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/m) 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. Halthore. 1997. Atmospheric 
aerosol and water vapor characteristics over north central Canada during 
BOREAS, Journal of Geophysical Research (JGR), BOREAS Special Issue, 102(D24), 
Dec. 1997, pp. 29737-29745.

Middleton, E.M., D.W. Deering and S.P. Ahmad. 1987. Surface Anisotropy and 
Hemispheric Reflectance of Semi-Arid Plant Communities. Remote Sens. Environ. 
23:193-212.

Otterman, J., D.W. Deering, and T.F. Eck. 1987. Techniques of Ground-Truth 
Measurements of Desert-Scrub Structure. Advances in Space Res. 7:153-158.

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 
(JGR), BOREAS Special Issue, 102(D24), Dec. 1997, pp. 28731-28770.  

Shephard, M.K., R.E. Arvidson, E.A. Guinness, and D.W. Deering. 1991. 
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