BOREAS RSS-01 PARABOLA SSA Surface Reflectance and Transmittance Data Summary The BOREAS RSS-01 team collected surface reflectance and transmittance data from three forested sites in the SSA. This data set contains averaged reflectance factors and transmitted radiances measured by the PARABOLA instrument at selected sites in the BOREAS SSA at different view angles and at three wavelength bands throughout the day. PARABOLA measurements were made during each of the three BOREAS IFCs during the growing season of 1994 at three SSA tower flux sites as well as during the FFC-T. Additional measurements were made in early and mid-1996 during the FFC-W and during IFC-2. 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-01 PARABOLA SSA Surface Reflectance and Transmittance Data 1.2 Data Set Introduction The Portable Apparatus for Rapid Acquisitions of Bidirectional Observations of Land and Atmosphere (PARABOLA) is an instrument specifically designed to measure variations in reflectance of forest canopies as a function of solar and sensor viewing geometry, wavelength, and canopy biophysical characteristics. These data are averaged reflectance factors and transmitted radiance values of selected sites in the BOReal Ecosystem-Atmosphere Study (BOREAS) Southern Study Area (SSA) at different view angles within three wavelength regions throughout the day. The raw data for each channel during each aquisition were binned by creating 144 conical bins within the spherical space that surrounds the instrument; the data points that fell within each bin were then averaged. 1.3 Objective/Purpose This study had the following objectives: 1) Characterize the multidirectional interactions of solar energy in various types of boreal forest canopies through intensive measurements and modeling 2) Relate these characteristics to ecologically important biophysical parameters 3) Provide bidirectional reflectance measurements of the various boreal forest canopies 4) Determine the variability of reflected and emitted radiation in selected spectral wavebands as a function of canopy type, phenological growth stage, and solar zenith angle (SZA) 5) Estimate surface albedo and Photosynthetically Active Radiation (PAR) albedo from bidirectional reflectance and irradiance data. The PARABOLA allowed for rapid acquisition of bidirectional observations of the land and atmosphere, by measurement of the angular distributions of reflected and transmitted radiation of natural earth surface targets. Its specific purpose was to provide bidirectional reflectance measurements of the various boreal forest canopy types. 1.4 Summary of Parameters Radiance, reflectance, and illumination and viewing angles. 1.5 Discussion PARABOLA is an instrument specifically designed to measure variations in vegetation reflectance as a function of solar and sensor viewing geometry, wavelength, and plant canopy biophysical characteristics. The data are averaged reflectance factors and transmitted radiances of selected sites in the BOREAS SSA at different view angles and in three wavelength regions throughout the day. The raw data for each channel and time period were binned by creating 144 conical bins within the spherical space that surrounds the instrument. The measured data points that fell within each bin were then averaged. PARABOLA measurements were made during the Focused Field Campaign-Thaw (FFC-T) as well as during each of the three BOREAS Intensive Field Campaigns (IFCs) in 1994 at three tower sites within the BOREAS SSA. Measurements also were made during the Focused Field Campaign-Winter (FFC-W) and during IFC-2 in 1996. 