Classification of ponds from high-spatial resolution remote sensing
Extract of Remote Sensing of Environment 106 (2007) 66-74.
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During the rainy season the abundance of mosquitoes over the Ferlo region (Senegal) is linked to dynamic, vegetation cover and turbidity of
temporary and relatively small ponds. The latter create a variable environment where mosquitoes can thrive and thus contribute to diffusion and
transmission of diseases such as the Rift Valley Fever (RVF, with Aedes vexans arabiensis and Culex poicilipes mosquitoes) in the Ferlo. The
small size and complex distribution of ponds require the use of high-spatial resolution satellite images for adequate detection. Here the use of
SPOT-5 images (10 m-resolution) allows for detailed assessment of spatio-temporal evolution of ponds, through two new indices : i.e., the
Normalized Difference Pond Index (NDPI), and the Normalized Difference Turbidity Index (NDTI). Small ponds less than 0.5 ha dominate
whatever the time period. For example they represent nearly 65% of the total ponds during the peak of the rainy season, up to 90% at the end of
the same season. Moreover, another product is proposed : the Zone Potentially Occupied by Mosquitoes (ZPOM). During the apex of the summer
monsoon, it is found that RVF mosquitoes occupy 25% of the Ferlo region, while only 0.9% of the same area is covered by ponds. Overlapping
areas occupied by grazing cattle and mosquitoes, enhance RVF virus transmission. The remotely sensed operational indices and products
presented here are meant to better understand the mechanisms at stake and to contribute to the development of early warning systems in a
changing climate and environment.
© 2006 Elsevier Inc. All rights reserved.
Keywords : Remote sensing, Rift Valley Fever ; Ponds ; Aedes ; Culex ; Senegal
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 Centre de Suivi Ecologique (CSE), Laboratoire de Physique de l’Atmosphère et de l’Océan Siméon Fongang (LPAO-SF), Dakar, Sénégal
 Centre National d’Etudes Spatiales (CNES), Toulouse, France