This data set was collected during the February-March 2000 wet season and September 2000 dry season field campaigns of SAFARI 2000. Mongu in Zambia and Pandematenga (aka Kasane) and Tshane in Botswana were visited during the wet season campaign. Dry season data are for Mongu only.
Hemispherical photographs, from which Plant Area Index (PAI) estimates are derived, were obtained at the field sites to characterize vegetation structural changes along the Kalahari Transect. At each site photographs were collected using a Nikon Coolpix 950 digital camera with a fish-eye lens mounted on a tripod every 25 m along three transects, each 750 m in length.
The methodology of van Gardingen et al. (1999) was applied to process the data. The photographs are classified into sky and vegetation (trunk, green and senescent leaves, and branches) using an unsupervised classification scheme. Derivation of gap fraction estimates was carried out by dividing the azimuth sector for each view zenith into 72 equal area segments with the gap fraction estimated for each segment. The average azimuth segmented gap fraction was used to characterize the gap fraction at the current view zenith angle. This approach attempts to reduce the underestimation introduced by assuming a random distribution in clumped canopies. PAI estimates were derived from the gap fraction data using Miller's (1967) formula for average foliage density.
Data are in comma-delimited ASCII files, one for each transect at each site, containing a 5-line header, then a blank line, column names, and the two-column data (sample number and PAI).
Cite this data set as follows:
Roberts, G. 2005. SAFARI 2000 PAI Estimates from Hemispherical Photography, Kalahari Transect. 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/774.
van Gardingen, P. R., G. E. Jackson, S. Hernandez-Daumas, G. Russell, and L. Sharp. 1999. Leaf area index estimates obtained for clumped canopies using hemispherical photography. Agricultural and Forest Meteorology, 94(3-4): 243-257.
Miller, J. B. 1967. A formula for average foliage density. Aust. J. Bot. 15: 141-144.
The PAI estimates are provided in comma-delimited ASCII files, one for each transect at each site. At each site three 750-m transects were established (termed A, B, and N -- spaced 250 m apart). Measurements were made every 25 m (31 measurements per transect). The sample numbers within the data files are numbered in the order that they were collected, starting from either the East or West end of the transect, the lowest number representing the first point measurement on the transect. (See the tables in companion file for more information.) The file names are as follows:
pai_site_transect_2000-season.csv
where site is either Kasane, Mongu, or Tshane; transect is either tranA (transect A), tranB (transect B), or tranN (transect N); and season is either Wet or Dry.
Within each file, there is a 5-line header, then a blank line, then column names, then the two-column data (sample number and PAI).
PAI Data File Structure
Column Description Header Title SAFARI 2000 PAI Estimates from Hemispherical Photography PI Name Gareth Roberts (groberts@geog.ucl.ac.uk) Site Kasane, Botswana, Mongu, Zambia, or Tshane, Botswana Season Dry Season 2000or Wet Season 2000 Transect A, B, or N; and Direction (east to west) or (west to east) Data Sample The sample number (1 to 31) which designates how many 25 m steps along the transect the data was taken, from the starting point (west or east) PAI Plant Area Index, derived from a hemispherical photograph taken at the location
Global Positioning System (GPS) coordinates for the grid transect end points were collected at the Kalahari Transect sites and can be found in the file GPS_coords_transec_endpts.txt.
The following is a sample file listing for the file pai_kasane_tranA_2000-wet.csv.
Additional information about the data collection methodology and data format is found in the companion file: http://daac.ornl.gov/daacdata/safari2k/field_campaign/kt_pai_estimates/comp/kt_pai_estimates_readme.pdf.
2004/12/2
2004/12/2
webmaster@www.daac.ornl.gov