1.6 Related Data Sets BOREAS RSS-02 Level-1b ASAS Imagery: At-sensor Radiance in BSQ Format BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted Barnes MMR BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted SE-590 BOREAS RSS-11 Ground Network of Sunphotometer Measurements BOREAS RSS-12 Automated Ground Sunphotometer Measurements in the SSA BOREAS RSS-18 Level-1B AVIRIS Imagery: At-sensor Radiance in BIL Format BOREAS RSS-19 Level-1B CASI Imagery: At-sensor Radiance in BIL Format BOREAS RSS-20 POLDER Measurements of Surface BRDF 2. Investigator 2.1 Investigator(s) Name and Title Dr. Donald W. Deering, Principal Investigator Dr. Elizabeth M. Middleton, Co-Investigator Dr. Suraiya P. Ahmad, Co-Investigator Mr. Thomas F. Eck, Co-Investigator 2.2 Title of Investigation Radiative Transfer Characteristics of Boreal Forest Canopies and Algorithms for Energy Balance and PAR Absorption 2.3 Contact Information Contact 1 ---------- Dr. Donald W. Deering NASA GSFC Greenbelt, MD (301) 286-9186 (301) 286-0239 (fax) Donald.Deering@gsfc.nasa.gov Contact 2 ---------- Thomas F. Eck Raytheon ITSS NASA GSFC Greenbelt, MD (301) 286-6559 (301) 286-0239 Thomas.Eck@gsfc.nasa.gov Contact 3 ------------- Jaime Nickeson Raytheon ITSS NASA GSFC Greenbelt, MD (301) 286-3373 (301) 286-0239 (fax) Jaime.Nickeson@gsfc.nasa.gov 3. Theory of Measurements The focus of this research was to characterize the variation in vegetation reflectance as a function of solar and sensor viewing geometry, wavelength, and plant canopy biophysical characteristics. An understanding of these relationships is necessary for meaningful biophysical and ecological interpretations of measurements acquired from airborne and satellite sensors. PARABOLA can measure these variations in reflectance because it measures at different viewing angles and at three spectral bands. Light radiation striking a vegetative canopy interacts with individual phytoelements (leaves, stems, branches) and the underlying substrate. The interaction depends on light quality, radiative form (direct or diffuse), illumination incidence angle, vegetative component optical properties, and canopy architecture. Radiation is reflected, transmitted, or absorbed. Researchers have shown that phytoelements and substrates are not perfect Lambertian reflectors; i.e., they do not reflect equally in all directions (Walter-Shea, et al., 1989; Irons et al., 1989). The amount of leaf area and the leaf angle distribution will determine the amount of vegetation and substrate that is sunlit and shaded. The amount of vegetation and substrate and respective amounts of sunlit and shaded components in a scene will vary depending on the angle at which it is viewed; i.e., the canopy is itself a non-Lambertian surface. Thus, canopy illumination and viewing geometry are critical in determining the amount of reflected radiation received at the sensor. Reflected radiation measurements were converted to radiance and reflectance factors (the ratio of reflected radiance to incident radiance). The reflectance factor is the ratio of the target reflected radiant flux to an ideal radiant flux reflected by an ideal Lambertian standard surface irradiated in exactly the same way as the target. Reflected radiation from a field reference panel corrected for non-perfect reflectance and Sun angle was used as an estimate of the ideal Lambertian standard surface (Walter-Shea and Biehl, 1990). 4. Equipment 4.1 Sensor/Instrument Description The basic PARABOLA instrument is a three-channel, rotating-head radiometer consisting of three primary units: the sensor head, the data recording unit, and the internal power pack. The sensor head is composed of a motor-driven tow-axis gimbal on which three detector units are jointly mounted. The three detectors include two silicon and one germanium solid-state detectors, with filters configured to correspond to Thematic Mapper (TM) spectral bands 3, 4, and 5 (630-690, 760-900, and 1550-1750 nm), respectively. They are temperature- regulated (by cooling or heating) through thermoelectric proportional control circuits. Also, because of the tremendous range in target brightness that can be expected in scanning a two-hemisphere field of view (FOV), an auto-ranging amplifier is used to switch the gain levels back and forth by factors of 1, 10, and 100 to maintain maximum radiometric sensitivity. The detector cones confine the FOV to 15-degrees. The two-axis, two-motor rotation of the head enables a near-complete sampling of the entire sky/ground sphere. There is a 15 degree exclusion area toward the mounting device because of mechanical limitations. 