BOREAS RSS-17 Dielectric Constant Profile Measurements Summary The BOREAS RSS-17 team acquired and analyzed imaging radar data from the ESA's ERS-1 over a complete annual cycle at the BOREAS sites in Canada in 1994 to detect shifts in radar backscatter related to varying environmental conditions. This data set consists of dielectric constant profile measurements from selected trees at various BOREAS flux tower sites. The relative dielectric constant was measured at C-band (frequency = 5 GHz) as a function of depth into the trunk of three trees at each site. Measurements were made during April 1994 with an Applied Microwave Corporation field PDP fitted with a 0.358-cm (0.141-inch) diameter coaxial probe tip. 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 RSS-17 Dielectric Constant Profile Measurements 1.2 Data Set Introduction The dielectric constant provides an indication of how a material responds in an electric field. Thus, it is useful to quantify this property in order to interpret radar remote sensing signatures. When considering the microwave frequency spectrum, the dielectric constant of liquid water is much higher than that of other components of a natural landscape. Thus, variations in the amount (moisture content) and state (frozen vs. thawed) of water in a vegetation canopy can significantly affect radar backscatter. The relative dielectric constant was measured as a function of depth into the trunks of three trees at each of seven treed BOReal Ecosystem-Atmosphere Study (BOREAS) tower sites. An Applied Microwave Corporation C-band field portable dielectric probe (PDP) was used to measure these data. Profiles were obtained during April 1994, shortly after the trees thawed. 1.3 Objective/Purpose These measurements were taken to assist with interpretation of radar backscatter measurements obtained with the Earth Resource Satellite-1 (ERS-1) Synthetic Aperture Radar (SAR). The dielectric constant of woody vegetation varies dramatically as the vegetation transitions from a frozen to a thawed state. Because radar backscatter responds to changes in the dielectric constant, these measurements were obtained to verify that the trees had undergone the spring thaw transition. These data may also be used as parameter inputs to radar backscatter models to assist in interpretation of radar remote sensing measurements obtained at the BOREAS sites. 1.4 Summary of Parameters and Variables Each line provides the real and imaginary parts of the relative dielectric constant at a single depth in the trunk of a selected tree of the indicated BOREAS stand. Each of these measurements represents the arithmetic mean of three samples taken at the same location in that tree. For a given tree, a measurement series represents the relative dielectric constant as a function of depth into the tree trunk. 1.5 Discussion The dielectric constant of woody vegetation varies dramatically as the vegetation transitions from a frozen to a thawed state. Because of the fact that radar backscatter responds to changes in dielectric constant, these measurements were obtained to verify that the trees had undergone the spring thaw transition. The relative dielectric constant was measured as a function of depth into the trunks of three trees in each of seven BOREAS tower sites. An Applied Microwave Corporation C-band field PDP was used to measure these data. Profiles were obtained during April 1994, shortly after the trees thawed. 1.6 Related Data Sets BOREAS RSS-15 SIR-C and Landsat TM Biomass and Landcover Maps BOREAS RSS-16 Level-3b DC-8 AirSAR CM Images BOREAS RSS-16 Level-3b DC-8 AirSAR SY Images BOREAS RSS-17 Stem and Air Temperature Measurements BOREAS RSS-17 1994 ERS-1 Level-1 Backscatter Change Images BOREAS RSS-17 Xylem Flux Density Measurements at the SSA-OBS Site 2. Investigators 2.1 Investigator(s) Name and Title Principal Investigator Dr. JoBea Way Jet Propulsion Laboratory Co-Investigator Dr. Kyle McDonald Jet Propulsion Laboratory Co-Investigator Dr. Reiner Zimmermann Bayreuth Institute for Terrestrial Ecosystem Research (BITOEK) 2.2 Title of Investigation Monitoring Environmental and Phenologic State and Duration of State with SAR as Input to Improved CO2 Flux Models 2.3 Contact Information Contact 1 --------- Dr. JoBea Way Jet Propulsion Laboratory California Institute of Technology Pasadena, CA (818) 354-8225 (818) 354-9476 (fax) way@lor.jpl.nasa Contact 2 --------- Dr. Kyle McDonald Jet Propulsion Laboratory California Institute of Technology Pasadena, CA (818) 354-3263 (818) 354-9476 (fax) kyle.mcdonald@jpl.nasa.gov Contact 3 --------- Dr. Reiner Zimmermann Bayreuth Institute for Terrestrial Ecosystem Research (BITOEK) Plant Ecology II University of Bayreuth Germany reiner.zimmermann@bitoek.uni-bayreuth.de 3. Theory of Measurements The relative dielectric constant is monitored with an Applied Microwave Corporation field PDP. The PDP used here measures the complex reflection coefficient (magnitude and phase) at the point of contact between a material of unknown dielectric constant and a semi-rigid coaxial probe tip. The reflection coefficient was measured at a frequency of 5 GHz, corresponding to the C-band portion of the electromagnetic spectrum. The real and imaginary parts of the relative dielectric constant are determined from the complex reflection coefficient through application of a calibration equation determined from measurements of reflection coefficient made on a series of reference dielectric liquids. 