Géoinformatique et géostatistique : un aperçu

Multitemporal Analysis of the City of Nouakchott (Mauritania) Based on ENVISAT ASAR Images

Hachemi K, Thomas YF, Senhoury AOE-M and Martin T

Multitemporal Analysis of the City of Nouakchott (Mauritania) Based on ENVISAT ASAR Images

The city of Nouakchott lies between the Atlantic Ocean to its west and the desert to its east. It is built on an almost level site located partially below sea level and is protected by a relatively narrow line of poorly vegetated coastal dunes displaying an average width of 150 m and an altitude less than 6 m. This setting fosters seawater incursion caused by storm surges. The city is also fractionated by a succession of highly mobile dunes which follow the northwestsouthwest wind lines with altitudes of up to twenty meters. The construction in 1986 of the “Port de l’Amitié” given its depth of 10 m, induced: (i) significant coastline growth north of the harbor; (ii) significant erosion south of the harbor. This rapid coastline evolution produced weakening of coastal dunes in certain sectors and led on several occasions, namely, December 1997, to seawater incursion. Rapid expansion, increased density of the urban fabric, erosion of costal dunes, increased frequency and intensity of rainfall, rising sea level, rising groundwater levels as well as densification of transportation and industrial infrastructures have made this city of over one million inhabitants increasingly vulnerable. Our job was to document urban sprawl and quantify coastline evolution via a diachronic study employing ENVISAT satellite ASAR radar imaging. For this, we produced 9 amplitude images at different dates (2004, 2005, 2008, 2009 and 2010) calibrated and Georeferenced to 20 meter resolution (WGS 84, UTM cartographic projection).