4.1.1 Collection Environment The PARABOLA instrument was mounted on a tram which traversed a fixed set of tram cables at each of the 3 BOREAS Tower/Tram sites in the Southern Study Area (SSA) (Old Aspen, Old Jack Pine, and Old Black Spruce). The tram cabling height was approximately 13-14 meters above the height of the forest canopy at each site. PARABOLA measurements were made on days of 0 to 30% cloud cover, beginning at about 75 degrees solar zenith angle to solar noon. 4.1.2 Source/Platform PARABOLA's two-axis motorized radiometer and leveling head, with a camera- mounting attachment, were mounted on a tram that traversed a fixed set of tram cables at each of the three BOREAS Tower/Tram sites in the SSA Old Aspen (OA), Old Jack Pine (OJP), and Old Black Spruce (OBS). The tram cabling height was approximately 13-14 meters above the height of the forest canopy at each site. PARABOLA data measurement scans were made at distances from the principal scaffold flux tower ranging from 25 meters to 5 meters at 2-meter increments. This resulted in PARABOLA scans being taken at 11 subsites along the tram transect for each SZA set. All operations of PARABOLA and the adjacent canopy wide angle camera were controlled from PARABOLA's data system control panel on the flux tower. PARABOLA measurements were also taken on under-canopy trams at 4 meters above ground level with the same sampling interval as the above-canopy measurements for both the OA and the OJP data sets. For the OBS site, under- canopy measurements were taken with the instrument mounted on a large tripod that was lifted and moved manually for spatial sampling. 4.1.3 Source/Platform Mission Objectives The purpose of the installed towers and tram wires were to provide a place on which the PARABOLA could rest and obtain measurements. 4.1.4 Key Variables Radiances, reflectance, and viewing angle. 4.1.5 Principles of Operation The scan system is designed such that sampling is done in a continuous helical pattern. The data are recorded serially in digital form. There is also a "calibrate"/hold position (mode) that allows manual pointing of the detector head for individual measurements of calibration sources in any direction. In the helical sampling mode, a complete data set can be taken in 11 seconds followed by a data dump to a portable PC from the buffer. 4.1.6 Sensor/Instrument Measurement Geometry PARABOLA's design provides multidirectional viewing, but the system's geometry does not allow the same "spot" on the ground to be measured at each view direction. Thus, target surfaces that are homogeneous over relatively large areas are sampled with replication. Routinely, 11 subsites were sampled along each BOREAS tram transect to minimize any within-field heterogeneity effects and to improve the sensitivity to angular reflectance features of the surfaces. The 15-degree internal field of view (FOV) of the sensor provides "viewing areas" that are similar in scale relative to the spatial structure of the surfaces measured. The various pixels range from approximately 5.4 square meters at nadir to approximately 46.6 square meters at an off nadir angle of 60 degrees. 4.1.7 Manufacturer of Instrument National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) Biospheric Sciences Branch Greenbelt, MD 20771 4.2 Calibration Radiometric laboratory calibration of PARABOLA was performed at NASA GSFC on a 1.8-m spherical integrator using 12 200-W quartz halogen lamps (2950 K at 6.5 A). The number of lamps illuminating the sphere is varied to produce 12 radiance levels for calibration. No field calibration was performed. 4.2.1 Specifications Laboratory Calibration: Three separate calibration runs are made to fully calibrate PARABOLA at a wide range of radiance levels. Neutral density filters (0.1 density level) are used for the lowest gain setting. The voltage response to radiance level relationship is linear in all three spectral channels for each gain setting with correlation coefficients of 0.999. 4.2.1.1 Tolerance None given. 4.2.2 Frequency of Calibration Laboratory Calibration: The last PARABOLA calibration was done on 02-Oct-1996. The PARABOLA instrument is calibrated using the GSFC 1.8 m integrating sphere (located in Bldg. 22) as the standard radiance source. The PARABOLA instrument was calibrated against the 1.8 m sphere before the FFC-T on 28-Mar-1994, between IFC-1 and -2 on 24-Jun-1994, and after IFC-3 on 04-Oct-1994. Measurements are made with and without a nominal 10% neutral density filter for the 12 lamp levels of the 1.8 m sphere. 