A LANDSAT ANALYSIS OF RANGE CONDITIONS IN THE BOTSWANA KALAHARI DROUGHT

An analysis was undertaken of range conditions in the Botswana Kalahari during the 1980-1987 drought. Information from Landsat MSS print and tape data was field-checked both aerially and on the ground through two wet seasons. Comparison of 327 field and digitized aerial photograph sites with spectral data on MSS4, 5 and 7 in relation to hues on Landsat colour composite print data revealed three main spectral-vegetation types. Type 1 darkened areas comprise green tree and shrub vegetation, shown as varying tones of blue-green hues. The rate of darkening varied with the soil substrate but regression analysis showed that higher green vegetation densities occurred at lower MSS4 and 5 reflectance values. Type 2 areas combine darkened areas with areas of high near-infrared reflectance. Vegetation indices do not predict green leaf cover in type 1 or type 2 areas. This is best achieved through density slicing on MSS5. Type 3 areas show high near-infrared and low red reflectance. Green leaf cover can be predicted both by density slicing on MSS5 and through vegetation-index analysis. Since 70 per cent of the Kalahari exhibited darkening, an attempt was made to resolve darkening components using a hand-held radiometer. Results indicated that the within-plant shadow components on thinly leaved trees and shrubs gave rise to darkening. An assessment made of the remaining plant material (browse) showed that large areas of the Kalahari were suffering from poor to intermediate range conditions during the mid to late drought period.