BOREAS HYD-01 Under-Canopy Precipitation Data Summary Under-canopy precipitation measurements were made by the BOREAS HYD-01 science team in 1994, 1995, and 1996 at various flux tower sites in the NSA and SSA. In 1994, these data were collected at the NSA-OJP, NSA-YJP, SSA-OJP, and SSA-YJP sites. Starting in 1995 and ending in 1997, data were collected at the NSA-OBS, NSA-OJP, NSA-YJP, and SSA-OA. These data were collected to support HYD-01 research by measuring the amount of water that falls through the canopy and is intercepted by the ground or moss. These data coincide with volumetric soil moisture measurements made by HYD-01. 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-01 Under-Canopy Precipitation Data 1.2 Data Set Introduction Under canopy precipitation measurements were made by the BOReal Ecosystem- Atmosphere Study (BOREAS) Hydrology team number 1 (HYD-01) in 1994, 1995, and 1996 at various flux tower sites in the Northern Study Area (NSA) and the Southern Study Area (SSA). In 1994, these data were collected at the NSA-Old Jack Pine (OJP), NSA-Young Jack Pine (YJP), SSA-OJP, and SSA-YJP sites. Starting in 1995 and ending in 1997, data were collected at the NSA-Old Black Spruce (OBS), NSA-OJP, NSA-YJP, and SSA-Old Aspen (OA). 1.3 Objective/Purpose The objective of this study was to measure under-canopy precipitation at the flux towers where soil moisture was being measured. 1.4 Summary of Parameters Under-Canopy Precipitation 1.5 Discussion Under-canopy precipitation was used to close the local hydrologic balance in the vicinity of the soil profiles. By placing an under-canopy rain gauge device in the vicinity of each soil moisture profile, ideally, the volumetric soil moisture increase in the profile should equal the applied precipitation measured by the rain gauge. This provides an important check for the soil moisture measurements. Additionally, the under-canopy precipitation can be used to estimate canopy interception by comparing to gauges mounted above the canopy on the towers. 1.6 Related Data Sets BOREAS HYD-01 Volumetric Soil Moisture Data BOREAS HYD-01 Soil Hydraulic Properties BOREAS HYD-06 Moss/Humus Moisture Data BOREAS HYD-06 Ground Measurements of Soil Moisture BOREAS HYD-06 Aircraft Gamma Ray Soil Moisture Data 2. Investigator(s) 2.1 Investigator(s) Name and Title Richard H. Cuenca, Professor Department of Bioresource Engineering Oregon State University 2.2 Title of Investigation Coupled Atmosphere-Forest Canopy-Soil Profile Monitoring and Simulation 2.3 Contact Information Contact 1 ------------ Richard H. Cuenca, Professor Oregon State University Corvallis, OR (541) 737-6307 (541) 737-2082 (fax) cuencarh@pandora.bre.orst.edu Contact 2 ------------ For questions regarding 1995, 1996, and 1997 data collection: Shaun F. Kelly, Research Assistant Oregon State University Corvallis, OR (541) 737-6314 (541) 737-2082 (fax) kellys@engr.orst.edu Contact 3 ------------ For questions regarding 1994 data collection: David Stangel Oregon State University Corvallis, Oregon (503) 737-6314 (503) 737-2082 (fax) stangel@pandora.bre.orst.edu Contact 4 ------------ David Knapp Raytheon ITSS NASA GSFC Greenbelt, MD (301) 286-1424 (301) 286-0239 (fax) David.Knapp@gsfc.nasa.gov 3. Theory of Measurements These measurements of under-canopy precipitation were made to determine the amount of precipitation that hit the soil, below a forested canopy. These measurements are useful in determining the amount of water that went into the soil, increasing the volumetric soil moisture. 4. Equipment 4.1 Sensor/Instrument Description 4.1.1 Collection Environment The wedge-shaped rain gauge is inserted into a bracket that is supplied with the gauge. The bracket is mounted on a short wood stake that has been driven into the ground a few inches. To read the gauge, water levels are recorded within the gauge with the highest accuracy possible for the corresponding water level. After each reading, the gauge is removed from the bracket and emptied of its contents. Tipping bucket rain gauges were mounted on a 0.5-in. diameter metal pipe (3 ft long) inserted into the ground. The tipping bucket was secured to the pipe using hose clamps at a height of 0.5 m (from funnel lip). The tipping bucket was leveled and debris cleaned from the screen during site visits. Under-canopy rain gauges were located in the vicinity of soil moisture measurement profiles. 4.1.2 Source/Platform The rain gauge is mounted on a wooden stake. 4.1.3 Source/Platform Mission Objectives The wooden stake is used to hold the rain gauge. 