4.2.3 Other Calibration Information None. 5. Data Acquisition Methods Data were acquired from the PARABOLA instrument mounted on a tram system that traversed a fixed set of cables at each of the three BOREAS Tower/Tram sites in the SSA OA, OJP, and OBS). The tram cabling height was approximately 13-14 meters above the height of the forest canopy at each site. PARABOLA data measurement scans were made at distances from the principal scaffold flux tower ranging from 5 meters to 25 meters at 2-meter increments. This resulted in PARABOLA scans being taken at 11 subsites along the tram transect for each SZA set. All operations of PARABOLA and the adjacent canopy wide angle camera were controlled from the PARABOLA data system control panel on the flux tower. PARABOLA measurements were also taken on under-canopy trams at 4 meters above ground level with the same sampling interval as the above-canopy measurements for both the OA and the OJP data sets. For the OBS site, under-canopy measurements were taken with the instrument mounted on a large tripod that was lifted and moved manually for spatial sampling (see Section 9.2 for details). 6. Observations 6.1 Data Notes The solar zenith angle views that were provided with the data represented a solar angle at the end time of the data acquisition period. Solar aziumth angles were not provided in the original data files. BORIS calculated both the solar azimuth and zenith angles from location, date, and GMT, and loaded these values with the PARABOLA data. In general, it took about 20 minutes for a PARABOLA data acquisition at one site and solar zenith angle. The solar zenith would range at most 1.5 degrees during this time. The accquisition time increased during the summer IFC in 1996, with solar zenith angle ranging as much as 3.7 degrees. This was due to the fact that during this IFC, the RSS-01 team was also testing the new PARABOLA III instrument, which increased the overall data collection time. The column PARABOLA_MEAN_VIEW_AZ_ANG is reported as an angle relative to the solar principle plane. To caculate this angle relative to North, add the SOLAR_AZ_ANG column to the PARABOLA_MEAN_VIEW_AZ_ANG. If the result is greater than 360 degrees, subtract 360 to get the correct value relative to North. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage The PARABOLA data were collected at the following three SSA locations along the tram cable systems erected between the principal scaffold flux tower and a Rohn tower located approximately 70 m from the flux tower. 1. Old Aspen (SSA-9OA) 2. Old Jack Pine (SSA-OJP) 3. Old Black Spruce (SSA-OBS) The NAD83 site coordinates: ----------------------------------------------------------------------------- UTM UTM UTM Site Id Longitude Latitude Easting Northing Zone ----------------------------------------------------------------------------- SSA-9OA-PRB01 106.19779° W 53.62889° N 420790.5 5942899.9 13 SSA-OJP-PRB01 104.69203° W 53.91634° N 520227.7 5974257.5 13 SSA-OBS-PRB01 105.11779° W 53.98717° N 492276.5 5982100.5 13 ----------------------------------------------------------------------------- 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The spatial resolution of the data ranges from 5.4 square meters at nadir to 15.6 square meters at an angle of 45 degrees off-nadir and 46.6 square meters at 60 degrees off-nadir. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics. 7.2.1 Temporal Coverage The overall period of PARABOLA data acquisition was from 16-Apr-1994 through 30- Jul-1996. 