4. Equipment 4.1 Sensor/Instrument Description The dielectric constant was measured with a field PDP manufactured by Applied Microwave Corporation, Lawrence, KS. These instruments are no longer in production. 4.1.1 Collection Environment Data were collected in April 1994. Air temperature was above 0 °C. Weather conditions varied from cool and clear to rainy. 4.1.2 Source/Platform The PDP is a hand-held, field portable device. 4.1.3 Source/Platform Mission Objectives This study was undertaken to combine ERS-1 SAR with ecosystem CO2 flux models. The objective is to use SAR observations as direct inputs to these models to improve their estimates of seasonal CO2 flux. 4.1.4 Key Variables Relative dielectric constant (C-band). 4.1.5 Principles of Operation The PDP provides a direct measurement of the complex reflection coefficient. The relative dielectric constant is inferred through application of a calibration transformation equation determined from an equivalent circuit model applied to the coaxial probe tip. The parameters of the calibration transformation equation are determined from measurements taken on a series of liquids of known dielectric constant. 4.1.6 Sensor/Instrument Measurement Geometry The dielectric constant was inferred from measurements of the complex reflection coefficient measured at the interface of a 0.358 cm (0.141 inch) diameter semi- rigid coaxial probe tip and with an unknown dielectric constant, the tree trunk. 4.1.7 Manufacturer of Sensor/Instrument Applied Microwave Corporation, Lawrence, KS The PDP is no longer in production. 4.2 Calibration Calibration and processing of the dielectric data was performed with Mathematica 2.0 for the Macintosh (Wolfram Research, Inc.). The calibration technique is described in the PDP manual (1989) and by Dobson (1990). 4.2.1 Specifications None given. 4.2.1.1 Tolerance None given. 4.2.2 Frequency of Calibration Calibration against a series of dielectric liquids was performed in the laboratory at JPL shortly before going to the BOREAS sites in April. In-field calibration checks are performed against an air standard immediately before each dielectric measurement. 4.2.3 Other Calibration Information Not available. 5 Data Acquisition Methods Profiles of the relative dielectric constant were obtained for each tree by drilling a small hole in the tree trunk to the desired depth, measuring the depth of the hole with a caliper, inserting the coaxial probe tip, and measuring the complex reflection coefficient. The process is repeated in the same hole, drilled successively deeper, until a point near the center of the tree trunk is reached, or until the probe tip cannot be inserted any further. Data are stored in a hand-held computer and loaded onto a PC for post-processing. A series of three measurements was obtained at each depth. The values for the relative dielectric constant provided in the data file were computed by averaging the three values of dielectric constant obtained from these measurements. 6. Observations 6.1 Data Notes The time values for the SSA-OA site on April 20 do not change except for the last few record on that day. The clock on the calculator was not set properly. The measurements acquired at time = 14.00 (20:00 GMT) were collected at approximately 14:00 +/- 15 minutes according to field notes. The calculator's internal clock was re-set to correct the time problem at 14.24 (16:24 GMT). As this data set is not time-critical over the acquisition period of each profile, this will have no effect on the data quality. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage Each measurement is taken from one tree within a stand. Groups of three individual trees were measured at the BOREAS tower sites. The following North American Datum of 1983 (NAD83) site locations were sampled in the NSA and SSA: Site UTM Zone UTM Northing UTM Easting ------- -------- ------------ ----------- NSA-OBS 14 6192853.4 532444.5 NSA-YJP 14 6194706.9 544583.9 NSA-OJP 14 6198176.3 523496.2 SSA-YJP 13 5969762.5 523320.2 SSA-OJP 13 5974257.5 520227.7 SSA-OBS 13 5982100.5 492276.5 SSA-OA 13 5942899.9 420790.5 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The spatial resolution of a given measurement is one tree. A series of records corresponding to a single tree and tower site corresponds to one dielectric profile. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Data collection took place from 19 - 28 April 1994. 7.2.2 Temporal Coverage Map The dates when the various sites were measured are: SSA-OA 19-April-1994 SSA-OBS 20-April-1994 SSA-YJP 21-April-1994 SSA-OJP 25-April-1994 NSA-YJP 27-April-1994 NSA-OBS 28-April-1994 NSA-OJP 28-April-1994 7.2.3 Temporal Resolution One measurement of dielectric constant takes less than 1 minute. Measurements at each tree were taken at 2- to 4- minute intervals. A complete profile series can be completed within 1 hour. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (rs17diel.