Stefanie Herrmann - What's in a pixel? Using remote sensing to study rainfall variability and land cover changes in the Sahel.
Vegetation cover in the semi-arid Sahel region of West Africa is characterized by high annual and interannual variability, which can be attributed to rainfall patterns and human activities such as extraction of woody vegetation, cultivation and grazing. The year-to-year timing, intensity, and duration of the growing season have important implications for the economies of the region, which are dominated by the agricultural sector.
Stefanie has been working with remote sensing data, mostly from the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors, to study the trends in and relationships between rainfall and vegetation greenness at regional scales. One of her sites of interest is the Central Plateau of Burkina Faso, where remotely-sensed vegetation index data have shown a greening trend since the mid-1990s, which has been paralleled by an increase in rainfall. Whereas there is some ground evidence of farmer driven rehabilitation of formerly degraded land in parts of the area, what the “greening” means on the ground in other parts has not yet been established. Since the Normalized Difference Vegetation Index (NDVI) is an aggregate measure of photosynthetic activity, it does not carry any information on the contributions of different types of photosynthetic vegetation – such as trees, shrubs and grasses – to the overall greenness. Including the temporal dimension, that is vegetation phenology or seasonality, can provide additional information.
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ASP Spotlight February 2008
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