citation This data product was collected and processed by the BOREAS Science Team HYD-08, led by Prof. Lawrence Band at the University of Toronto. Please contact the principal investigator, Dr. Lawrence Band, before publishing results that are based on these data. 20.5 Document Curator 20.6 Document URL KEYWORDS PRECIPITATION MOSS HYD08_Throughfall.doc 08/20/98