Spectra of Mixed Pixels: Do They Represent the Actual Land Cover on the Ground? - a Case Study for a Wet Savanna Ecosystem in Uganda

Due to increased availability and affordable cost of TM7 data, one envisages its widespread use for land cover mapping in many developing countries. There is need to establish not only the potential but also the limitations of TM data for land cover mapping in some natural ecosystems of the tropics. Uganda is a tropical country with well-distributed rainfall and its landscapes are characterised by luxuriant vegetation, remaining healthy throughout the year. Wet savanna ecosystems, common in Uganda, are characterised by wood-grass mixtures of variable wood density. Mixed pixels characteristic of TM data are believed to effect land cover mapping in wet savanna ecosystems. Given the high expenses required to generate land cover maps from airborne data, TM and SPOT data are preferred for land cover mapping in the country, irrespective of the nature of the landscapes. For example, a number of vegetation mapping exercises have been completed for two savanna national parks using TM and SPOT data. What is not yet understood, by the wider conservation community in Uganda, is whether TM or SPOT data is suitable for land cover mapping of wet savanna ecosystems, despite its availability and affordability. In this study, high-resolution digital airborne data was used as a validation tool to investigate the effect of mixed pixel spectra on land cover mapping in a wet savanna ecosystem. Results indicate that mixed pixels adversely affect land cover mapping in savanna compared to homogeneous landscapes. * Corresponding author.