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This work describes the setting up of a preprocessed archive of AVHRR GAC (4km) data on West Africa covering the period 1981-1989. Comparison of these data with AVHRR HRPT (1km) data suggests that both resolutions are equally capable of registering change encompassing the major regions in their entirety. It is shown that the sampling of GAC data greatly reduces the capacity of the data to detect localised phenomena such as fires. It is then shown how AVHRR HRPT data can be used to obtain a spatio-temporal picture of the changing state of the surface in the five drainage basins of West Africa. Weekly vegetation indices derived from AVHRR data during 1984 are compared to official statistics for millet and sorghum for 83 administrative areas of Senegal, Mali, Burkina Faso and Niger. The vegetation indices provide sufficient evidence to account for 2/3 of the variability in yield from the beginning of September - that is, one or two months before the harvest, depending on the region. Integrated indices do not prove to be superior to instantaneous indices. With integrated indices, the change with time of the parameters of regression is gradual and can be modelled. A deterministic model applied to the same data from AVHRR gives rise to results compatible with the agricultural statistics. It highlights the inherent limitations of observations at very low resolution and the necessity of extracting information which is directly related to agriculture. This is confirmed when seasonal behaviour of the agricultural and non-agricultural sectors is compared using AVHRR LAC and HRPT data.

Additional information

Authors: BARTHOLOMÉ E, JRC Ispra (IT)
Bibliographic Reference: EUR 12847 FR (1990) 64 pp., MF, ECU 4, blow-up copy ECU 8.75
Availability: (2)
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