7.2.2 Temporal Coverage Map The following table lists the data that were integrated into BORIS and are being provided on the BOREAS CD-ROM series. For information about additional data that were collected, see Sections 15 and 16. NUMBER OF SOLAR ZENITH PARABOLA DATE IFC# SITE ANGLE VIEWS POSITION ---------------------------------------------------------- 16-Apr-94 FFC-T SSA-OBS 4 Above Canopy 17-Apr-94 FFC-T SSA-OBS 1 Above Canopy 19-Apr-94 FFC-T SSA-OBS 6 Above Canopy 24-Apr-94 FFC-T SSA-OA 4 Above Canopy 25-Apr-94 FFC-T SSA-OA 1 Above Canopy 25-May-94 1 SSA-OA 3 Above Canopy 26-May-94 1 SSA-OA 3 Above Canopy 31-May-94 1 SSA-OJP 8 Above Canopy 7-Jun-94 1 SSA-OBS 8 Above Canopy 11-Jun-94 1 SSA-OA 5 Above Canopy 21-Jul-94 2 SSA-OA 6 Above Canopy 25-Jul-94 2 SSA-OJP 9 Above Canopy 4-Aug-94 2 SSA-OBS 6 Above Canopy 31-Aug-94 3 SSA-OA 6 Above Canopy 6-Sep-94 3 SSA-OJP 6 Above Canopy 13-Sep-94 3 SSA-OBS 6 Above Canopy 17-Sep-94 3 SSA-OA 7 Above Canopy 5-Mar-96 FFC-W SSA-OBS 3 Above Canopy 8-Mar-96 FFC-W SSA-OA 2 Above Canopy 12-Mar-96 FFC-W SSA-OJP 2 Above Canopy 20-Jul-96 IFC-2-96 SSA-OJP 1 Above Canopy 29-Jul-96 IFC-2-96 SSA-OBS 1 Above Canopy 30-Jul-96 IFC-2-96 SSA-OBS 1 Above Canopy 7.2.3 Temporal Resolution PARABOLA data were collected at 5-degree SZA intervals, clouds permitting, from approximately 75 degrees SZA to solar noon. The PARABOLA measures a four- hemisphere area with 15-degree IFOV sectors in 11 seconds. Measurements of the reflected radiance from a characterized barium sulfate (BaSO4) reference panel were taken concurrently with PARABOLA measurements during the BOREAS experiment in order to characterize spectral solar irradiance. These BaSO4 measurements were made with a Barnes Modular Multiband Radiometer (MMR) mounted approximately 0.4 meters above a horizontally leveled BaSO4 panel so that the MMR viewed the panel with a nadir view angle. The MMR scanned the panel continuously throughout the day, and a Polycorder data logger was set to record the measurements at a 1- minute time step interval. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (rss1para.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (rss1para.def). 8. Data Organization 8.1 Data Granularity All reflectance and transmittance data are in one file. 8.2 Data Format(s) The data files contain American Standard Code for Information Interchange (ASCII) 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 (rss1para.def). 9. Data Manipulations 9.1 Formulae None given. 9.1.1 Derivation Techniques and Algorithms Characterization of spectral solar irradiance was carried out using two separate techniques. First, a Barnes MMR was mounted above a BaSO4 reference panel, both clamped to the tower above the canopy top in order to sample the spectral downwelling irradiance. The MMR and PARABOLA were intercalibrated at the GSFC 1.8-m integrating sphere radiance source. The MMR measurements of the BaSO4 panel were corrected for reflectance anisotropy, which had been previously characterized using the procedure of Jackson et al. (1987). However, because of different band passes of the PARABOLA and MMR instruments (e.g. PARABOLA 810-840 nm versus MMR 750-880 nm), the MMR response to different total columnar atmospheric water vapor amount differed from PARABOLA's response due to different water vapor transmittances. Therefore, the cloudless sky spectral irradiance model was used (an integral part of the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) model (Vermote et al., 1997)). The model was used with measured aerosol optical depths, total water vapor, and aerosol volume size distributions from Cimel automatic spectral solar radiometers located in the BOREAS SSA (Markham et al. (1997)). The total ozone amount used in the 6S model calculations was climatological means from London et al. (1976). For PARABOLA channel 1 (650-670 nm; with no water vapor absorption), the irradiances computed from 6S agreed very well with MMR measured irradiances, typically within 2-3%. However, for PARABOLA channel 2 (810-840 nm), the differences between the two techniques varied from approximately 1% to 15% depending on water vapor amount and SZA. Differences between the two techniques for PARABOLA channel 3 (1620-1690 nm) were intermediate to those found for the other channels, since the water vapor transmittance differences for the two instrument band passes were less in channel 3 than for channel 2. Therefore, because of the differing effects of the water vapor transmittances for the differing band passes of the two instruments, the spectral irradiance computed from 6S was used in the calculations of reflectance factors. 