Mapping ecological conditions in the Okavango delta, Botswana using fine and coarse resolution systems including simulated SPOT vegetation imagery

Aspects of wetland monitoring in southern Africa are significant in the light of the Ramsar Convention, which has recently been signed by Botswana. The present work initially indicated that most ecological units in the Okavango delta can be identified and mapped using fine resolution satellite imagery and aerial photography. A second step involved assessing which of these units could also be identified using coarse resolution imagery. Contrasting results were obtained from a relatively high quality solid state sensor system (simulated SPOT 4-VEGETATION) and a relatively low quality system (NOAA-AVHRR). The extent of the water surface in the flooded areas could not be accurately mapped using NOAA-AVHRR data because of pixel saturation effects. However the presence of water was generally located using AVHRR data. The ecologically significant riparian woodlands were found to saturate pixel response on Thematic Mapper (TM) imagery. As a result of detailed comparisons, it was found that simulated SPOT VEGETATION data could be used for mapping and monitoring major changes in grassed floodplains and wooded peripheral drylands which are not spectrally separable using NOAA-AVHRR data. Most ecological change in the Okavango delta which involves such small-scale transformations as thicket development (shrub growth) and minor land-use changes related to tourism, requires the use of finer resolution systems for instance high resolution false colour aerial photography in conjunction with fieldwork. In terms of overall needs for mapping and monitoring wetland conditions in semi-arid areas it appears that major changes in flood extent and related floodplain drying vegetation changes are best detected accurately using fine resolution (TM) satellite data. Large-scale ecological changes can be semi-quantified using high quality imagery data at coarse resolutions similar to SPOT VEGETATION data.