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (rs17diel.def). 8. Data Organization 8.1 Data Granularity All of the Dielectric Constant Profile Measurements 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. Each record corresponds to a single measurement of dielectric constant. A series of records corresponding to a single tree and tower site corresponds to one dielectric profile. Sample data records are shown in the companion data definition file (rs17diel.def). 9 Data Manipulations 9.1 Formulae None given. 9.1.1 Derivation Techniques and Algorithms The data files on CD-ROM contain a series of numerical and character fields of varying length separated by commas. The character fields are enclosed within single apostrophe marks. There are no spaces between the fields. 9.2 Data Processing Sequence 9.2.1 Processing Steps None given. 9.2.2 Processing Changes Not applicable. 9.3 Calculations 9.3.1 Special Corrections/Adjustments Not applicable. 9.3.2 Calculated Variables None given. 9.4 Graphs and Plots Not available. 10. Errors 10.1 Sources of Error Instabilities in the electronics of the PDP are taken into account by repeated calibration of the PDP with free space as the calibration standard. Accuracy of the dielectric constant measurement is limited by the range of the dielectric constant of the liquid standards used in laboratory calibration of the PDP. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgment Accuracy of the dielectric constant is estimated to be +/- 10% when the real portion, Re(eps), is less than 15 and when the imaginary portion, Im(eps), is less than 4. The accuracy of the dielectric constant decreases to +/- 30% when Re(eps) is greater than 15 and Im(eps) is greater than 4, where eps is the complex relative dielectric constant. 10.2.3 Measurement Error for Parameters Not available. 10.2.4 Additional Quality Assessments Not applicable. 10.2.5 Data Verification by Data Center Data have been checked for content as described and for format. 11 Notes 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data None given. 11.3 Usage Guidance These data are typically used to estimate the gross vegetation dielectric constant for application to radar remote sensing studies (e.g., Way, et al., in press). 11.4 Other Relevant Information Not available. 12 Application of the Data Set Site-level observations related to the state of the stand or the forest, either frozen or thawed. 13 Future modifications and plans. None. 14. Software 14.1 Software Description Data collection and preprocessing of the PDP data files were performed with custom software written for the HP hand-held computer at the University of Michigan radiation laboratory. Calibration and processing of the dielectric data were performed with Mathematica 2.0 for the Macintosh (Wolfram Research, Inc.) 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 Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or . 15.4 Data Center Status/Plans The RSS-17 dielectric constant data 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 data are available as tabular ASCII files. 17 References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Applied Microwave Corporation. 1989. Manual for Portable Dielectric Probe. Applied Microwave Corporation. Lawrence, KS. 17.2 Journal Articles and Study Reports Brunfeldt, D.R.. 1997. Theory and Design of a Field-Portable Dielectric Measurement System. Proc. of the 1987 International Geoscience and Remote Sensing Symposium. Ann Arbor, Michigan, May 18-21, pp. 559-563. Dobson, M.C., "Calibration of field portable dielectric probes for use in radar experiments." May 1990. Radiation Laboratory Technical Report. The University of Michigan, Ann Arbor. Hogg, E. H., T. A. Black, G. den Hartog, H. H. Neumann, R. Zimmerman, P. A. Hurdle, P. D. Blanken, Z. Nesic, P. C. Yang, R. M. Staebler, K. McDonald, and R. Oren. 1997. A Comparison of Sap Flow and Fluxes of Water Vapour from a Boreal deciduous forest. Journal of Geophysical Research (JGR), BOREAS Special Issue, 102(D24), Dec. 1997, pp. 28929-28937. 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): 28,731-28,770. Way, J.B., R. Zimmermann, E. Rignot, K. McDonald, and R. Oren. Winter and spring thaw as observed with imaging radar at BOREAS. Journal of Geophysical Research (JGR), BOREAS Special Issue, 102(D24), Dec. 1997, pp. 29673-29684. 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 DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System ERS-1 - Earth Resources Satellite -1 GSFC - Goddard Space Flight Center 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 PDP - Portable Dielectric Probe RSS - Remote Sensing Science SAR - Synthetic Aperature Radar SSA - Southern Study Area URL - Uniform Resource Locator (a World Wide Web address) UTM - Universal Transverse Mercator YJP - Young Jack Pine 20. Document Information 20.1 Document Revision Date(s) Written: 10-Jun-1997 Last Updated: 06-Oct-1998 20.2 Document Review Date(s) BORIS Review: 10-Sep-1997 Science Review: 31-Oct-1997 20.3 Document ID 20.4 Citation Please acknowledge K.C. McDonald, J.B. Way, and R. Zimmermann for providing the data. 20.5 Document Curator 20.6 Document URL Keywords Dielectric Boreal Forest Freeze/Thaw C-band RSS17_Dielectric_Prof.doc 10/09/98