4.1.4 Key Variables Under canopy precipitation 4.1.5 Principles of Operation Rain Gauge The wedge-shaped rain gauge is mounted on a stake at ground level. It can measure up to 150 cm of water and the accuracy decreases as more water accumulates in the gauge. Measurement line density varies from +/- 0.1 cm at the bottom to +/- 2.5 cm at the top. The tipping bucket rain gauge is a smaller adaptation of the standard Weather Bureau tipping bucket rain gauge. It measures precipitation at rates up to 2 in. per hour with an accuracy of +/-1%. Output is a switch closure for each bucket tip. A tip occurs with each 0.1 mm of precipitation. In 1994, the rain gauges were read every other day during the Intensive Field Campaigns (IFCs) corresponding to a neutron probe water content measurement. All water contents are for the time interval between the date of the measurement and the last recorded precipitation event. The rain gauges were located at the OJP and YJP sites in both the NSA and the SSA. The rain gauges were installed less than 2 feet from the neutron probe access tubes. In general terms the gauges were located between 50 and 150 meters in a northeasterly direction out from the flux tower. 4.1.6 Sensor/Instrument Measurement Geometry Not applicable 4.1.7 Manufacturer of Sensor/Instrument Wedge-shaped Rain Gauges: Tru-Check Edwards Mfg.Co Box 166 Albert Lea, MN 56007 (507) 373-8206 Tipping Bucket Rain Gauges: Texas Electronics P.O. Box 7225, Inwood-Station Dallas, TX 75209 (214) 631-2490 4.2 Calibration 4.2.1 Specifications Wedge-shaped Rain Gauges: None given. TE525 Tipping Bucket Rain Gauge Range of Indication: Infinite, in increments of 0.1 mm Accuracy: 1.0% at 2 inch/hr or less Signal Output: Momentary switch closure approximately 135 ms Environmental Limits: Temperature: 0 to 50 °C Humidity: 0 – 100% Physical Data: Diameter: 6.25 in. overall Height: 12 in. Weight: 2.5 lbs. Receiving Orifice: Gold anodized spun aluminum knife-edge collector ring and funnel assembly Ring Diameter: 9.664 in. Resolution: 0.1 mm Calibration: 16.00 fluid oz. (100 bucket tips) Mounting: Side bracket with clamps mounted to pole Material: Aluminum Cable: 2-conductor standard shielded cable 4.2.1.1 Tolerance None given. 4.2.2 Frequency of Calibration The wedge rain gauge was not field calibrated. TE525 Tipping Bucket Rain Gauge Calibration/Cleaning Frequency: Sensor is factory calibrated and does not require field calibration. Debris filters, funnel orifices, and bucket reservoirs were cleaned during site inspections. 4.2.3 Other Calibration Information None. 5. Data Acquisition Methods The data were acquired by reading the wedge-shaped rain gauges (1994) on a regular bassis, when soil moisture was measured. After the 1994 data collection, the data were read from the tipping bucket rain gauges. 6. Observations 6.1 Data Notes Some clogging occurred during the measurement periods at long-term measurement sites, which allowed water to pool in the funnel. 6.2 Field Notes None. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage Multiple in situ measurements were made in the vicinity of the flux towers for each respective site. In 1994, these data were collected at the OJP and YJP sites in the NSA and SSA. After 1994, they were collected at the OBS, OJP, and YJP sites in the NSA and at the OA in the SSA. The North American Datum 1983 (NAD83) coordinates of the sites are: SITE LONGITUDE LATITUDE ------------------ ------------- ------------- NSA-OJP 98.62396° W 55.92842° N NSA-YJP 98.28706° W 55.89575° N NSA-OBS 98.48139° W 55.88007° N SSA-OA 106.19779° W 53.62890° N SSA-OJP 104.69203° W 53.91634° N SSA-YJP 104.64529° W 53.87581° N 7.1.2 Spatial Coverage Map The following maps were provided showing the sites where measurements were made in 1996. 1996 Measurements at NSA OJP 1996 Measurements at NSA YJP 7.1.3 Spatial Resolution These data represent point measurements at the designated sites. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The periods over which data were collected at each site varied. The overall period of data collection was from 23-MAY-1994 to 24-JUN-1997. 7.2.2 Temporal Coverage Map Data Collection Site Start End______ NSA-OJP 15-Jun-1994 15-Sep-1994 NSA-YJP 31-May-1994 15-Sep-1994 SSA-OJP 23-May-1994 06-Sep-1994 SSA-YJP 23-May-1994 06-Sep-1994 After 1994 Data Collection Site Start End______ NSA-OJP 25-Jun-1996 06-Nov-1996 NSA-YJP 27-Jun-1996 06-Nov-1996 NSA-OBS 14-Jul-1995 24-Jun-1997 SSA-OA 17-Jun-1996 02-Nov-1996 7.2.3 Temporal Resolution In 1994, the measurements were made every other day during the field campaigns, corresponding to soil moisture measurements. After 1994, with the automated equipment in place, measurements were taken every hour while precipitation events were occurring. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (h01uncpd.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (h01uncpd.def). 8. Data Organization 8.1 Data Granularity Data for 1994 is in one file and data for 1995-1997 is in a second. 8.2 Data Format(s) The data files contain 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 (h01uncpd.def). 9. Data Manipulations 9.1 Formulae 9.1.1 Derivation Techniques and Algorithms The amount of precipitation is read directly from the wedge-shaped gauge. For the tipping bucket gauges, the amount of precipitation is determined from the number of tips (see Section 4.2.1). 9.2 Data Processing Sequence 9.2.1 Processing Steps The BOREAS Information System (BORIS) staff processed the data by: 1) Reviewing the initial data files and loading them on-line 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 HYD-01 team to document the data set 5) Extracting the standardized data into logical files 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None given. 9.3.2 Calculated Variables None given. 9.4 Graphs and Plots None given. 10. Errors 10.1 Sources of Error Wedge Rain Gauge The device is so simple that errors were reduced to leaves falling in the gauges or a gauge being tipped over. The high frequency of data collection ensured that evaporation from the gauges was a minor factor in the readings. The only major limitation is simply the accuracy in which one can read the level of water within the gauge. Tipping Bucket Rain Gauge Unattended automated tipping bucket devices did not function in the winter during freezing conditions. Spring and fall readings may indicate collected snow and subsequent melting in the funnel. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgment Unattended tipping bucket rain gauges used from 1995-97 were periodically cleaned, yet they almost all invariably included debris that collected in the screen, and some were completely clogged. For this reason, at most sites a minimum of two gauges were installed. Rarely were both gauges clogged. Questionable data may be noted when large differences exist between gauges. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center The data that were received from HYD-01 were loaded into the relational data base and checked to make sure that no errors were introduced in loading the data. 11. Notes 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data None given. 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set This data set can be used with the volumetric soil moisture data to determine how soil moisture changes with time during rain events and during dry periods. These under-canopy precipitation data indicate how much precipitation falls on the soil. These data can be used in various kinds of hydrological and ecological models. 13. Future Modifications and Plans None given. 14. Software 14.1 Software Description None given. 14.2 Software Access None given. 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 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or FAX. 15.4 Data Center Status/Plans The HYD-01 under-canopy precipitation data are available from the EOSDIS ORNL DAAC (Earth Observing System Data and Information System) (Oak Ridge National Laboratory) (Distributed Active Archive Center). The BOREAS contact at ORNL is: 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 Tabular ASCII files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation None given. 17.2 Journal Articles and Study Reports Cuenca, R.H., D.E. Stangel, and S.F. Kelly. 1997. Soil water balance in a boreal forest. Journal of Geophysical Research 102(D24): 29355-29365. 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, 102 (D24): 28,731-28,770. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System CD-ROM - Compact Disk - Read Only Memory DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System GSFC - Goddard Space Flight Center HYD - Hydrology IFC - Intensive Field Campaign NASA - National Aeronautics and Space Administration NSA - Northern Study Area OA - Old Aspen OBS - Old Black Spruce OJP - Old Jack Pine ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park SSA - Southern Study Area TE - Terrestrial Ecology URL - Uniform Resource Locator YA - Young Aspen YJP - Young Jack Pine 20. Document Information 20.1 Document Revision Dates Written: 23-Apr-1997 Last Updated: 07-Dec-1998 20.2 Document Review Dates BORIS Review: 27-Nov-1998 Science Review: 24-Nov-1998 20.3 Document ID 20.4 Citation Please contact Dr. Richard Cuenca before publishing results based on this data set. 20.5 Document Curator 20.6 Document URL Keywords Under-canopy Precipitation Soil moisture HYD01_UNCP.doc 01/13/99