9.2 Data Processing Sequence 9.2.1 Processing Steps Directional reflectances are normally computed as hemispherical-directional reflectance factors using the PARABOLA directional radiance measurements from the ground-looking hemisphere. The ground-looking hemisphere values are divided by the PARABOLA-derived incident irradiance as computed from the PARABOLA sky irradiance data or from a calibrated BaSO4 painted reference standard panel. The PARABOLA data scans taken from the 11 subsites at each SZA measurement sequence are combined in software written to analyze the bidirectional reflectance distribution characteristics of the site. This procedure also enables more accurate sampling of the "hot spot" effects and the aureole surrounding the Sun. Because the PARABOLA observations are not acquired at equal angles of azimuth and zenith, and because most users prefer the data at equal intervals, these data have been averaged into standard bins. A data aggregation scheme was established that defines bins of 30 degrees of azimuth and 15 degrees of zenith for each of the sky and ground hemispheres, resulting in (360/30) * (90/15) bins (i.e., 12 * 6 = 76 bins) per hemisphere. The observed pixels falling in a given bin were averaged to derive the supplied radiance value. The number of pixels used in computing the bin average is contained in the column NUM_OBS. Data gaps resulting from the scanning pattern, shadowing, or contamination of the pixel by instrument support equipment or operators and/or other anomalies are handled as follows: ? If data are available from the opposite side of the hemisphere, the data gap is filled by placing the information from the opposite side into the empty area. Note that this assumes symmetry in the azimuth plane with respect to the solar principal plane. These instances are identified with a negative number of observations. ? If no data are available from the opposite side of the hemisphere, an interpolated value is used. These instances are identified with a zero in the number of observations column. BOREAS Information System (BORIS) Processing Steps for PARABOLA data: 1) Reformatted the PARABOLA .AFF files to add date, time, hemisphere, solar azimuth, and reflectance columns. 2) Computed the SZA and solar azimuth angles based on site location, observation date, and observation time. Replaced the SZA given with that which was computed because the angles in the original files were computed from an end time rather than the mid-point of the data collection time. Entered the solar azimuth. 3) Calculated reflectance from radiance using the Barium Sulfate measurements given. The BaSO4 measurement values are contained within the table RSS01_PARABOLA_BASO4_REF. 4) Computed NDVI from the reflectance values. 4) Loaded and inventoried the data in to the BORIS database. 5) Extracted the PARABOLA data to create files for each date and site. 9.2.2 Processing Changes None given. 9.3 Calculations See Section 9.1.1. 9.3.1 Special Corrections/Adjustments Because most users prefer the data at equal intervals of viewing angles, an averaged data set is provided. The pixels falling in a cell or bin of fixed off-nadir and azimuth width are averaged. The centers of these bins are at intervals of 15 degrees in off-nadir and 30 degrees in azimuthal plane. One of the columns gives the number of points used in computing the average values for that bin. If there is a data gap caused by the scanning pattern, shadowing of the target by the instrument, or its support equipment (or "contaminated" by the instrument or operators), or other anomalies (e.g., instrument "noise"), the gap is filled by substituting the data point from the opposite side of the hemisphere (assumes symmetry in azimuth plane with respect to the solar principal plane). To identify such cases, the number of data points averaged is given as negative (mirror image) values. If for some reason there are no data for substitution then an interpolated value is used. Because the interpolated values are not real measured values a zero is placed in the column specifying the number of points averaged in order to caution the user about this potential reliability factor. 