BOREAS HYD-03 Subcanopy Incoming Solar Radiation Measurements Summary The BOREAS HYD-03 team collected several data sets related to the hydrology of forested areas. This data set contains solar radiation measurements from several pyranometers (solar radiometers) placed on the snow surface in jack pine (1994) and black spruce and aspen forests (1996). An array of radiometers was used to collect data for 3-4 consecutive days in each forest type to study the hypothesis that energy transfer and snow water equivalent would vary spatially as a function of canopy closure. The quality of the data is good, because the days were generally clear and the radiometers were checked daily to remove anything that landed on the radiometers. 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 HYD-03 Subcanopy Incoming Solar Radiation Measurements 1.2 Data Set Introduction This data set contains solar radiation measurements from several pyranometers (solar radiometers) placed on the snow surface in jack pine (1994) and black spruce and aspen forests (1996). In each forest, data were collected for 3 to 4 days. 1.3 Objective/Purpose This study was undertaken to predict spatial distributions of energy transfer and snow properties important to the hydrology, remote sensing signatures, transmissivity of gases through the snow and their relation to forests in boreal ecosystems. This data set provides a measure of the variability of incoming solar radiation on the snow surface in the various forests. These data will aid in validating a radiative transfer model that predicts the radiation environment beneath a discontinuous forest canopy. The model output will be used to assist in predicting the timing of snow melt in the forest. 1.4 Summary of Parameters Parameters measured with respect to this documentation are subcanopy incoming solar radiation. 1.5 Discussion This study was conducted under the hypothesis that energy transfer and snow water equivalent would vary spatially as a function of canopy closure. Net solar radiation has been long known as the primary driving force in snow melt models, yet this parameter is difficult to quantify at the forest floor because of the high spatial variability in radiation transmission through the discontinuous canopy. For this reason, an attempt was made to quantify that variability by operating several (9 in 1994 and 10 in 1996) pyranometers. These pyranometers were run over 3 days of clear sky conditions in 1994 and 4 days in 1996. The quality of the data is good, because the days were generally clear and the radiometers were checked daily (except in the Boreal Ecosystem-Atmosphere Study Southern Study Area (SSA) Old Aspen (OA) in 1996). Any snow that landed on the radiometers was brushed clear, and data for the period were deleted. 1.6 Related Data Sets BOREAS TF-02 SSA-OA Tower Flux Data BOREAS TF-01 SSA-OA Tower Flux Data BOREAS TF-05 SSA-OJP Tower Flux Data BOREAS TF-09 SSA-OBS Tower Flux Data BOREAS HYD-03 Subcanopy Meteorological Measurements 2. Investigator(s) 2.1 Investigator(s) Name and Title Robert E. Davis Research Physical Scientist U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) 2.2 Title of Investigation Distributed Energy Transfer Modeling in Snow and Soil for Boreal Ecosystems 2.3 Contact Information Contact 1 ------------- Janet P. Hardy U.S. Army CRREL Hanover, NH (603) 646-4306 jhardy@crrel.usace.army.mil Contact 2 ------------- Robert E. Davis U.S. Army CRREL Hanover, NH (603) 646-4219 bert@crrel.usace.army.mil Contact 3 ------------- David Knapp NASA GSFC Greenbelt, MD (301) 286-1424 David.Knapp@gsfc.nasa.gov 3. Theory of Measurements In 1994, nine random measurements of incoming solar radiation were made at the snow surface at the SSA-Old Jack Pine (OJP) site to assess the variability in radiation caused by the forest structure. The pyranometers were randomly placed; some measurements were made directly adjacent to tree stems, some in small canopy gaps. These measurements took place over a period of 3 days, and each day, the pyranometers were randomly relocated. In 1996, 10 random measurements of incoming solar radiation were made at the snow surface at SSA-Old Black Spruce (OBS) and SSA-OA to assess the variability in radiation caused by the forest structure. The pyranometers were randomly placed; some measurements were made directly adjacent to tree stems, some in small canopy gaps. These measurements took place over a period of 4 days, and each day the pyranometers were randomly relocated, except in SSA-OA. 4. Equipment: 4.1 Sensor/Instrument Description Eppley Precision Spectral Pyranometer, measuring wavelengths between approximately 285 and 2,800 nm. This instrument is believed to be the most accurate radiometer produced commercially for the measurement of Sun and sky radiation. The pyranometer comprises a circular multijunction thermopile that is temperature compensated to operate effectively at temperatures of -50°C. 4.1.1 Collection Environment In all cases, data were collected during the winter, most often during a clear sky period with the lowest air temperatures above the operating threshold of -50°C. During the 1996 measurement in SSA-OBS, light snowfall landed on the radiometers. The radiometers were brushed clear of snow, and data collected while they were snow covered were deleted. 4.1.2 Source/Platform Ground. 