The Jet Propulsion Laboratory's (JPL's) Portable Apparatus for Rapid Acquisition of Bidirectional Observation of the Land and Atmosphere (PARABOLA), version III, instrument collected radiance data covering both the upwelling and downwelling hemispheres at the Sua Pan salt playa in the Magkadigkadi region of Botswana and at the Skukuza tower site in the Kruger National Park, South Africa between August 25 and October 2, 2000, during in the SAFARI 2000 Dry Season Aircraft Campaign. PARABOLA III is a sphere-scanning radiometer that provides multi-angle measurements of sky and ground radiances on a spherical grid of 5° in the zenith-to-nadir and azimuthal planes in eight spectral channels (444, 551, 581, 650, 860, 944, 1028, and 1650 nm). The experiment was designed to collect data necessary for multi-angle top-of-atmosphere radiance predictions for a vicarious calibration of the Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard the Terra satellite. Four of the PARABOLA channels (444, 551, 650, and 860 nm) are similar to those of the MISR sensor. Measurements were made on cloud-free days of Terra satellite overpasses.
Each data file contains radiance counts (ASCII integer values) for 8 bands for each 3-minute data collection. Zenith and azimuth angles are implied by radiance count positions in file. Additional files contain average dark current readings, empirically determined by covering the detectors. The data can be processed to radiance using a series of second order polynomial fit coefficients, provided in the documentation file, and dark current offset. Site-specific auxiliary information is also provided, for each date of PARABOLA data collection.
Coincident aircraft overflights occurred on September 16, 23, and 25 and collected aerial photographs, in-situ aerosol, and BRDF data on selected dates. See Myers (2004), Hobbs (2004), and Piketh et al., (2004a and 2004b) for more information.
Cite this data set as follows:
Helmlinger, M., W. Buermann, and F. Eckardt. 2005. SAFARI 2000 BRDF Measurements at Sua Pan and Skukuza, Dry Season 2000. Data set. Available on-line [http://daac.ornl.gov/] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/779.
Abdou, W. A., M. C. Helmlinger, J. E. Conel, S. Pilorz, C. J. Bruegge, B. J. Gaitley, and J. V. Martonchik. 2001. Ground measurements of surface bidirectional reflectance factor (BRF) and hemispherical directional reflectance factor (HDRF) of the land and atmosphere (PARABOLA III). J. Geophys. Res., Vol. 106: 11,967-11,976.
Bruegge, C. J., M. C. Helmlinger, J. E. Conel, B. J. Gaitley, and W. A. Abdou. 2000. PARABOLA III: a sphere-scanning radiometer for field determination of surface anisotropic reflectance functions. Remote Sensing Reviews, Vol 19: 75-94.
Hobbs, P. V. 2004. SAFARI 2000 CV-580 Aerosol and Cloud Data, Dry Season 2000 (CARG). Data set. Available on-line [www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
Myers, J. S. 2004. SAFARI 2000 ER-2 Color-IR Aerial Photography, Dry Season 2000. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
Piketh, S. J., T. Elias, and D. C. Stein. 2004a. SAFARI 2000 JRA Aerocommander Trace Gas, Aerosol, and CCN Data, Dry Season 2000. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
Piketh, S. J., T. Elias, and D. C. Stein. 2004b. SAFARI 2000 JRB Aerocommander Trace Gas and Aerosol Data, Dry Season 2000. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
PARABOLA Data Files
The file names include scan number, date, and time of data collection. For example, PARABOLA scan number 1 table on August 25, 2000 at 04:21 local time is named:
Each file contains 37 rows by 72 columns of ASCII integer values of radiance counts, separated by commas, for 8 bands for each 3 minute data collection. All of the data for the first band are reported, followed by a blank record, then the next band, and so on. Note that there is a 180° azimuthal offset between two groups of four bands each, depending on the head number. See spectral resolution section below.
|Radiance Counts||Proportional to physical radiance via quadratic fit coefficients with dark current offset.||Digital Numbers (DN or counts)||0-1048576|
|Zenith Angle |
(implied by DN position in file)
|Vertical position in array, reported in 5° increments. |
Row 1 = 0°, Row 37 = 180°.
(row position 1-37)
|Azimuth Angle |
(implied by DN position in file)
|Horizontal position in array, reported in 5° increments. |
Column 1 = 0°, Column 72 = 355°
Absolute alignment to geographic north determined by apparent sun position and ephemeris.
(column position 1-72)
PARABOLA Average Dark Current Readings
Each file contains a set of average dark current readings, in ASCII .csv format, empirically determined by covering the detectors. Zenith and azimuth are not actual reported values in the data files, rather, the 5 degree field-of-view increments are implied by the DN position within the data array.
PARABOLA Site-Specific Auxiliary Information
The parameters listed below are stored in the ASCII text (.csv) file, parabola_aux_info.csv. One record for each date of PARABOLA data collection. The temperatures and pressures were collected around the time of the Terra overpass (10:00-11:00 am local time).
|Date||Day, Month, Year of measurement||DDMMYYYY||Magellan GPS||Aug & Sep 2000|
|Time||Time of measurement (Terra overpass)||hhmm (UTC)||Magellan GPS||0820-0845|
|Latitude||Instrument location, latitude||decimal degrees||Magellan GPS||Southern Africa|
|Longitude||Instrument location, longitude||decimal degrees||Magellan GPS||Southern Africa|
|Pressure||barometric pressure||millibars||Davis Met Package||916-990 mb|
|Temperature||air temperature measured by electronic thermometer||°C||Davis Met Package||21-32° C|
|Az_Offset||azimuthal offset estimated by comparison of apparent solar position to ephemeral prediction.||degrees||Calculated. User must verify this quantity on a case-by-case basis.||0-180°|
Additional information about the site locations, data collection, PARABOLA instrumentation, spectral and temporal resolution, radiance conversion, and quality assessment is found in the following file: http://daac.ornl.gov/daacdata/safari2k/field_campaign/sua_pan_skukuza_brdf/comp/ sua_pan_skukuza_brdf_readme.pdf.