9.3.2 Calculated Variables See Section 9.1.1. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error None given. 10.2 Quality Assessment The PARABOLA instrument data quality and accuracy are discussed in detail in the the following references: Deering, D.W., and P. Leone. 1986. A sphere-scanning radiometer for rapid directional measurements of sky and ground radiance. Remote Sens. Environ. 19:1- 24. Deering, D.W., Middleton, E.M., Irons, J.R., Blad, B.L., Walter-Shea, E.A., Hays, C.J., Walthall, C., Eck, T.F., Ahmad, S.P., and Banerjee, B.P. (1992), Prairie grassland bidirectional reflectances measured by different instruments at the FIFE site, J. Geophys. Res., 97(D17), 18887-18903. 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgment None given. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessment 10.2.5 Data Verification by Data Center BORIS staff applied a general Quality Assurance (QA) procedure to the data before the steps described in Section 9 were applied. 11. Notes 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data It is recommended that users read Deering and Leone (1986) before using the PARABOLA data. 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set Data can be used to characterize directional anisotropy of solar radiance reflected from terrestrial surfaces and BRDF modeling and validation. PARABOLA data can also be used to estimate hemispherical reflectance (albedo). 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 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 RSS-01 PARABOLA 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 Note that the other (‘FFL’) data sets (described below) are available but were not loaded into the BOREAS data base and are not contained on the CD-ROM series; however, they are available from Oak Ridge National Laboratory (ORNL) (see Section 15). For PARABOLA-data users there are two output PARABOLA data formats that have been created, which have the filename extensions ‘AFF’ and ‘FFL’. The data loaded into the BOREAS data base and described in section 7 were the ‘AFF’ type. The 'FFL' data type is a complete, but filtered, data set consisting of almost all of the individual pixels from the replicate scans (usually 11 for BOREAS sites) of the same target. Because of the scanning pattern of the PARABOLA, the pixels are not at equidistant angles in the off-nadir or azimuth viewing planes. It is recommended that users familiarize themselves with the instrument by reviewing the article by Deering and Leone (1986) before using the PARABOLA data. OUTPUT FORMAT FOR FILE 'filename.FFL': The first record gives the following HEADER INFORMATION: 1. Filename or dataID, extracted from first input filename 2. Hemisphere-ID, 'GR' for ground, ..'SK' for sky 3. Latitude of the target site (-ve for south) 4. Longitude of the target (-ve for west of Greenwich) 5. Date of the observations (e.g., 06-04-1987) 6. Local time of the measurements, hours:min (e.g., 15:22) 7. Julian day (e.g., 155) 8. Greenwich Mean Time (GMT) time of measurements, hours:min (e.g., 20:22) 9. SZA. 10,11,12. Total hemispheric diffuse flux (upwelling or downwelling (W/m2/µm) for channels 1, 2, and 3 respectively. Please note that for the BOREAS data set, a negative sign is put in front of these flux values to caution the user that these values will be updated in the near future once the algorithm is tested and validated for the extrapolation mechanism used beyond 75-degree off-nadir view angles. DATA RECORDS follow the header record. First, all GROUND pixels are written; then the SKY pixels are written following the ground pixels. However, before starting the first sky pixel, the header record is repeated. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Deering, D.W. and P. Leone. 1986. A sphere-scanning radiometer for rapid directional measurements of sky and ground radiance. Remote Sens. Environ. 19:1- 24. 17.2 Journal Articles and Study Reports Ahmad, S.P., E.M. Middleton, and D.W. Deering. 1987. Computation of Diffuse Sky Irradiance from Multidirectional Radiance Measurements. Remote Sens. Environ. 