4.1.3 Source/Platform Mission Objectives The mission objective was to measure the variability of incoming solar radiation on the snow surface in SSA-OJP (1994) and SSA-OBS and SSA-OA (1996). 4.1.4 Key Variables Total (direct and diffuse) solar radiation beneath the forest canopy. Horizontal wind speed at 2 meters above ground beneath the forest canopy. Wind speed magnitude vector at 2 meters above ground beneath the forest canopy. Wind direction at 2 meters above ground beneath the forest canopy. Standard deviation of wind direction. Thermal radiation down. Canopy temperature. Trunk temperature. Air temperature at 2 meters above ground. Snow surface temperature. 4.1.5 Principles of Operation The pyranometer outputs a voltage proportional to the incoming radiation; the signal is monitored and data are processed on a Campbell Scientific datalogger (CR10). In 1994, measurements were made once every minute and averaged to give a 10-minute output. In 1996, measurements were made every 10 seconds and averaged to give 1-minute output. 4.1.6 Sensor/Instrument Measurement Geometry Sensors were located on the snow surface using either a foam block (1994) or the radiometer case (1996) for support on the snow surface. Sensors were leveled daily using the bubble level mounted on the radiometer base. 4.1.7 Manufacturer of Sensor/Instrument Eppley Laboratory, Inc. 12 Sheffield Ave. Newport, RI 02840 (401) 847-1020 4.2 Calibration All pyranometers were new in 1994 and were therefore factory calibrated, with reference to Eppley primary standards, just prior to deployment in the field in 1994. 4.2.1 Specifications Pyranometers Sensitivity: 9 microvolts per Watt per square meter. Receiver: circular 1 cm2 in area. Linearity: +/- 0.5% from 0 to 2,800 Watts per square meter. Cosine: +/- 1% from normalization 0-70° zenith angle +/- 3% from normalization 70-80° zenith angle 4.2.1.1 Tolerance see Section 4.2.1, Specifications. 4.2.2 Frequency of Calibration The manufacturer of the pyranometers recommends calibration after a cumulative use of 2 years. These radiometers were new at the beginning of the Focused Field Campaign-Winter (FFC-W) 1994 and therefore are well within calibration. Because they have been used for only ~20 days per year and stored in their dark case when not in use, the calibration should be valid for several years at the current rate of usage. 4.2.3 Other Calibration Information Available from the manufacturer. 5. Data Acquisition Methods Each pyranometer was placed on a styrofoam block (1994) or its carrying case (1996) and randomly set on the snow surface. Because of the random placement, some pyranometers were in forest gaps and others were adjacent to tree stems. Data were recorded on a Campbell Scientific datalogger. In 1994, the datalogger was programmed to measure incoming solar radiation every minute and output 10- minute averages. In 1996, the datalogger was programmed to measure incoming solar radiation every 10 seconds and output 1-minute averages. 6. Observations 6.1 Data Notes None given. 6.2 Field Notes 1994 Field Campaign Radiometers were randomly relocated at the following times: 08-Feb-1994 between 1700 and 1730 Greenwich Mean Time (GMT). 09-Feb-1994 between 1930 and 2000 GMT. 10-Feb-1994 radiometers removed around 1800 GMT. 1996 Field Campaign Radiometers were randomly relocated at the following times: 28-Feb-1996 between 2230 and 2245 GMT. 29-Feb-1996 between 2230 and 2242 GMT. 01-Mar-1996 between 2229 and 2246 GMT. 02-Mar-1996 between 2230 and 2239 GMT. 01-Mar-1996 at 1802 GMT: the radiometers were cleared of a thin dusting of snow (1802 begins good data). 03-Mar-1996 at 1730-1736 GMT: the radiometers were cleared of a thin snow cover. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage 1994: SSA-OJP (within 50 meters of tower). 1996: SSA-OBS (within 50 meters of tower). 1996: SSA-OA (within 50 meters of tower). Tower locations Tower Longitude Latitude --------------------------------- SSA-OJP 104.69203W 53.91634N SSA-OBS 105.11779W 53.98718N SSA-OA 106.19779W 53.6289N 7.1.2 Spatial Coverage Map None given. 7.1.3 Spatial Resolution The radiometers covered an area approximately 10 m x 10 m. 7.1.4 Projection Not applicable. 7.1.5 Grid Description None. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage FFC-W 1994: 06-10 Feb-1994 FFC-W 1996: 28-Feb-1994 - 08-Mar-1996 7.2.2 Temporal Coverage Map SSA-OJP: 06-10-Feb-1994 SSA-OBS: 28-03-Mar-1996 SSA-OA: 04-08-Mar-1996 7.2.3 Temporal Resolution 1994: 10-minute averages 1996: 1-minute averages 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (h03scrdd.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (h03scrdd.def). 8. Data Organization 8.1 Data Granularity All of the Subcanopy Incoming Solar Radiation Measurement Data are contained in one dataset. 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 a single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition files (h03scrdd.def). 9. Data Manipulations 9.1 Formulae Not applicable. 9.1.1 Derivation Techniques and Algorithms Not applicable. 9.2 Data Processing Sequence Not applicable. 9.2.1 Processing Steps Not applicable. 9.2.2 Processing Changes Not applicable. 9.3 Calculations 9.3.1 Special Corrections/Adjustments Not applicable. 9.3.2 Calculated Variables Not applicable. 