Data from the Tracing Radiation and Architecture of Canopies (TRAC) instrument were collected at five sites along the International Geosphere-Biosphere Programme (IGBP) Kalahari Transect, including Mongu in Zambia and Pandamatenga, Maun, Okwa River Crossing, and Tshane in Botswana, during the 2000 wet season field campaign (March-April) of SAFARI 2000. At the Mongu site, TRAC measurements began in August of 1999 and continued beyond the 2000 wet season field campaign, about every month for the rest of 2000.
The TRAC instrument contains pyranometers that are sensitive to photosynthetically active radiation (PAR) at 400-700 nm. The TRAC measures the PAR flux transmitted through the overstory canopy continuously at 32 Hz. The parameters derived from the TRAC instrument include estimates of plant or leaf area index (PAI, LAI), overstory gap fraction, and clumping index.
At each site the TRAC instrument was carried along three parallel transects, each 750 m long and spaced 250 m apart. Measurements were made every 25 m along the transects. The length and spacing of the transects were chosen to sample an area large enough to be representative of a 1-km MODIS pixel.
The data files are stored as ASCII text files, one file per transect, site, and date, with column headers. There are also summary files (ASCII text) containing mean values of each derived parameter over an entire transect for each collection date.
Cite this data set as follows:
Privette, J. L., and M. Mukelabai. 2005. SAFARI 2000 Leaf Area Index and Canopy Structure, Kalahari Transect, 1999-2000. 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/771.
Privette, J. L., R. B. Myneni, Y. Knyazikhin, M. Mukelabai, Y. Tian, Y. Wang, G. Roberts, and S. Leblanc. 2002. Early spatial and temporal validation of MODIS LAI in the Southern Africa Kalahari. Remote Sens. Environ., 83: 232-243.
Privette, J. L., Y. Tian, G. Roberts, R. J. Scholes, Y. Wang, K. Caylor, and M. Mukelabai. 2004. Structural characterization and relationships in Kalahari woodlands and savannas. Global Ch. Biol., 10(3): 281-291.
The data files are stored as ASCII text files, one file per transect, site, and date, with column headers. The file naming convention is site_dd_mm_y.txt, where site is a single-character indicator for site, dd and mm are the day and month of data collection, and y is the last digit of the year of data collection. The mean solar zenith angle at the time of the measurements is included at the end of the LAI data records for each file.
Kalahari Transect Sites
Mongu (Kataba Forest)
-15° 26' 16"
23° 15' 10"
-18° 39' 19"
25° 30' 01"
-19° 55' 22"
23° 35' 40"
Ghanzi/Okwa River Crossing
-22° 24' 33"
21° 42' 47"
-24° 09' 51"
21° 53' 34"
Column Name Definition Units/Format Segment Number Identification of the sequential 25 m segment along the 750 m transect (usually starting from west end) unitless LAI leaf area index, assuming stem_area=0 and accounts for clumping m2/m2 PAIe effective plant area index, does not account for clumping m2/m2 Omega Clumping Index fraction GapFrSZA Gap Fraction at the solar_zenith_angle fraction GapFrVert Gap Fraction overhead (i.e., at zenith) fraction
Segment LAI PAIe Omega GapFrSZA GapFrVert 1 0.280 0.277 0.989 0.573 0.871 2 0.291 0.283 0.972 0.565 0.868 3 0.437 0.421 0.964 0.428 0.810 4 0.329 0.329 1.000 0.515 0.848 5 0.413 0.358 0.867 0.486 0.836
There are also two summary files (ASCII text) containing mean values of each derived parameter over an entire transect for each collection date. One file contains mean values for the Mongu site; the other for the four sites in Botswana.
Additional information about the theory of measurement, data collection and processing, data format, and study area is found in the companion file: http://daac.ornl.gov/daacdata/safari2k/field_campaign/kt_lai_trac/comp/kt_lai_trac_readme.pdf.