21:185-200. Deering, D.W. 1989. Field Measurements of Bidirectional Reflectance. In: Theory and Applications of Optical Remote Sensing. John Wiley & Sons, Inc. pp. 14-65. Deering, D.W. and T.F. Eck. 1987. Atmospheric Optical Depth Effects on Angular Anisotropy of Plant Canopy Reflectance. Int. J. Remote Sens. 8:893-916. Deering, D.W., E.M. Middleton, J.R. Irons, B.L. Blad, E.A. Walter- Shea, C.J. Hays, C.W. Walthall, T.F. Eck, S.P. Ahmad, and B.P. Banerjee. 1992. Prairie Grassland Bidirectional Reflectance Measured by Different Instruments at the FIFE Site. J. Geophys. Res., 97(D17), 18887-18903. Deering, D.W., T.F. Eck, and J. Otterman. 1990. Bidirectional Reflectances of Three Desert Surfaces and Their Characterization Through Model Inversion. J. Agric. and Forest Meteorol. 52:71-93. Irons, J.R., F.G. Huegel, and R.R. Irish. 1989. Prairie grass hemispherical reflectances from airborne multi-directional observations. Proc. of 19th Conf. on Agriculture and Forest Meteorology and the Ninth Conf. on Biometeorology and Aerobiology. March 7-10, 1989. Charleston, SC. Published by American Meteorological Society, Boston, MA. Irons, J.R., R.A. Weismiller, and G.W. Peterson. 1989. Soil reflectance. G. Asrar (ed.). In Theory and Applications of Optical Remote Sensing. John Wiley & Sons. New York. pp. 66-106. Jackson, R.D., M.S. Moran, P.N. Slater, and S.F. Bigger. 1987. Field calibration of reference reflectance panels. Remote Sens. Environ., 17:37-53. Leshkevich, G.A., D.W. Deering, T.F. Eck, and S.P. Ahmad. 1990. Diurnal Patterns of the Bidirectional Reflectance of Freshwater Ice. Annals of Glaciol. 14:153- 157. London, J., R.D. Bojkov, S. Oltmans, J.I. Kelley. 1976. Atlas of the Global Distribution of Total Ozone July 1957-June 1967. NCAR Tech. Note 113+STR, Boulder, CO. 276 pp. Markham, B.L., J.S. Schafer, B.N. Holben, and R.N. 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Application of Hapke Photometric Model to Lunar Lake Playa Using PARABOLA Bidirectional Reflectance Data. Geophys. Res. Letters 18:2241-2244. Vermote E., D. Tanre and J.J. Morcrette. 1997. Second simulation of the satellite signal in the solar spectrum 6S: an overview. IEEE Trans. Geosci. Remote Sens. vol. 35 no. 3, pp. 675. Walter-Shea, E.A., J.M. Norman, and B.L. Blad. 1989. Leaf bidirectional reflectance and transmittance in corn and soybean. Remote Sensing of Environment. 29:161-174. Walter-Shea, E.A. and L.L. Biehl. 1990. Measuring vegetation spectral properties. Remote Sensing Review. 5:179-205. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List Of Acronyms 6S - Second Simulation of the Satellite Signal in the solar Spectrum ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System BRDF - Bidirectional Reflectance Distribution Function DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FFC-T - Focused Field Campaign-Thaw FFC-W - Focused Field Campaign-Winter FOV - Field of view IFC - Intensive Field Campaign IFOV - Instantaneous Field of View GMT - Greenwich Mean Time MMR - Modular Multiband Radiometer GSFC - Goddard Space Flight Center NASA - National Aeronautics and Space Administration NDVI - Normalized Difference Vegetation Index 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 PAR - Photosynthetically Active Radiation PARABOLA - Portable Apparatus for Rapid Acquisitions of BiDirectional Observations of Land and Atmosphere QA - Quality Assurance RSS - Remote Sensing Science SSA - Southern Study Area TM - Thematic Mapper SZA - Solar Zenith Angle URL - Uniform Resource Locator UTM - Universal Transverse Mercator 20. Document Information 20.1 Document Revision Date(s) Written: 18-Nov-1994 Last Updated: 07-Dec-1998 20.2 Document Review Date(s) BORIS Review: 28-Nov-1998 Science Review: 29-Jun-1998 20.3 Document ID None. 20.4 Citation The surface reflectance and transmitted radiance measured by PARABOLA were collected and analyzed by Dr. Donald W. Deering, Thomas F. Eck, Dr. Suraiya P. Ahmad, and Babu Banerjee as part of the Remote Sensing Science (RSS-01) study of the BOREAS experiment. 20.5 Document Curator 20.6 Document URL Keywords: Reflectance Transmittance Radiance PARABOLA Bidirectional Reflectance Boreal Forest RSS01_PARABOLA.doc 01/13/99