9.4 Graphs and Plots Three plots are included in this documentation showing the variation in the measured data for the 3 or 4 day period at each site. For example, the plot of SSA-OBS solar radiation data shows the data for incoming radiation for all 10 pyranometers for the 4 day period, yielding 40 lines. The time of day on these plots is given in local time. 10. Errors 10.1 Sources of Error Assuming an operative instrument (each pyranometer was calibrated prior to use in the field), the sources of error include: a pyranometer that is covered by snow and the pyranometers losing their leveled orientation because of snow settling beneath the support boxes (pyranometers were releveled daily after being relocated). 10.2 Quality Assessment 10.2.1 Data Validation by Source Data were plotted and qualitatively compared to incoming solar radiation data obtained from above the canopy at SSA-OJP and SSA-OBS. Additionally, data collected during the time the radiometers were shuffled (see section 6.2, Field Notes) were removed. 10.2.2 Confidence Level/Accuracy Judgment Great care was taken to level the pyranometers during installation. Quantification of the accuracy beyond the manufacturer’s accuracy is difficult. 10.2.3 Measurement Error for Parameters See Section 4.2.1. 10.2.4 Additional Quality Assessments Visual review of plots and comparisons of instantaneous data with expected values while in the field were made. 10.2.5 Data Verification by Data Center Data that was loaded into the data tables were spot checked against the original ASCII data that was submitted to check for data loading errors. 11. Notes 11.1 Limitations of the data All data were collected during periods of essentially clear skies. The magnitude of solar radiation cannot be compared between the SSA-OJP and SSA-OBS or SSA-OA because SSA-OJP data were collected during early February when the solar altitude is lower than in early March when OBS and OA data were collected. 11.2 Known Problems with the Data None. 11.3 Usage Guidance A single measurement from one pyranometer alone cannot represent the receipt of radiation on the forest floor. The data set is intended for validation of a radiative transfer model. 11.4 Other Relevant Information None given. 12. Application of the Data Set This data set can be used to understand the variability of solar radiation receipt in both coniferous and deciduous forests and could be used in validating models that predict radiation in forests. 13. Future Modifications and Plans None. 14. Software Any spreadsheet or graphics software can be used to process this data. 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) beth@ltpmail.gsfc.nasa.gov 15.2 Data Center Identification See Section 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-03 subcanopy radiation 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 Contact BORIS staff. 16.2 Film Products Contact BORIS staff. 16.3 Other Products Contact BORIS staff. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Manual available from manufacturer: Eppley Laboratory, Inc. 12 Sheffield Ave. Newport, RI 02840 (401) 847-1020 Datalogger manuals available from: Campbell Scientific Incorporation P.O. Box 551 Logan, UT 84321 (801) 753-2342 (801) 752-3268 (fax) 17.2 Journal Articles and Study Reports Davis, R.E., C. Woodcock, and J.P. Hardy. 1996. Toward spatially distributed modeling of snow in the boreal forest. Eos Transactions, AGU 1995 Fall Meeting, Abstract, p. 218. Davis, R.E., J.P. Hardy, W. Ni, C. Woodcock, C.J. McKenzie, R. Jordan, and X. Li. 1997. Variation of snow ablation in the boreal forest: A sensitivity study on the effects of conifer canopy. Journal of Geophysical Research. 102(D24):29389-29396. Hardy, J.P., R.E. Davis, and J.C. McKenzie. 1995. Snow Distribution Around Trees: Incorporation of snow interception patterns into spatially distributed snow models. Eos Transactions, AGU 1995 Fall Meeting, Abstract, p. 202. Hardy, J.P., R.E. Davis, and R. Jordan. 1996. Snow melt modeling in the Boreal forest. Eos Transactions, AGU 1996 Fall Meeting, Abstract, p. 196. Hardy, J.P., R.E. Davis, R. Jordan, X. Li, C. Woodcock, W. Ni, and J.C. McKenzie. 1997. Snow ablation modeling at the stand scale in a boreal jack pine forest. Journal of Geophysical Research. 102(D24): 29397-29406. Ni, W., X. Li, C.E. Woodstock, J.L. Roujean, and R.E. Davis. 1997. Transmission of solar radiation in boreal conifer forests: Measurements and models. Journal of Geophysical Research. 102(D24):29555-29566. 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.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, F.E. Guertin. 1997. BOREAS in 1997: Experiment overview, scientific results, and future directions. Journal of Geophysical Research. 102(D24):28731-28770. 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. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System CGR - Checked by Group CPI - Checked by Principal Investigator CPI-??? - CPI but questionable CRREL - Cold Regions Research and Engineering Laboratory DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FFC-W - Focused Field Campaign - Winter GSFC - Goddard Space Flight Center GMT - Greenwich Mean Time HYD - Hydrology 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 URL - Uniform Resource Locator 20. Document Information 20.1 Document Revision Dates Written: 23-Apr-1997 Revised: 19-Mar-1998 20.2 Document Review Dates BORIS Review: 12-Jan-1998 Science Review: 15-Jul-1997 20.3 Document ID 20.4 Citation 20.5 Document Curator 20.6 Document URL SOLAR RADIATION HYD03_Subcan_Rad.doc Page 12 of 16 04/17/98